Add CCITT Kermit CRC check for FDX-B demod

[proxmark3-svn] / common / crc16.c

diff --git a/common/crc16.c b/common/crc16.c
index 973cd103c009b16697b7523b1cbf60b107500f7a..d48df3b2c9f650720c1a4c39810010ce4f8ded44 100644 (file)
--- a/common/crc16.c
+++ b/common/crc16.c
@@ -11,35 +11,49 @@
 
 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, 0x1021);
+}
+
+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;
 }