X-Git-Url: https://git.zerfleddert.de/cgi-bin/gitweb.cgi/proxmark3-svn/blobdiff_plain/bd20f8f47847787e1f3e933043933272908c5beb..bc3b2f7f9422d8d112b48fa46c0d3fa8446285ec:/common/crc16.c?ds=inline diff --git a/common/crc16.c b/common/crc16.c index d181bb2a..a37f1d7e 100644 --- a/common/crc16.c +++ b/common/crc16.c @@ -10,13 +10,52 @@ 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; +} + +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; + + 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; }