1 files changed, 37 insertions, 0 deletions
diff --git a/reference/C/CONTRIB/SNIP/crc-16.c b/reference/C/CONTRIB/SNIP/crc-16.c
new file mode 100755
index 0000000..e1f3165
--- /dev/null
+++ b/reference/C/CONTRIB/SNIP/crc-16.c
@@ -0,0 +1,37 @@
+#define POLY 0x8408
+/*
+//                                      16   12   5
+// this is the CCITT CRC 16 polynomial X  + X  + X  + 1.
+// This works out to be 0x1021, but the way the algorithm works
+// lets us use 0x8408 (the reverse of the bit pattern).  The high
+// bit is always assumed to be set, thus we only use 16 bits to
+// represent the 17 bit value.
+*/
+
+unsigned short crc16(char *data_p, unsigned short length)
+{
+      unsigned char i;
+      unsigned int data;
+      unsigned int crc = 0xffff;
+
+      if (length == 0)
+            return (~crc);
+
+      do
+      {
+            for (i=0, data=(unsigned int)0xff & *data_p++;
+                 i < 8; 
+                 i++, data >>= 1)
+            {
+                  if ((crc & 0x0001) ^ (data & 0x0001))
+                        crc = (crc >> 1) ^ POLY;
+                  else  crc >>= 1;
+            }
+      } while (--length);
+
+      crc = ~crc;
+      data = crc;
+      crc = (crc << 8) | (data >> 8 & 0xff);
+
+      return (crc);
+}