clean up some comments

[proxmark3-svn] / common / lfdemod.c

//-----------------------------------------------------------------------------
// Copyright (C) 2014
//
// This code is licensed to you under the terms of the GNU GPL, version 2 or,
// at your option, any later version. See the LICENSE.txt file for the text of
// the license.
//-----------------------------------------------------------------------------
// Low frequency demod/decode commands
//-----------------------------------------------------------------------------

#include <stdlib.h>
#include <string.h>
#include "lfdemod.h"

//by marshmellow
//get high and low with passed in fuzz factor. also return noise test = 1 for passed or 0 for only noise
int getHiLo(uint8_t *BitStream, size_t size, int *high, int *low, uint8_t fuzzHi, uint8_t fuzzLo)
{
        *high=0;
        *low=255;
        // get high and low thresholds 
        for (int i=0; i < size; i++){
                if (BitStream[i] > *high) *high = BitStream[i];
                if (BitStream[i] < *low) *low = BitStream[i];
        }
        if (*high < 123) return -1; // just noise
        *high = (int)(((*high-128)*(((float)fuzzHi)/100))+128);
        *low = (int)(((*low-128)*(((float)fuzzLo)/100))+128);
        return 1;
}

//by marshmellow
//takes 1s and 0s and searches for EM410x format - output EM ID
uint64_t Em410xDecode(uint8_t *BitStream, size_t *size, size_t *startIdx)
{
        //no arguments needed - built this way in case we want this to be a direct call from "data " cmds in the future
        //  otherwise could be a void with no arguments
        //set defaults
        uint64_t lo=0;
        uint32_t i = 0;
        if (BitStream[10]>1){  //allow only 1s and 0s
                // PrintAndLog("no data found");
                return 0;
        }
        uint8_t parityTest=0;
        // 111111111 bit pattern represent start of frame
        uint8_t frame_marker_mask[] = {1,1,1,1,1,1,1,1,1};
        uint32_t idx = 0;
        uint32_t ii=0;
        uint8_t resetCnt = 0;
        while( (idx + 64) < *size) {
 restart:
                // search for a start of frame marker
                if ( memcmp(BitStream+idx, frame_marker_mask, sizeof(frame_marker_mask)) == 0)
                { // frame marker found
                        *startIdx=idx;
                        idx+=9;
                        for (i=0; i<10;i++){
                                for(ii=0; ii<5; ++ii){
                                        parityTest ^= BitStream[(i*5)+ii+idx];
                                }
                                if (!parityTest){ //even parity
                                        parityTest=0;
                                        for (ii=0; ii<4;++ii){
                                                lo=(lo<<1LL)|(BitStream[(i*5)+ii+idx]);
                                        }
                                        //PrintAndLog("DEBUG: EM parity passed parity val: %d, i:%d, ii:%d,idx:%d, Buffer: %d%d%d%d%d,lo: %d",parityTest,i,ii,idx,BitStream[idx+ii+(i*5)-5],BitStream[idx+ii+(i*5)-4],BitStream[idx+ii+(i*5)-3],BitStream[idx+ii+(i*5)-2],BitStream[idx+ii+(i*5)-1],lo);
                                }else {//parity failed
                                        //PrintAndLog("DEBUG: EM parity failed parity val: %d, i:%d, ii:%d,idx:%d, Buffer: %d%d%d%d%d",parityTest,i,ii,idx,BitStream[idx+ii+(i*5)-5],BitStream[idx+ii+(i*5)-4],BitStream[idx+ii+(i*5)-3],BitStream[idx+ii+(i*5)-2],BitStream[idx+ii+(i*5)-1]);
                                        parityTest=0;
                                        idx-=8;
                                        if (resetCnt>5)return 0; //try 5 times
                                        resetCnt++;
                                        goto restart;//continue;
                                }
                        }
                        //skip last 5 bit parity test for simplicity.
                        *size = 64;
                        return lo;
                }else{
                        idx++;
                }
        }
        return 0;
}

//by marshmellow
//takes 2 arguments - clock and invert both as integers
//attempts to demodulate ask while decoding manchester
//prints binary found and saves in graphbuffer for further commands
int askmandemod(uint8_t *BinStream, size_t *size, int *clk, int *invert)
{
        int i;
        int clk2=*clk;
        *clk=DetectASKClock(BinStream, *size, *clk); //clock default

        // if autodetected too low then adjust  //MAY NEED ADJUSTMENT
        if (clk2==0 && *clk<8) *clk =64;
        if (clk2==0 && *clk<32) *clk=32;
        if (*invert != 0 && *invert != 1) *invert=0;
        uint32_t initLoopMax = 200;
        if (initLoopMax > *size) initLoopMax=*size;
        // Detect high and lows
        // 25% fuzz in case highs and lows aren't clipped [marshmellow]
        int high, low, ans;
        ans = getHiLo(BinStream, initLoopMax, &high, &low, 75, 75);
        if (ans<1) return -2; //just noise

        // PrintAndLog("DEBUG - valid high: %d - valid low: %d",high,low);
        int lastBit = 0;  //set first clock check
        uint32_t bitnum = 0;     //output counter
        int tol = 0;  //clock tolerance adjust - waves will be accepted as within the clock if they fall + or - this value + clock from last valid wave
        if (*clk<=32)tol=1;    //clock tolerance may not be needed anymore currently set to + or - 1 but could be increased for poor waves or removed entirely
        int iii = 0;
        uint32_t gLen = *size;
        if (gLen > 3000) gLen=3000;
        uint8_t errCnt =0;
        uint32_t bestStart = *size;
        uint32_t bestErrCnt = (*size/1000);
        uint32_t maxErr = (*size/1000);
        // PrintAndLog("DEBUG - lastbit - %d",lastBit);
        // loop to find first wave that works
        for (iii=0; iii < gLen; ++iii){
                if ((BinStream[iii] >= high) || (BinStream[iii] <= low)){
                        lastBit=iii-*clk;
                        errCnt=0;
                        // loop through to see if this start location works
                        for (i = iii; i < *size; ++i) {
                                if ((BinStream[i] >= high) && ((i-lastBit) > (*clk-tol))){
                                        lastBit+=*clk;
                                } else if ((BinStream[i] <= low) && ((i-lastBit) > (*clk-tol))){
                                        //low found and we are expecting a bar
                                        lastBit+=*clk;
                                } else {
                                        //mid value found or no bar supposed to be here
                                        if ((i-lastBit)>(*clk+tol)){
                                                //should have hit a high or low based on clock!!

