ADD: @marshmello42 's fixes for low frequency demodulation lengths greater the 512bits.

[proxmark3-svn] / common / crc16.c

diff --git a/common/crc16.c b/common/crc16.c
index d48df3b2c9f650720c1a4c39810010ce4f8ded44..07090fc6fbbeec4f56300dbb6246c4a5adf74041 100644 (file)
--- 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;
 }