mbed-mruby

Diff: src/crc.c

Revision:

0:158c61bb030f

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/crc.c	Wed Mar 25 17:36:16 2015 +0000
@@ -0,0 +1,40 @@
+/*
+** crc.c - calculate CRC
+**
+** See Copyright Notice in mruby.h
+*/
+
+#include <limits.h>
+#include <stdint.h>
+#include <stddef.h>
+
+/* Calculate CRC (CRC-16-CCITT)
+**
+**  0000_0000_0000_0000_0000_0000_0000_0000
+**          ^|------- CRC -------|- work --|
+**        carry
+*/
+#define  CRC_16_CCITT       0x11021ul        /* x^16+x^12+x^5+1 */
+#define  CRC_XOR_PATTERN    (CRC_16_CCITT << 8)
+#define  CRC_CARRY_BIT      (0x01000000)
+
+uint16_t
+calc_crc_16_ccitt(const uint8_t *src, size_t nbytes, uint16_t crc)
+{
+  size_t ibyte;
+  uint32_t ibit;
+  uint32_t crcwk = crc << 8;
+
+  for (ibyte = 0; ibyte < nbytes; ibyte++) {
+    crcwk |= *src++;
+    for (ibit = 0; ibit < CHAR_BIT; ibit++) {
+      crcwk <<= 1;
+      if (crcwk & CRC_CARRY_BIT) {
+        crcwk ^= CRC_XOR_PATTERN;
+      }
+    }
+  }
+  return (uint16_t)(crcwk >> 8);
+}
+
+