X-Git-Url: https://git.zerfleddert.de/cgi-bin/gitweb.cgi/proxmark3-svn/blobdiff_plain/fdcc61d3189f7e91db27a865c25d923849ec47d5..8b5ec1f4a68e86ae1bffe965d3e131ad709b75fc:/common/crc16.c

diff --git a/common/crc16.c b/common/crc16.c
index 4225ceb1..a37f1d7e 100644
--- a/common/crc16.c
+++ b/common/crc16.c
@@ -1,14 +1,61 @@
+//-----------------------------------------------------------------------------
+// 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.
+//-----------------------------------------------------------------------------
+// CRC16
+//-----------------------------------------------------------------------------
+
 #include "crc16.h"
 
 unsigned short update_crc16( unsigned short crc, unsigned char c )
 {
-  unsigned short i, v, tcrc = 0;
+	unsigned short i, v, tcrc = 0;
+
+	v = (crc ^ c) & 0xff;
+	for (i = 0; i < 8; i++) {
+		tcrc = ( (tcrc ^ v) & 1 ) ? ( tcrc >> 1 ) ^ 0x8408 : tcrc >> 1;
+		v >>= 1;
+	}
+
+	return ((crc >> 8) ^ tcrc)&0xffff;
+}
+
+uint16_t crc16(uint8_t const *message, int length, uint16_t remainder, uint16_t polynomial) {
+
+	if (length == 0) return (~remainder);
+
+	for (int byte = 0; byte < length; ++byte) {
+		remainder ^= (message[byte] << 8);
+		for (uint8_t bit = 8; bit > 0; --bit) {
+			if (remainder & 0x8000) {
+				remainder = (remainder << 1) ^ polynomial;
+			} else {
+				remainder = (remainder << 1);
+			}
+		}
+	}
+	return remainder;
+}
+
+uint16_t crc16_ccitt(uint8_t const *message, int length) {
+	return crc16(message, length, 0xffff, 0x1021);
+}
+
+uint16_t crc16_ccitt_kermit(uint8_t const *message, int length) {
+	return bit_reverse_uint16(crc16(message, length, 0x0000, 0x1021));
+}
+
+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;
 
-  v = (crc ^ c) & 0xff;
-  for (i = 0; i < 8; i++) {
-      tcrc = ( (tcrc ^ v) & 1 ) ? ( tcrc >> 1 ) ^ 0x8408 : tcrc >> 1;
-      v >>= 1;
-  }
+	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 ((crc >> 8) ^ tcrc)&0xffff;
+	return value;
 }