Diff: source/daplink/crc16.c

Revision:

0:01f31e923fe2

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/source/daplink/crc16.c	Tue Apr 07 12:55:42 2020 +0200
@@ -0,0 +1,144 @@
+/**********************************************************************
+ *
+ * Filename:    crc.c
+ *
+ * Description: Slow and fast implementations of the CRC standards.
+ *
+ * Notes:       The parameters for each supported CRC standard are
+ *				defined in the header file crc.h.  The implementations
+ *				here should stand up to further additions to that list.
+ *
+ *
+ * Copyright (c) 2000 by Michael Barr.  This software is placed into
+ * the public domain and may be used for any purpose.  However, this
+ * notice must not be changed or removed and no warranty is either
+ * expressed or implied by its publication or distribution.
+ **********************************************************************/
+
+/**
+ * @file    crc16.c
+ * @brief   Implementation of crc.h
+ */
+
+#include "crc.h"
+
+#define FALSE	0
+#define TRUE	!FALSE
+
+typedef unsigned short  crc;
+
+#define CRC_NAME			"CRC-16"
+#define POLYNOMIAL			0x8005
+#define INITIAL_REMAINDER	0x0000
+#define FINAL_XOR_VALUE		0x0000
+#define REFLECT_DATA		TRUE
+#define REFLECT_REMAINDER	TRUE
+#define CHECK_VALUE			0xBB3D
+
+/*
+ * Derive parameters from the standard-specific parameters in crc.h.
+ */
+#define WIDTH    (8 * sizeof(crc))
+#define TOPBIT   (1 << (WIDTH - 1))
+
+#if (REFLECT_DATA == TRUE)
+#undef  REFLECT_DATA
+#define REFLECT_DATA(X)			((unsigned char) reflect((X), 8))
+#else
+#undef  REFLECT_DATA
+#define REFLECT_DATA(X)			(X)
+#endif
+
+#if (REFLECT_REMAINDER == TRUE)
+#undef  REFLECT_REMAINDER
+#define REFLECT_REMAINDER(X)	((crc) reflect((X), WIDTH))
+#else
+#undef  REFLECT_REMAINDER
+#define REFLECT_REMAINDER(X)	(X)
+#endif
+
+
+/*********************************************************************
+ *
+ * Function:    reflect()
+ *
+ * Description: Reorder the bits of a binary sequence, by reflecting
+ *				them about the middle position.
+ *
+ * Notes:		No checking is done that nBits <= 32.
+ *
+ * Returns:		The reflection of the original data.
+ *
+ *********************************************************************/
+static unsigned long
+reflect(unsigned long data, unsigned char nBits)
+{
+    unsigned long  reflection = 0x00000000;
+    unsigned char  bit;
+
+    /*
+     * Reflect the data about the center bit.
+     */
+    for (bit = 0; bit < nBits; ++bit) {
+        /*
+         * If the LSB bit is set, set the reflection of it.
+         */
+        if (data & 0x01) {
+            reflection |= (1 << ((nBits - 1) - bit));
+        }
+
+        data = (data >> 1);
+    }
+
+    return (reflection);
+}	/* reflect() */
+
+
+/*********************************************************************
+ *
+ * Function:    crcSlow()
+ *
+ * Description: Compute the CRC of a given message.
+ *
+ * Notes:
+ *
+ * Returns:		The CRC of the message.
+ *
+ *********************************************************************/
+uint16_t
+crc16(const void *data, int nBytes)
+{
+    crc            remainder = INITIAL_REMAINDER;
+    int            byte;
+    unsigned char  bit;
+    unsigned char const *message = data;
+
+    /*
+     * Perform modulo-2 division, a byte at a time.
+     */
+    for (byte = 0; byte < nBytes; ++byte) {
+        /*
+         * Bring the next byte into the remainder.
+         */
+        remainder ^= (REFLECT_DATA(message[byte]) << (WIDTH - 8));
+
+        /*
+         * Perform modulo-2 division, a bit at a time.
+         */
+        for (bit = 8; bit > 0; --bit) {
+            /*
+             * Try to divide the current data bit.
+             */
+            if (remainder & TOPBIT) {
+                remainder = (remainder << 1) ^ POLYNOMIAL;
+            } else {
+                remainder = (remainder << 1);
+            }
+        }
+    }
+
+    /*
+     * The final remainder is the CRC result.
+     */
+    return (REFLECT_REMAINDER(remainder) ^ FINAL_XOR_VALUE);
+}   /* crcSlow() */