X-Git-Url: https://git.zerfleddert.de/cgi-bin/gitweb.cgi/proxmark3-svn/blobdiff_plain/23b80a733436e88426c2b857950674768eb2b8a2..6bb7609cadc5868663fea41064779b767c6e382f:/common/crc16.c

diff --git a/common/crc16.c b/common/crc16.c
index 973cd103..c90eeb55 100644
--- 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) {
@@ -41,5 +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_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;
 }