                                                //debug
                                                //PrintAndLog("DEBUG - no wave in expected area - location: %d, expected: %d-%d, lastBit: %d - resetting search",i,(lastBit+(clk-((int)(tol)))),(lastBit+(clk+((int)(tol)))),lastBit);

                                                errCnt++;
                                                lastBit+=*clk;//skip over until hit too many errors
                                                if (errCnt>(maxErr)) break;  //allow 1 error for every 1000 samples else start over
                                        }
                                }
                                if ((i-iii) >(400 * *clk)) break; //got plenty of bits
                        }
                        //we got more than 64 good bits and not all errors
                        if ((((i-iii)/ *clk) > (64+errCnt)) && (errCnt<maxErr)) {
                                //possible good read
                                if (errCnt==0){
                                        bestStart=iii;
                                        bestErrCnt=errCnt;
                                        break;  //great read - finish
                                }
                                if (errCnt<bestErrCnt){  //set this as new best run
                                        bestErrCnt=errCnt;
                                        bestStart = iii;
                                }
                        }
                }
        }
        if (bestErrCnt<maxErr){
                //best run is good enough set to best run and set overwrite BinStream
                iii=bestStart;
                lastBit = bestStart - *clk;
                bitnum=0;
                for (i = iii; i < *size; ++i) {
                        if ((BinStream[i] >= high) && ((i-lastBit) > (*clk-tol))){
                                lastBit += *clk;
                                BinStream[bitnum] = *invert;
                                bitnum++;
                        } else if ((BinStream[i] <= low) && ((i-lastBit) > (*clk-tol))){
                                //low found and we are expecting a bar
                                lastBit+=*clk;
                                BinStream[bitnum] = 1-*invert;
                                bitnum++;
                        } else {
                                //mid value found or no bar supposed to be here
                                if ((i-lastBit)>(*clk+tol)){
                                        //should have hit a high or low based on clock!!

                                        //debug
                                        //PrintAndLog("DEBUG - no wave in expected area - location: %d, expected: %d-%d, lastBit: %d - resetting search",i,(lastBit+(clk-((int)(tol)))),(lastBit+(clk+((int)(tol)))),lastBit);
                                        if (bitnum > 0){
                                                BinStream[bitnum]=77;
                                                bitnum++;
                                        }

                                        lastBit+=*clk;//skip over error
                                }
                        }
                        if (bitnum >=400) break;
                }
                *size=bitnum;
        } else{
                *invert=bestStart;
                *clk=iii;
                return -1;
        }
        return bestErrCnt;
}

//by marshmellow
//encode binary data into binary manchester 
int ManchesterEncode(uint8_t *BitStream, size_t size)
{
        size_t modIdx=20000, i=0;
        if (size>modIdx) return -1;
  for (size_t idx=0; idx < size; idx++){
        BitStream[idx+modIdx++] = BitStream[idx];
        BitStream[idx+modIdx++] = BitStream[idx]^1;
  }
  for (; i<(size*2); i++){
        BitStream[i] = BitStream[i+20000];
  }
  return i;
}

//by marshmellow
//take 10 and 01 and manchester decode
//run through 2 times and take least errCnt
int manrawdecode(uint8_t * BitStream, size_t *size)
{
        int bitnum=0;
        int errCnt =0;
        int i=1;
        int bestErr = 1000;
        int bestRun = 0;
        int ii=1;
        for (ii=1;ii<3;++ii){
                i=1;
                for (i=i+ii;i<*size-2;i+=2){
                        if(BitStream[i]==1 && (BitStream[i+1]==0)){
                        } else if((BitStream[i]==0)&& BitStream[i+1]==1){
                        } else {
                                errCnt++;
                        }
                        if(bitnum>300) break;
                }
                if (bestErr>errCnt){
                        bestErr=errCnt;
                        bestRun=ii;
                }
                errCnt=0;
        }
        errCnt=bestErr;
        if (errCnt<20){
                ii=bestRun;
                i=1;
                for (i=i+ii;i < *size-2;i+=2){
                        if(BitStream[i] == 1 && (BitStream[i+1] == 0)){
                                BitStream[bitnum++]=0;
                        } else if((BitStream[i] == 0) && BitStream[i+1] == 1){
                                BitStream[bitnum++]=1;
                        } else {
                                BitStream[bitnum++]=77;
                                //errCnt++;
                        }
                        if(bitnum>300) break;
                }
                *size=bitnum;
        }
        return errCnt;
}

//by marshmellow
//take 01 or 10 = 0 and 11 or 00 = 1
int BiphaseRawDecode(uint8_t *BitStream, size_t *size, int offset, int invert)
{
        uint8_t bitnum=0;
        uint32_t errCnt =0;
        uint32_t i;
        i=offset;
        for (;i<*size-2; i+=2){
                if((BitStream[i]==1 && BitStream[i+1]==0) || (BitStream[i]==0 && BitStream[i+1]==1)){
                        BitStream[bitnum++]=1^invert;
                } else if((BitStream[i]==0 && BitStream[i+1]==0) || (BitStream[i]==1 && BitStream[i+1]==1)){
                        BitStream[bitnum++]=invert;
                } else {
                        BitStream[bitnum++]=77;
                        errCnt++;
                }
                if(bitnum>250) break;
        }
        *size=bitnum;
        return errCnt;
}

//by marshmellow
//takes 2 arguments - clock and invert both as integers
//attempts to demodulate ask only
//prints binary found and saves in graphbuffer for further commands
int askrawdemod(uint8_t *BinStream, size_t *size, int *clk, int *invert)
{
        uint32_t i;
        // int invert=0;  //invert default
        int clk2 = *clk;
        *clk=DetectASKClock(BinStream, *size, *clk); //clock default
        //uint8_t BitStream[502] = {0};

        //HACK: if clock not detected correctly - default
        if (clk2==0 && *clk<8) *clk =64;
        if (clk2==0 && *clk<32 && clk2==0) *clk=32;
        if (*invert != 0 && *invert != 1) *invert =0;
        uint32_t initLoopMax = 200;
        if (initLoopMax > *size) initLoopMax=*size;
        // Detect high and lows
        //25% fuzz in case highs and lows aren't clipped [marshmellow]
        int high, low, ans;
        ans = getHiLo(BinStream, initLoopMax, &high, &low, 75, 75);
        if (ans<1) return -2; //just noise

