Diff: crc.c

Revision:

0:e4dad9e53f06

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/crc.c	Wed Nov 04 09:58:41 2015 +0000
@@ -0,0 +1,23 @@
+#include "crc.h"
+
+void crc8_calculate_byte_streaming(const uint8_t data, uint8_t *crc) {
+  // Optimal polynomial chosen based on
+  // http://users.ece.cmu.edu/~koopman/roses/dsn04/koopman04_crc_poly_embedded.pdf
+  // Note that this is different than the standard CRC-8 polynomial, because the
+  // standard CRC-8 polynomial is not particularly good.
+
+  // nibble lookup table for (x^8 + x^5 + x^3 + x^2 + x + 1)
+  static const uint8_t lookup_table[] =
+      { 0, 47, 94, 113, 188, 147, 226, 205, 87, 120, 9, 38, 235, 196,
+        181, 154 };
+
+  int i;
+  for (i = 2; i > 0; i--) {
+    uint8_t nibble = data;
+    if (i % 2 == 0) {
+      nibble >>= 4;
+    }
+    int index = nibble ^ (*crc >> 4);
+    *crc = lookup_table[index & 0xf] ^ (*crc << 4);
+  }
+}