X-Git-Url: https://git.zerfleddert.de/cgi-bin/gitweb.cgi/proxmark3-svn/blobdiff_plain/6eaa8da9dcc7543194435f706c72272783331df7..e994394a40ad9c7b8e33e2fed3357d5d91ab2709:/common/crc16.c

diff --git a/common/crc16.c b/common/crc16.c
index d48df3b2..07090fc6 100644
--- a/common/crc16.c
+++ b/common/crc16.c
@@ -7,53 +7,56 @@
 //-----------------------------------------------------------------------------
 
 #include "crc16.h"
-
+#define CRC16_MASK_CCITT 0x1021
 
 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;
-	}
+  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;
+  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;
+    
+	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);
+    return crc16(message, length, 0xffff, CRC16_MASK_CCITT);
 }
 
 uint16_t crc16_ccitt_kermit(uint8_t const *message, int length) {
-	if (length == 0) return 0;
-	uint32_t crc = 0, q = 0;
-	uint8_t c;
-
-	for (int i = 0; i < length; i++){
-		c = message[i];
-		q = (crc ^ c ) & 0xF;
-		crc = (crc >> 4) ^ (q * 0x1081);
-		q = (crc ^ (c >> 4)) & 0xF;
-		crc = (crc >> 4) ^ (q * 0x1081);
-	}
-	return crc;
+    return bit_reverse_uint16(crc16(message, length, 0x0000, CRC16_MASK_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;
 }