        //PrintAndLog("DEBUG - valid high: %d - valid low: %d",high,low);
        int lastBit = 0;  //set first clock check
        uint32_t bitnum = 0;     //output counter
        uint8_t tol = 0;  //clock tolerance adjust - waves will be accepted as within the clock
                          //  if they fall + or - this value + clock from last valid wave
        if (*clk == 32) tol=1;    //clock tolerance may not be needed anymore currently set to
                                  //  + or - 1 but could be increased for poor waves or removed entirely
        uint32_t iii = 0;
        uint32_t gLen = *size;
        if (gLen > 500) gLen=500;
        uint8_t errCnt =0;
        uint32_t bestStart = *size;
        uint32_t bestErrCnt = (*size/1000);
        uint32_t maxErr = bestErrCnt;
        uint8_t midBit=0;
        //PrintAndLog("DEBUG - lastbit - %d",lastBit);
        //loop to find first wave that works
        for (iii=0; iii < gLen; ++iii){
                if ((BinStream[iii]>=high) || (BinStream[iii]<=low)){
                        lastBit=iii-*clk;
                        //loop through to see if this start location works
                        for (i = iii; i < *size; ++i) {
                                if ((BinStream[i] >= high) && ((i-lastBit)>(*clk-tol))){
                                        lastBit+=*clk;
                                        midBit=0;
                                } else if ((BinStream[i] <= low) && ((i-lastBit)>(*clk-tol))){
                                        //low found and we are expecting a bar
                                        lastBit+=*clk;
                                        midBit=0;
                                } else if ((BinStream[i]<=low) && (midBit==0) && ((i-lastBit)>((*clk/2)-tol))){
                                        //mid bar?
                                        midBit=1;
                                } else if ((BinStream[i]>=high) && (midBit==0) && ((i-lastBit)>((*clk/2)-tol))){
                                        //mid bar?
                                        midBit=1;
                                } else if ((i-lastBit)>((*clk/2)+tol) && (midBit==0)){
                                        //no mid bar found
                                        midBit=1;
                                } else {
                                        //mid value found or no bar supposed to be here

                                        if ((i-lastBit)>(*clk+tol)){
                                                //should have hit a high or low based on clock!!
                                                //debug
                                                //PrintAndLog("DEBUG - no wave in expected area - location: %d, expected: %d-%d, lastBit: %d - resetting search",i,(lastBit+(clk-((int)(tol)))),(lastBit+(clk+((int)(tol)))),lastBit);

                                                errCnt++;
                                                lastBit+=*clk;//skip over until hit too many errors
                                                if (errCnt > ((*size/1000))){  //allow 1 error for every 1000 samples else start over
                                                        errCnt=0;
                                                        break;
                                                }
                                        }
                                }
                                if ((i-iii)>(500 * *clk)) break; //got enough bits
                        }
                        //we got more than 64 good bits and not all errors
                        if ((((i-iii)/ *clk) > (64+errCnt)) && (errCnt<(*size/1000))) {
                                //possible good read
                                if (errCnt==0){
                                        bestStart=iii;
                                        bestErrCnt=errCnt;
                                        break;  //great read - finish
                                } 
                                if (errCnt<bestErrCnt){  //set this as new best run
                                        bestErrCnt=errCnt;
                                        bestStart = iii;
                                }
                        }
                }
        }
        if (bestErrCnt<maxErr){
                //best run is good enough - set to best run and overwrite BinStream
                iii=bestStart;
                lastBit = bestStart - *clk;
                bitnum=0;
                for (i = iii; i < *size; ++i) {
                        if ((BinStream[i] >= high) && ((i-lastBit) > (*clk-tol))){
                                lastBit += *clk;
                                BinStream[bitnum] = *invert;
                                bitnum++;
                                midBit=0;
                        } else if ((BinStream[i] <= low) && ((i-lastBit) > (*clk-tol))){
                                //low found and we are expecting a bar
                                lastBit+=*clk;
                                BinStream[bitnum] = 1-*invert;
                                bitnum++;
                                midBit=0;
                        } else if ((BinStream[i]<=low) && (midBit==0) && ((i-lastBit)>((*clk/2)-tol))){
                                //mid bar?
                                midBit=1;
                                BinStream[bitnum] = 1 - *invert;
                                bitnum++;
                        } else if ((BinStream[i]>=high) && (midBit==0) && ((i-lastBit)>((*clk/2)-tol))){
                                //mid bar?
                                midBit=1;
                                BinStream[bitnum] = *invert;
                                bitnum++;
                        } else if ((i-lastBit)>((*clk/2)+tol) && (midBit==0)){
                                //no mid bar found
                                midBit=1;
                                if (bitnum!=0) BinStream[bitnum] = BinStream[bitnum-1];
                                bitnum++;
                                
                        } else {
                                //mid value found or no bar supposed to be here
                                if ((i-lastBit)>(*clk+tol)){
                                        //should have hit a high or low based on clock!!

                                        //debug
                                        //PrintAndLog("DEBUG - no wave in expected area - location: %d, expected: %d-%d, lastBit: %d - resetting search",i,(lastBit+(clk-((int)(tol)))),(lastBit+(clk+((int)(tol)))),lastBit);
                                        if (bitnum > 0){
                                                BinStream[bitnum]=77;
                                                bitnum++;
                                        }

                                        lastBit+=*clk;//skip over error
                                }
                        }
                        if (bitnum >=400) break;
                }
                *size=bitnum;
        } else{
                *invert=bestStart;
                *clk=iii;
                return -1;
        }
        return bestErrCnt;
}
//translate wave to 11111100000 (1 for each short wave 0 for each long wave)
size_t fsk_wave_demod(uint8_t * dest, size_t size, uint8_t fchigh, uint8_t fclow)
{
        uint32_t last_transition = 0;
        uint32_t idx = 1;
        //uint32_t maxVal=0;
        if (fchigh==0) fchigh=10;
        if (fclow==0) fclow=8;
        //set the threshold close to 0 (graph) or 128 std to avoid static
        uint8_t threshold_value = 123; 

        // sync to first lo-hi transition, and threshold

        // Need to threshold first sample

        if(dest[0] < threshold_value) dest[0] = 0;
        else dest[0] = 1;

        size_t numBits = 0;
        // count cycles between consecutive lo-hi transitions, there should be either 8 (fc/8)
        // or 10 (fc/10) cycles but in practice due to noise etc we may end up with with anywhere
        // between 7 to 11 cycles so fuzz it by treat anything <9 as 8 and anything else as 10
        for(idx = 1; idx < size; idx++) {
                // threshold current value

                if (dest[idx] < threshold_value) dest[idx] = 0;
                else dest[idx] = 1;

                // Check for 0->1 transition
                if (dest[idx-1] < dest[idx]) { // 0 -> 1 transition
                        if ((idx-last_transition)<(fclow-2)){            //0-5 = garbage noise
                                //do nothing with extra garbage
                        } else if ((idx-last_transition) < (fchigh-1)) { //6-8 = 8 waves
                                dest[numBits]=1;
                        } else {                                                        //9+ = 10 waves
                                dest[numBits]=0;
                        }
                        last_transition = idx;
                        numBits++;
                }
        }
        return numBits; //Actually, it returns the number of bytes, but each byte represents a bit: 1 or 0
}

uint32_t myround2(float f)
{
        if (f >= 2000) return 2000;//something bad happened
        return (uint32_t) (f + (float)0.5);
}

