Diff: crc.cpp

Revision:

0:c4676d32d381

Child:

1:aaffeb93f99b

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/crc.cpp	Tue Sep 15 15:27:55 2015 +0000
@@ -0,0 +1,130 @@
+// From : http://stackoverflow.com/questions/15169387/definitive-crc-for-c
+/* 8-bit CRC with polynomial x^8+x^6+x^3+x^2+1, 0x14D.
+   Chosen based on Koopman, et al. (0xA6 in his notation = 0x14D >> 1):
+   http://www.ece.cmu.edu/~koopman/roses/dsn04/koopman04_crc_poly_embedded.pdf
+ */
+
+#include "crc.h"
+/*
+static const unsigned char crc8_table[] = {
+    0x00, 0x3e, 0x7c, 0x42, 0xf8, 0xc6, 0x84, 0xba, 0x95, 0xab, 0xe9, 0xd7,
+    0x6d, 0x53, 0x11, 0x2f, 0x4f, 0x71, 0x33, 0x0d, 0xb7, 0x89, 0xcb, 0xf5,
+    0xda, 0xe4, 0xa6, 0x98, 0x22, 0x1c, 0x5e, 0x60, 0x9e, 0xa0, 0xe2, 0xdc,
+    0x66, 0x58, 0x1a, 0x24, 0x0b, 0x35, 0x77, 0x49, 0xf3, 0xcd, 0x8f, 0xb1,
+    0xd1, 0xef, 0xad, 0x93, 0x29, 0x17, 0x55, 0x6b, 0x44, 0x7a, 0x38, 0x06,
+    0xbc, 0x82, 0xc0, 0xfe, 0x59, 0x67, 0x25, 0x1b, 0xa1, 0x9f, 0xdd, 0xe3,
+    0xcc, 0xf2, 0xb0, 0x8e, 0x34, 0x0a, 0x48, 0x76, 0x16, 0x28, 0x6a, 0x54,
+    0xee, 0xd0, 0x92, 0xac, 0x83, 0xbd, 0xff, 0xc1, 0x7b, 0x45, 0x07, 0x39,
+    0xc7, 0xf9, 0xbb, 0x85, 0x3f, 0x01, 0x43, 0x7d, 0x52, 0x6c, 0x2e, 0x10,
+    0xaa, 0x94, 0xd6, 0xe8, 0x88, 0xb6, 0xf4, 0xca, 0x70, 0x4e, 0x0c, 0x32,
+    0x1d, 0x23, 0x61, 0x5f, 0xe5, 0xdb, 0x99, 0xa7, 0xb2, 0x8c, 0xce, 0xf0,
+    0x4a, 0x74, 0x36, 0x08, 0x27, 0x19, 0x5b, 0x65, 0xdf, 0xe1, 0xa3, 0x9d,
+    0xfd, 0xc3, 0x81, 0xbf, 0x05, 0x3b, 0x79, 0x47, 0x68, 0x56, 0x14, 0x2a,
+    0x90, 0xae, 0xec, 0xd2, 0x2c, 0x12, 0x50, 0x6e, 0xd4, 0xea, 0xa8, 0x96,
+    0xb9, 0x87, 0xc5, 0xfb, 0x41, 0x7f, 0x3d, 0x03, 0x63, 0x5d, 0x1f, 0x21,
+    0x9b, 0xa5, 0xe7, 0xd9, 0xf6, 0xc8, 0x8a, 0xb4, 0x0e, 0x30, 0x72, 0x4c,
+    0xeb, 0xd5, 0x97, 0xa9, 0x13, 0x2d, 0x6f, 0x51, 0x7e, 0x40, 0x02, 0x3c,
+    0x86, 0xb8, 0xfa, 0xc4, 0xa4, 0x9a, 0xd8, 0xe6, 0x5c, 0x62, 0x20, 0x1e,
+    0x31, 0x0f, 0x4d, 0x73, 0xc9, 0xf7, 0xb5, 0x8b, 0x75, 0x4b, 0x09, 0x37,
+    0x8d, 0xb3, 0xf1, 0xcf, 0xe0, 0xde, 0x9c, 0xa2, 0x18, 0x26, 0x64, 0x5a,
+    0x3a, 0x04, 0x46, 0x78, 0xc2, 0xfc, 0xbe, 0x80, 0xaf, 0x91, 0xd3, 0xed,
+    0x57, 0x69, 0x2b, 0x15};
+
+unsigned crc8(unsigned char *data, uint16_t len)
+{
+	static unsigned char crc;
+    unsigned char *end;
+
+    if (len == 0)
+        return crc;
+
+    crc ^= 0xff;
+    end = data + len;
+    do {
+        crc = crc8_table[crc ^ *data++];
+    } while (data < end);
+    return crc ^ 0xff;
+	return 0;
+}*/
+
+/* this was used to generate the table and to test the table-version
+
+#define POLY 0xB2
+
+unsigned crc8_slow(unsigned crc, unsigned char *data, size_t len)
+{
+    unsigned char *end;
+
+    if (len == 0)
+        return crc;
+    crc ^= 0xff;
+    end = data + len;
+    do {
+        crc ^= *data++;
+        crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1;
+        crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1;
+        crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1;
+        crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1;
+        crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1;
+        crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1;
+        crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1;
+        crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1;
+    } while (data < end);
+    return crc ^ 0xff;
+}
+*/
+/*
+# From : https://en.wikipedia.org/wiki/Computation_of_cyclic_redundancy_checks
+
+# Most significant bit first (big-endian)
+# x^16+x^12+x^5+1 = (1) 0001 0000 0010 0001 = 0x1021
+
+def crc16(data):
+    rem  = 0
+    n = 16
+    # A popular variant complements rem here
+    for d in data:
+        rem  = rem ^ (d << (n-8))   # n = 16 in this example
+        for j in range(1,8):
+            # Assuming 8 bits per byte
+            if rem & 0x8000:
+            # if leftmost (most significant) bit is set
+                rem  = (rem << 1) ^ 0x1021
+            else:
+                rem  = rem << 1
+        rem  = rem & 0xffff      # Trim remainder to 16 bits
+    # A popular variant complements rem here
+    return rem
+*/
+// Most significant bit first (big-endian)
+// x^16+x^12+x^5+1 = (1) 0001 0000 0010 0001 = 0x1021
+
+uint16_t crc16(uint8_t* data, uint16_t len)
+{
+	uint16_t rem  = 0;
+	uint16_t n = 16;
+	// A popular variant complements rem here
+	for(uint16_t i = 0 ; i < len ; i++)
+	{
+		rem  = rem ^ (data[i] << (n-8));   // n = 16 in this example
+
+		for(uint16_t j = 1 ; j < 8 ; j++)  // Assuming 8 bits per byte
+		{
+
+			if(rem & 0x8000)
+			{
+				// if leftmost (most significant) bit is set
+				rem  = (rem << 1) ^ 0x1021;
+			}
+			else
+			{
+				rem  = rem << 1;
+			}
+		 rem  &= 0xffff;      // Trim remainder to 16 bits
+		}
+	}
+ // A popular variant complements rem here
+  return rem;
+ }
+
+