X-Git-Url: https://git.zerfleddert.de/cgi-bin/gitweb.cgi/proxmark3-svn/blobdiff_plain/6eaa8da9dcc7543194435f706c72272783331df7..refs/pull/538/head:/common/crc16.c diff --git a/common/crc16.c b/common/crc16.c index d48df3b2..a37f1d7e 100644 --- a/common/crc16.c +++ b/common/crc16.c @@ -8,7 +8,6 @@ #include "crc16.h" - unsigned short update_crc16( unsigned short crc, unsigned char c ) { unsigned short i, v, tcrc = 0; @@ -44,16 +43,19 @@ uint16_t crc16_ccitt(uint8_t const *message, int length) { } 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, 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; + + 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; }