//translate 11111100000 to 10
size_t aggregate_bits(uint8_t *dest, size_t size, uint8_t rfLen, uint8_t maxConsequtiveBits,
    uint8_t invert, uint8_t fchigh, uint8_t fclow)
{
        uint8_t lastval=dest[0];
        uint32_t idx=0;
        size_t numBits=0;
        uint32_t n=1;

        for( idx=1; idx < size; idx++) {

                if (dest[idx]==lastval) {
                        n++;
                        continue;
                }
                //if lastval was 1, we have a 1->0 crossing
                if ( dest[idx-1]==1 ) {
                        n=myround2((float)(n+1)/((float)(rfLen)/(float)fclow));
                } else {// 0->1 crossing
                        n=myround2((float)(n+1)/((float)(rfLen-1)/(float)fchigh));  //-1 for fudge factor
                }
                if (n == 0) n = 1;

                if(n < maxConsequtiveBits) //Consecutive
                {
                        if(invert==0){ //invert bits
                                memset(dest+numBits, dest[idx-1] , n);
                        }else{
                                memset(dest+numBits, dest[idx-1]^1 , n);
                        }
                        numBits += n;
                }
                n=0;
                lastval=dest[idx];
        }//end for
        return numBits;
}
//by marshmellow  (from holiman's base)
// full fsk demod from GraphBuffer wave to decoded 1s and 0s (no mandemod)
int fskdemod(uint8_t *dest, size_t size, uint8_t rfLen, uint8_t invert, uint8_t fchigh, uint8_t fclow)
{
        // FSK demodulator
        size = fsk_wave_demod(dest, size, fchigh, fclow);
        size = aggregate_bits(dest, size, rfLen, 192, invert, fchigh, fclow);
        return size;
}
// loop to get raw HID waveform then FSK demodulate the TAG ID from it
int HIDdemodFSK(uint8_t *dest, size_t *size, uint32_t *hi2, uint32_t *hi, uint32_t *lo)
{

        size_t idx=0, size2=*size, startIdx=0; 
        // FSK demodulator

        *size = fskdemod(dest, size2,50,0,10,8);

        // final loop, go over previously decoded manchester data and decode into usable tag ID
        // 111000 bit pattern represent start of frame, 01 pattern represents a 1 and 10 represents a 0
        uint8_t frame_marker_mask[] = {1,1,1,0,0,0};
        int numshifts = 0;
        idx = 0;
        //one scan
        while( idx + sizeof(frame_marker_mask) < *size) {
                // search for a start of frame marker
                if ( memcmp(dest+idx, frame_marker_mask, sizeof(frame_marker_mask)) == 0)
                { // frame marker found
                        startIdx=idx;
                        idx+=sizeof(frame_marker_mask);
                        while(dest[idx] != dest[idx+1] && idx < *size-2)
                        {
                                // Keep going until next frame marker (or error)
                                // Shift in a bit. Start by shifting high registers
                                *hi2 = (*hi2<<1)|(*hi>>31);
                                *hi = (*hi<<1)|(*lo>>31);
                                //Then, shift in a 0 or one into low
                                if (dest[idx] && !dest[idx+1])  // 1 0
                                        *lo=(*lo<<1)|0;
                                else // 0 1
                                        *lo=(*lo<<1)|1;
                                numshifts++;
                                idx += 2;
                        }
                        // Hopefully, we read a tag and  hit upon the next frame marker
                        if(idx + sizeof(frame_marker_mask) < *size)
                        {
                                if ( memcmp(dest+idx, frame_marker_mask, sizeof(frame_marker_mask)) == 0)
                                {
                                        //good return
                                        *size=idx-startIdx;
                                        return startIdx;
                                }
                        }
                        // reset
                        *hi2 = *hi = *lo = 0;
                        numshifts = 0;
                }else   {
                        idx++;
                }
        }
        return -1;
}

// loop to get raw paradox waveform then FSK demodulate the TAG ID from it
size_t ParadoxdemodFSK(uint8_t *dest, size_t *size, uint32_t *hi2, uint32_t *hi, uint32_t *lo)
{

        size_t idx=0, size2=*size;
        // FSK demodulator

        *size = fskdemod(dest, size2,50,1,10,8);

        // final loop, go over previously decoded manchester data and decode into usable tag ID
        // 00001111 bit pattern represent start of frame, 01 pattern represents a 1 and 10 represents a 0
        uint8_t frame_marker_mask[] = {0,0,0,0,1,1,1,1};
        uint16_t numshifts = 0;
        idx = 0;
        //one scan
        while( idx + sizeof(frame_marker_mask) < *size) {
                // search for a start of frame marker
                if ( memcmp(dest+idx, frame_marker_mask, sizeof(frame_marker_mask)) == 0)
                { // frame marker found
                        size2=idx;
                        idx+=sizeof(frame_marker_mask);
                        while(dest[idx] != dest[idx+1] && idx < *size-2)
                        {
                                // Keep going until next frame marker (or error)
                                // Shift in a bit. Start by shifting high registers
                                *hi2 = (*hi2<<1)|(*hi>>31);
                                *hi = (*hi<<1)|(*lo>>31);
                                //Then, shift in a 0 or one into low
                                if (dest[idx] && !dest[idx+1])  // 1 0
                                        *lo=(*lo<<1)|1;
                                else // 0 1
                                        *lo=(*lo<<1)|0;
                                numshifts++;
                                idx += 2;
                        }
                        // Hopefully, we read a tag and  hit upon the next frame marker and got enough bits
                        if(idx + sizeof(frame_marker_mask) < *size && numshifts > 40)
                        {
                                if ( memcmp(dest+idx, frame_marker_mask, sizeof(frame_marker_mask)) == 0)
                                {
                                        //good return - return start grid position and bits found
                                        *size = ((numshifts*2)+8);
                                        return size2;
                                }
                        }
                        // reset
                        *hi2 = *hi = *lo = 0;
                        numshifts = 0;
                }else   {
                        idx++;
                }
        }
        return 0;
}

uint32_t bytebits_to_byte(uint8_t* src, size_t numbits)
{
        uint32_t num = 0;
        for(int i = 0 ; i < numbits ; i++)
        {
                num = (num << 1) | (*src);
                src++;
        }
        return num;
}

int IOdemodFSK(uint8_t *dest, size_t size)
{
        static const uint8_t THRESHOLD = 129;
        uint32_t idx=0;
        //make sure buffer has data
        if (size < 66) return -1;
        //test samples are not just noise
        uint8_t justNoise = 1;
        for(idx=0;idx< size && justNoise ;idx++){
                justNoise = dest[idx] < THRESHOLD;
        }
        if(justNoise) return 0;

