Updated the CHANGELOG.md with things that I've been fiddeling with.

[proxmark3-svn] / common / crc16.c

diff --git a/common/crc16.c b/common/crc16.c
index a04c40127c82a996cff60985c1650ca629772c19..c90eeb558b22cbb5fb6addf37ea90ac0886f145a 100644 (file)
--- a/common/crc16.c
+++ b/common/crc16.c
@@ -7,7 +7,8 @@
 //-----------------------------------------------------------------------------
 
 #include "crc16.h"
-
+#define CRC16_POLY_CCITT 0x1021
+#define CRC16_POLY 0x8408
 
 unsigned short update_crc16( unsigned short crc, unsigned char c )
 {
@@ -15,11 +16,11 @@ unsigned short update_crc16( unsigned short crc, unsigned char c )
 
   v = (crc ^ c) & 0xff;
   for (i = 0; i < 8; i++) {
-      tcrc = ( (tcrc ^ v) & 1 ) ? ( tcrc >> 1 ) ^ 0x8408 : tcrc >> 1;
+      tcrc = ( (tcrc ^ v) & 1 ) ? ( tcrc >> 1 ) ^ CRC16_POLY : tcrc >> 1;
       v >>= 1;
   }
 
-  return ((crc >> 8) ^ tcrc)&0xffff;
+  return ((crc >> 8) ^ tcrc) & 0xffff;
 }
 
 uint16_t crc16(uint8_t const *message, int length, uint16_t remainder, uint16_t polynomial) {
@@ -41,9 +42,22 @@ uint16_t crc16(uint8_t const *message, int length, uint16_t remainder, uint16_t
 }
 
 uint16_t crc16_ccitt(uint8_t const *message, int length) {
-    return crc16(message, length, 0xffff, 0x1021);
+    return crc16(message, length, 0xffff, CRC16_POLY_CCITT);
 }
 
-uint16_t crc16_ccitt_rev(uint8_t const *message, int length) {
-    return crc16(message, length, 0x0000, 0x1021);
-}
\ No newline at end of file
+uint16_t crc16_ccitt_kermit(uint8_t const *message, int length) {
+    return bit_reverse_uint16(crc16(message, length, 0x0000, CRC16_POLY_CCITT));
+}
+uint16_t bit_reverse_uint16 (uint16_t value) {
+       const uint16_t mask0 = 0x5555;
+       const uint16_t mask1 = 0x3333;
+       const uint16_t mask2 = 0x0F0F;
+       const uint16_t mask3 = 0x00FF;
+
+       value = (((~mask0) & value) >> 1) | ((mask0 & value) << 1);
+       value = (((~mask1) & value) >> 2) | ((mask1 & value) << 2);
+       value = (((~mask2) & value) >> 4) | ((mask2 & value) << 4);
+       value = (((~mask3) & value) >> 8) | ((mask3 & value) << 8);
+
+       return value;
+}