Merge pull request #801 from sdb4/feat_support_rolling_crc

support for rolling crc16

Author: vedderb

util/crc.c

@@ -53,14 +53,17 @@ const unsigned short crc16_tab[] = { 0x0000, 0x1021, 0x2042, 0x3063, 0x4084,
 		0x0cc1, 0xef1f, 0xff3e, 0xcf5d, 0xdf7c, 0xaf9b, 0xbfba, 0x8fd9, 0x9ff8,
 		0x6e17, 0x7e36, 0x4e55, 0x5e74, 0x2e93, 0x3eb2, 0x0ed1, 0x1ef0 };
 
-unsigned short crc16(unsigned char *buf, unsigned int len) {
-	unsigned short cksum = 0;
+unsigned short crc16_rolling(unsigned short cksum, unsigned char *buf, unsigned int len) {
 	for (unsigned int i = 0; i < len; i++) {
 		cksum = crc16_tab[(((cksum >> 8) ^ *buf++) & 0xFF)] ^ (cksum << 8);
 	}
 	return cksum;
 }
 
+unsigned short crc16(unsigned char *buf, unsigned int len) {
+	return crc16_rolling(0, buf, len);
+}
+
 #ifndef NO_STM32
 /**
   * @brief  Computes the 32-bit CRC of a given buffer of data word(32-bit) using

util/crc.h

@@ -25,6 +25,7 @@
 /*
  * Functions
  */
+unsigned short crc16_rolling(unsigned short cksum, unsigned char *buf, unsigned int len);
 unsigned short crc16(unsigned char *buf, unsigned int len);
 uint32_t crc32(uint32_t *buf, uint32_t len);
 void crc32_reset(void);