        // FSK demodulator
        size = fskdemod(dest, size, 64, 1, 10, 8);  //  RF/64 and invert
        if (size < 65) return -1;  //did we get a good demod?
        //Index map
        //0           10          20          30          40          50          60
        //|           |           |           |           |           |           |
        //01234567 8 90123456 7 89012345 6 78901234 5 67890123 4 56789012 3 45678901 23
        //-----------------------------------------------------------------------------
        //00000000 0 11110000 1 facility 1 version* 1 code*one 1 code*two 1 ???????? 11
        //
        //XSF(version)facility:codeone+codetwo
        //Handle the data
        uint8_t mask[] = {0,0,0,0,0,0,0,0,0,1};
        for( idx=0; idx < (size - 65); idx++) {
                if ( memcmp(dest + idx, mask, sizeof(mask))==0) {
                        //frame marker found
                        if (!dest[idx+8] && dest[idx+17]==1 && dest[idx+26]==1 && dest[idx+35]==1 && dest[idx+44]==1 && dest[idx+53]==1){
                                //confirmed proper separator bits found
                                //return start position
                                return (int) idx;
                        }
                }
        }
        return 0;
}

// by marshmellow
// pass bits to be tested in bits, length bits passed in bitLen, and parity type (even=0 | odd=1) in pType
// returns 1 if passed
uint8_t parityTest(uint32_t bits, uint8_t bitLen, uint8_t pType)
{
        uint8_t ans = 0;
        for (uint8_t i = 0; i < bitLen; i++){
                ans ^= ((bits >> i) & 1);
        }
  //PrintAndLog("DEBUG: ans: %d, ptype: %d",ans,pType);
        return (ans == pType);
}

// by marshmellow
// takes a array of binary values, start position, length of bits per parity (includes parity bit),
//   Parity Type (1 for odd 0 for even), and binary Length (length to run) 
size_t removeParity(uint8_t *BitStream, size_t startIdx, uint8_t pLen, uint8_t pType, size_t bLen)
{
        uint32_t parityWd = 0;
        size_t j = 0, bitCnt = 0;
        for (int word = 0; word < (bLen); word+=pLen){
                for (int bit=0; bit < pLen; bit++){
                        parityWd = (parityWd << 1) | BitStream[startIdx+word+bit];
      BitStream[j++] = (BitStream[startIdx+word+bit]);
                }
                j--;
                // if parity fails then return 0
                if (parityTest(parityWd, pLen, pType) == 0) return -1;
                bitCnt+=(pLen-1);
                parityWd = 0;
        }
        // if we got here then all the parities passed
        //return ID start index and size
        return bitCnt;
}

// by marshmellow
// FSK Demod then try to locate an AWID ID
int AWIDdemodFSK(uint8_t *dest, size_t size)
{
        static const uint8_t THRESHOLD = 123;
        uint32_t idx=0, idx2=0;
        //make sure buffer has data
        if (size < 96*50) return -1;
        //test samples are not just noise
        uint8_t justNoise = 1;
        for(idx=0; idx < size && justNoise ;idx++){
                justNoise = dest[idx] < THRESHOLD;
        }
        if(justNoise) return -2;

        // FSK demodulator
        size = fskdemod(dest, size, 50, 1, 10, 8);  //  RF/64 and invert
        if (size < 96) return -3;  //did we get a good demod?

        uint8_t mask[] = {0,0,0,0,0,0,0,1};
        for( idx=0; idx < (size - 96); idx++) {
                if ( memcmp(dest + idx, mask, sizeof(mask))==0) {
                        // frame marker found
                        //return ID start index
                        if (idx2 == 0) idx2=idx;
                        else if(idx-idx2==96) return idx2;
                        else return -5;

                        // should always get 96 bits if it is awid
                }
        }
        //never found mask
        return -4;
}

// by marshmellow
// FSK Demod then try to locate an Farpointe Data (pyramid) ID
int PyramiddemodFSK(uint8_t *dest, size_t size)
{
  static const uint8_t THRESHOLD = 123;
  uint32_t idx=0, idx2=0;
  // size_t size2 = size;
  //make sure buffer has data
  if (size < 128*50) return -5;
  //test samples are not just noise
  uint8_t justNoise = 1;
  for(idx=0; idx < size && justNoise ;idx++){
    justNoise = dest[idx] < THRESHOLD;
  }
  if(justNoise) return -1;

  // FSK demodulator
  size = fskdemod(dest, size, 50, 1, 10, 8);  //  RF/64 and invert
  if (size < 128) return -2;  //did we get a good demod?

  uint8_t mask[] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1};
  for( idx=0; idx < (size - 128); idx++) {
    if ( memcmp(dest + idx, mask, sizeof(mask))==0) {
      // frame marker found
      if (idx2==0) idx2=idx;
      else if (idx-idx2==128) return idx2;
      else return -3;
    }
  }
  //never found mask
  return -4;
}

// by marshmellow
// not perfect especially with lower clocks or VERY good antennas (heavy wave clipping)
// maybe somehow adjust peak trimming value based on samples to fix?
int DetectASKClock(uint8_t dest[], size_t size, int clock)
{
  int i=0;
  int clk[]={8,16,32,40,50,64,100,128,256};
  int loopCnt = 256;  //don't need to loop through entire array...
  if (size<loopCnt) loopCnt = size;

  //if we already have a valid clock quit
  
  for (;i<8;++i)
    if (clk[i] == clock) return clock;

  //get high and low peak
  int peak, low;
  getHiLo(dest, loopCnt, &peak, &low, 75, 75);
  
  int ii;
  int clkCnt;
  int tol = 0;
  int bestErr[]={1000,1000,1000,1000,1000,1000,1000,1000,1000};
  int errCnt=0;
  //test each valid clock from smallest to greatest to see which lines up
  for(clkCnt=0; clkCnt < 8; ++clkCnt){
    if (clk[clkCnt] == 32){
      tol=1;
    }else{
      tol=0;
    }
    bestErr[clkCnt]=1000;
    //try lining up the peaks by moving starting point (try first 256)
    for (ii=0; ii < loopCnt; ++ii){
      if ((dest[ii] >= peak) || (dest[ii] <= low)){
        errCnt=0;
        // now that we have the first one lined up test rest of wave array
        for (i=0; i<((int)((size-ii-tol)/clk[clkCnt])-1); ++i){
          if (dest[ii+(i*clk[clkCnt])]>=peak || dest[ii+(i*clk[clkCnt])]<=low){
          }else if(dest[ii+(i*clk[clkCnt])-tol]>=peak || dest[ii+(i*clk[clkCnt])-tol]<=low){
          }else if(dest[ii+(i*clk[clkCnt])+tol]>=peak || dest[ii+(i*clk[clkCnt])+tol]<=low){
          }else{  //error no peak detected
            errCnt++;
          }
        }
        //if we found no errors then we can stop here
        //  this is correct one - return this clock
            //PrintAndLog("DEBUG: clk %d, err %d, ii %d, i %d",clk[clkCnt],errCnt,ii,i);
        if(errCnt==0 && clkCnt<6) return clk[clkCnt];
        //if we found errors see if it is lowest so far and save it as best run
        if(errCnt<bestErr[clkCnt]) bestErr[clkCnt]=errCnt;
      }
    }
  }
  uint8_t iii=0;
  uint8_t best=0;
  for (iii=0; iii<8; ++iii){
    if (bestErr[iii]<bestErr[best]){
      if (bestErr[iii]==0) bestErr[iii]=1;
      // current best bit to error ratio     vs  new bit to error ratio
      if (((size/clk[best])/bestErr[best] < (size/clk[iii])/bestErr[iii]) ){
        best = iii;
      }
    }
  }
  return clk[best];
}

//by marshmellow
//detect psk clock by reading #peaks vs no peaks(or errors)
int DetectpskNRZClock(uint8_t dest[], size_t size, int clock)
{
        int i=0;
        int clk[]={16,32,40,50,64,100,128,256};
        int loopCnt = 2048;  //don't need to loop through entire array...
        if (size<loopCnt) loopCnt = size;

        //if we already have a valid clock quit
        for (; i < 7; ++i)
                if (clk[i] == clock) return clock;

        //get high and low peak
        int peak, low;
        getHiLo(dest, loopCnt, &peak, &low, 75, 75);

        //PrintAndLog("DEBUG: peak: %d, low: %d",peak,low);
        int ii;
        uint8_t clkCnt;
        uint8_t tol = 0;
        int peakcnt=0;
        int errCnt=0;
        int bestErr[]={1000,1000,1000,1000,1000,1000,1000,1000};
        int peaksdet[]={0,0,0,0,0,0,0,0};
        //test each valid clock from smallest to greatest to see which lines up
        for(clkCnt=0; clkCnt < 7; ++clkCnt){
                if (clk[clkCnt] <= 32){
                        tol=1;
                }else{
                        tol=0;
                }
                //try lining up the peaks by moving starting point (try first 256)
                for (ii=0; ii< loopCnt; ++ii){
                        if ((dest[ii] >= peak) || (dest[ii] <= low)){
                                errCnt=0;
                                peakcnt=0;
                                // now that we have the first one lined up test rest of wave array
                                for (i=0; i < ((int)((size-ii-tol)/clk[clkCnt])-1); ++i){
                                        if (dest[ii+(i*clk[clkCnt])]>=peak || dest[ii+(i*clk[clkCnt])]<=low){
                                                peakcnt++;
                                        }else if(dest[ii+(i*clk[clkCnt])-tol]>=peak || dest[ii+(i*clk[clkCnt])-tol]<=low){
                                                peakcnt++;
                                        }else if(dest[ii+(i*clk[clkCnt])+tol]>=peak || dest[ii+(i*clk[clkCnt])+tol]<=low){
                                                peakcnt++;
                                        }else{  //error no peak detected
                                                errCnt++;
                                        }
                                }
                                if(peakcnt>peaksdet[clkCnt]) {
                                        peaksdet[clkCnt]=peakcnt;
                                        bestErr[clkCnt]=errCnt;
                                }
                        }
                }
        }
        int iii=0;
        int best=0;
        //int ratio2;  //debug
        int ratio;
        //int bits;
        for (iii=0; iii < 7; ++iii){
                ratio=1000;
                //ratio2=1000;  //debug
                //bits=size/clk[iii];  //debug
                if (peaksdet[iii] > 0){
                        ratio=bestErr[iii]/peaksdet[iii];
                        if (((bestErr[best]/peaksdet[best]) > (ratio)+1)){
                                best = iii;
                        }
                        //ratio2=bits/peaksdet[iii]; //debug
                }
                //PrintAndLog("DEBUG: Clk: %d, peaks: %d, errs: %d, bestClk: %d, ratio: %d, bits: %d, peakbitr: %d",clk[iii],peaksdet[iii],bestErr[iii],clk[best],ratio, bits,ratio2);
        }
        return clk[best];
}

// by marshmellow (attempt to get rid of high immediately after a low)
void pskCleanWave(uint8_t *BitStream, size_t size)
{
        int i;
        int gap = 4;
        int newLow=0;
        int newHigh=0;
        int high, low;
        getHiLo(BitStream, size, &high, &low, 80, 90);
 
        for (i=0; i < size; ++i){
                if (newLow == 1){
                        if (BitStream[i]>low){
                                BitStream[i]=low+8;
                                gap--;
                        }
                        if (gap == 0){
                                newLow=0;
                                gap=4;
                        }
                }else if (newHigh == 1){
                        if (BitStream[i]<high){
                                BitStream[i]=high-8;
                                gap--;
                        }
                        if (gap == 0){
                                newHigh=0;
                                gap=4;
                        }
                }
                if (BitStream[i] <= low) newLow=1;
                if (BitStream[i] >= high) newHigh=1;
        }
        return;
}

// by marshmellow
// convert psk1 demod to psk2 demod
// only transition waves are 1s
void psk1TOpsk2(uint8_t *BitStream, size_t size)
{
        size_t i=1;
        uint8_t lastBit=BitStream[0];
        for (; i<size; i++){
                if (lastBit!=BitStream[i]){
                        lastBit=BitStream[i];
                        BitStream[i]=1;
                } else {
                        BitStream[i]=0;
                }
        }
        return;
}

// redesigned by marshmellow adjusted from existing decode functions
// indala id decoding - only tested on 26 bit tags, but attempted to make it work for more
int indala26decode(uint8_t *bitStream, size_t *size, uint8_t *invert)
{
        //26 bit 40134 format  (don't know other formats)
        int i;
        int long_wait=29;//29 leading zeros in format
        int start;
        int first = 0;
        int first2 = 0;
        int bitCnt = 0;
        int ii;
        // Finding the start of a UID
        for (start = 0; start <= *size - 250; start++) {
                first = bitStream[start];
                for (i = start; i < start + long_wait; i++) {
                        if (bitStream[i] != first) {
                                break;
                        }
                }
                if (i == (start + long_wait)) {
                        break;
                }
        }
        if (start == *size - 250 + 1) {
                // did not find start sequence
                return -1;
        }
        // Inverting signal if needed
        if (first == 1) {
                for (i = start; i < *size; i++) {
                        bitStream[i] = !bitStream[i];
                }
                *invert = 1;
        }else *invert=0;

        int iii;
        //found start once now test length by finding next one
        for (ii=start+29; ii <= *size - 250; ii++) {
                first2 = bitStream[ii];
                for (iii = ii; iii < ii + long_wait; iii++) {
                        if (bitStream[iii] != first2) {
                                break;
                        }
                }
                if (iii == (ii + long_wait)) {
                        break;
                }
        }
        if (ii== *size - 250 + 1){
                // did not find second start sequence
                return -2;
        }
        bitCnt=ii-start;

        // Dumping UID
        i = start;
        for (ii = 0; ii < bitCnt; ii++) {
                bitStream[ii] = bitStream[i++];
        }
        *size=bitCnt;
        return 1;
}

// by marshmellow - demodulate PSK1 wave or NRZ wave (both similar enough)
// peaks invert bit (high=1 low=0) each clock cycle = 1 bit determined by last peak
int pskNRZrawDemod(uint8_t *dest, size_t *size, int *clk, int *invert)
{
        pskCleanWave(dest,*size);
        int clk2 = DetectpskNRZClock(dest, *size, *clk);
        *clk=clk2;
        uint32_t i;
        int high, low, ans;
        ans = getHiLo(dest, 1260, &high, &low, 75, 80); //25% fuzz on high 20% fuzz on low
        if (ans<1) return -2; //just noise
        uint32_t gLen = *size;
        //PrintAndLog("DEBUG - valid high: %d - valid low: %d",high,low);
        int lastBit = 0;  //set first clock check
        uint32_t bitnum = 0;     //output counter
        uint8_t tol = 1;  //clock tolerance adjust - waves will be accepted as within the clock if they fall + or - this value + clock from last valid wave
        if (*clk==32) tol = 2;    //clock tolerance may not be needed anymore currently set to + or - 1 but could be increased for poor waves or removed entirely
        uint32_t iii = 0;
        uint8_t errCnt =0;
        uint32_t bestStart = *size;
        uint32_t maxErr = (*size/1000);
        uint32_t bestErrCnt = maxErr;
        uint8_t curBit=0;
        uint8_t bitHigh=0;
        uint8_t ignorewin=*clk/8;
        //PrintAndLog("DEBUG - lastbit - %d",lastBit);
        //loop to find first wave that works - align to clock
        for (iii=0; iii < gLen; ++iii){
                if ((dest[iii]>=high) || (dest[iii]<=low)){
                        lastBit=iii-*clk;
                        //loop through to see if this start location works
                        for (i = iii; i < *size; ++i) {
                                //if we found a high bar and we are at a clock bit
                                if ((dest[i]>=high ) && (i>=lastBit+*clk-tol && i<=lastBit+*clk+tol)){
                                        bitHigh=1;
                                        lastBit+=*clk;
                                        ignorewin=*clk/8;
                                        bitnum++;
                                //else if low bar found and we are at a clock point
                                }else if ((dest[i]<=low ) && (i>=lastBit+*clk-tol && i<=lastBit+*clk+tol)){
                                        bitHigh=1;
                                        lastBit+=*clk;
                                        ignorewin=*clk/8;
                                        bitnum++;
                                //else if no bars found
                                }else if(dest[i] < high && dest[i] > low) {
                                        if (ignorewin==0){
                                                bitHigh=0;
                                        }else ignorewin--;
                                                                                //if we are past a clock point
                                        if (i >= lastBit+*clk+tol){ //clock val
                                                lastBit+=*clk;
                                                bitnum++;
                                        }
                                //else if bar found but we are not at a clock bit and we did not just have a clock bit
                                }else if ((dest[i]>=high || dest[i]<=low) && (i<lastBit+*clk-tol || i>lastBit+*clk+tol) && (bitHigh==0)){
                                        //error bar found no clock...
                                        errCnt++;
                                }
                                if (bitnum>=1000) break;
                        }
                        //we got more than 64 good bits and not all errors
                        if ((bitnum > (64+errCnt)) && (errCnt < (maxErr))) {
                                //possible good read
                                if (errCnt == 0){
                                        bestStart = iii;
                                        bestErrCnt = errCnt;
                                        break;  //great read - finish
                                }
                                if (errCnt < bestErrCnt){  //set this as new best run
                                        bestErrCnt = errCnt;
                                        bestStart = iii;
                                }
                        }
                }
        }
        if (bestErrCnt < maxErr){
                //best run is good enough set to best run and set overwrite BinStream
                iii=bestStart;
                lastBit=bestStart-*clk;
                bitnum=0;
                for (i = iii; i < *size; ++i) {
                        //if we found a high bar and we are at a clock bit
                        if ((dest[i] >= high ) && (i>=lastBit+*clk-tol && i<=lastBit+*clk+tol)){
                                bitHigh=1;
                                lastBit+=*clk;
                                curBit=1-*invert;
                                dest[bitnum]=curBit;
                                ignorewin=*clk/8;
                                bitnum++;
                        //else if low bar found and we are at a clock point
                        }else if ((dest[i]<=low ) && (i>=lastBit+*clk-tol && i<=lastBit+*clk+tol)){
                                bitHigh=1;
                                lastBit+=*clk;
                                curBit=*invert;
                                dest[bitnum]=curBit;
                                ignorewin=*clk/8;
                                bitnum++;
                        //else if no bars found
                        }else if(dest[i]<high && dest[i]>low) {
                                if (ignorewin==0){
                                        bitHigh=0;
                                }else ignorewin--;
                                //if we are past a clock point
                                if (i>=lastBit+*clk+tol){ //clock val
                                        lastBit+=*clk;
                                        dest[bitnum]=curBit;
                                        bitnum++;
                                }
                        //else if bar found but we are not at a clock bit and we did not just have a clock bit
                        }else if ((dest[i]>=high || dest[i]<=low) && ((i<lastBit+*clk-tol) || (i>lastBit+*clk+tol)) && (bitHigh==0)){
                                //error bar found no clock...
                                bitHigh=1;
                                dest[bitnum]=77;
                                bitnum++;
                                errCnt++;
                        }
                        if (bitnum >=1000) break;
                }
                *size=bitnum;
        } else{
                *size=bitnum;
                *clk=bestStart;
                return -1;
        }

        if (bitnum>16){
                *size=bitnum;
        } else return -1;
        return errCnt;
}

//by marshmellow
//detects the bit clock for FSK given the high and low Field Clocks
uint8_t detectFSKClk(uint8_t *BitStream, size_t size, uint8_t fcHigh, uint8_t fcLow)
{
  uint8_t clk[] = {8,16,32,40,50,64,100,128,0};
  uint16_t rfLens[] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
  uint8_t rfCnts[] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
  uint8_t rfLensFnd = 0;
  uint8_t lastFCcnt=0;
  uint32_t fcCounter = 0;
  uint16_t rfCounter = 0;
  uint8_t firstBitFnd = 0;
  size_t i;

  uint8_t fcTol = (uint8_t)(0.5+(float)(fcHigh-fcLow)/2);
  rfLensFnd=0;
  fcCounter=0;
  rfCounter=0;
  firstBitFnd=0;
  //PrintAndLog("DEBUG: fcTol: %d",fcTol);
  // prime i to first up transition
  for (i = 1; i < size-1; i++)
    if (BitStream[i] > BitStream[i-1] && BitStream[i]>=BitStream[i+1])
      break;

  for (; i < size-1; i++){
    if (BitStream[i] > BitStream[i-1] && BitStream[i]>=BitStream[i+1]){
      // new peak 
      fcCounter++;
      rfCounter++;
      // if we got less than the small fc + tolerance then set it to the small fc
      if (fcCounter < fcLow+fcTol) 
        fcCounter = fcLow;
      else //set it to the large fc
        fcCounter = fcHigh;
     
      //look for bit clock  (rf/xx)
      if ((fcCounter<lastFCcnt || fcCounter>lastFCcnt)){
        //not the same size as the last wave - start of new bit sequence

        if (firstBitFnd>1){ //skip first wave change - probably not a complete bit
          for (int ii=0; ii<15; ii++){
            if (rfLens[ii]==rfCounter){
              rfCnts[ii]++;
              rfCounter=0;
              break;
            }
          }
          if (rfCounter>0 && rfLensFnd<15){
            //PrintAndLog("DEBUG: rfCntr %d, fcCntr %d",rfCounter,fcCounter);
            rfCnts[rfLensFnd]++;
            rfLens[rfLensFnd++]=rfCounter;
          }
        } else {
          firstBitFnd++;
        }
        rfCounter=0;
        lastFCcnt=fcCounter;
      }
      fcCounter=0;
    } else {
      // count sample
      fcCounter++;
      rfCounter++;
    }
  }
  uint8_t rfHighest=15, rfHighest2=15, rfHighest3=15;

  for (i=0; i<15; i++){
    //PrintAndLog("DEBUG: RF %d, cnts %d",rfLens[i], rfCnts[i]);
    //get highest 2 RF values  (might need to get more values to compare or compare all?)
    if (rfCnts[i]>rfCnts[rfHighest]){
      rfHighest3=rfHighest2;
      rfHighest2=rfHighest;
      rfHighest=i;
    } else if(rfCnts[i]>rfCnts[rfHighest2]){
      rfHighest3=rfHighest2;
      rfHighest2=i;
    } else if(rfCnts[i]>rfCnts[rfHighest3]){
      rfHighest3=i;
    }
  }  
  // set allowed clock remainder tolerance to be 1 large field clock length+1 
  //   we could have mistakenly made a 9 a 10 instead of an 8 or visa versa so rfLens could be 1 FC off  
  uint8_t tol1 = fcHigh+1; 
  
  //PrintAndLog("DEBUG: hightest: 1 %d, 2 %d, 3 %d",rfLens[rfHighest],rfLens[rfHighest2],rfLens[rfHighest3]);

  // loop to find the highest clock that has a remainder less than the tolerance
  //   compare samples counted divided by
  int ii=7;
  for (; ii>=0; ii--){
    if (rfLens[rfHighest] % clk[ii] < tol1 || rfLens[rfHighest] % clk[ii] > clk[ii]-tol1){
      if (rfLens[rfHighest2] % clk[ii] < tol1 || rfLens[rfHighest2] % clk[ii] > clk[ii]-tol1){
        if (rfLens[rfHighest3] % clk[ii] < tol1 || rfLens[rfHighest3] % clk[ii] > clk[ii]-tol1){
          break;
        }
      }
    }
  }

  if (ii<0) return 0; // oops we went too far

  return clk[ii];
}

//by marshmellow
//countFC is to detect the field clock lengths.
//counts and returns the 2 most common wave lengths
uint16_t countFC(uint8_t *BitStream, size_t size)
{
  uint8_t fcLens[] = {0,0,0,0,0,0,0,0,0,0};
  uint16_t fcCnts[] = {0,0,0,0,0,0,0,0,0,0};
  uint8_t fcLensFnd = 0;
  uint8_t lastFCcnt=0;
  uint32_t fcCounter = 0;
  size_t i;
  
  // prime i to first up transition
  for (i = 1; i < size-1; i++)
    if (BitStream[i] > BitStream[i-1] && BitStream[i] >= BitStream[i+1])
      break;

  for (; i < size-1; i++){
    if (BitStream[i] > BitStream[i-1] && BitStream[i] >= BitStream[i+1]){
        // new up transition
        fcCounter++;
        
      //if we had 5 and now have 9 then go back to 8 (for when we get a fc 9 instead of an 8)
      if (lastFCcnt==5 && fcCounter==9) fcCounter--;
      //if odd and not rc/5 add one (for when we get a fc 9 instead of 10)
      if ((fcCounter==9 && fcCounter & 1) || fcCounter==4) fcCounter++;

      // save last field clock count  (fc/xx)
      // find which fcLens to save it to:
      for (int ii=0; ii<10; ii++){
        if (fcLens[ii]==fcCounter){
          fcCnts[ii]++;
          fcCounter=0;
          break;
        }
      }
      if (fcCounter>0 && fcLensFnd<10){
        //add new fc length 
        fcCnts[fcLensFnd]++;
        fcLens[fcLensFnd++]=fcCounter;
      }
      fcCounter=0;
    } else {
      // count sample
      fcCounter++;
    }
  }
  
  uint8_t best1=9, best2=9, best3=9;
  uint16_t maxCnt1=0;
  // go through fclens and find which ones are bigest 2  
  for (i=0; i<10; i++){
    // PrintAndLog("DEBUG: FC %d, Cnt %d, Errs %d",fcLens[i],fcCnts[i],errCnt);    
    // get the 3 best FC values
    if (fcCnts[i]>maxCnt1) {
      best3=best2;
      best2=best1;
      maxCnt1=fcCnts[i];
      best1=i;
    } else if(fcCnts[i]>fcCnts[best2]){
      best3=best2;
      best2=i;
    } else if(fcCnts[i]>fcCnts[best3]){
      best3=i;
    }
  }
  uint8_t fcH=0, fcL=0;
  if (fcLens[best1]>fcLens[best2]){
    fcH=fcLens[best1];
    fcL=fcLens[best2];
  } else{
    fcH=fcLens[best2];
    fcL=fcLens[best1];
  }
 
  // TODO: take top 3 answers and compare to known Field clocks to get top 2

  uint16_t fcs = (((uint16_t)fcH)<<8) | fcL;
  // PrintAndLog("DEBUG: Best %d  best2 %d best3 %d",fcLens[best1],fcLens[best2],fcLens[best3]);
  
  return fcs;
}