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Diffstat (limited to 'engines/wintermute/crc.cpp')
| -rw-r--r-- | engines/wintermute/crc.cpp | 234 |
1 files changed, 234 insertions, 0 deletions
diff --git a/engines/wintermute/crc.cpp b/engines/wintermute/crc.cpp new file mode 100644 index 0000000000..503f8242fa --- /dev/null +++ b/engines/wintermute/crc.cpp @@ -0,0 +1,234 @@ +/**********************************************************************
+ *
+ * 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.
+ **********************************************************************/
+
+#include "crc.h"
+
+
+/*
+ * 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.
+ *
+ *********************************************************************/
+crc
+crcSlow(unsigned char const message[], int nBytes) {
+ crc remainder = INITIAL_REMAINDER;
+ int byte;
+ unsigned char bit;
+
+
+ /*
+ * 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() */
+
+
+crc crcTable[256];
+
+
+/*********************************************************************
+ *
+ * Function: crcInit()
+ *
+ * Description: Populate the partial CRC lookup table.
+ *
+ * Notes: This function must be rerun any time the CRC standard
+ * is changed. If desired, it can be run "offline" and
+ * the table results stored in an embedded system's ROM.
+ *
+ * Returns: None defined.
+ *
+ *********************************************************************/
+void
+crcInit(void) {
+ crc remainder;
+ int dividend;
+ unsigned char bit;
+
+
+ /*
+ * Compute the remainder of each possible dividend.
+ */
+ for (dividend = 0; dividend < 256; ++dividend) {
+ /*
+ * Start with the dividend followed by zeros.
+ */
+ remainder = dividend << (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);
+ }
+ }
+
+ /*
+ * Store the result into the table.
+ */
+ crcTable[dividend] = remainder;
+ }
+
+} /* crcInit() */
+
+
+/*********************************************************************
+ *
+ * Function: crcFast()
+ *
+ * Description: Compute the CRC of a given message.
+ *
+ * Notes: crcInit() must be called first.
+ *
+ * Returns: The CRC of the message.
+ *
+ *********************************************************************/
+crc
+crcFast(unsigned char const message[], int nBytes) {
+ crc remainder = INITIAL_REMAINDER;
+ unsigned char data;
+ int byte;
+
+
+ /*
+ * Divide the message by the polynomial, a byte at a time.
+ */
+ for (byte = 0; byte < nBytes; ++byte) {
+ data = (unsigned char)(REFLECT_DATA(message[byte]) ^ (remainder >> (WIDTH - 8)));
+ remainder = crcTable[data] ^ (remainder << 8);
+ }
+
+ /*
+ * The final remainder is the CRC.
+ */
+ return (REFLECT_REMAINDER(remainder) ^ FINAL_XOR_VALUE);
+
+} /* crcFast() */
+
+
+
+crc crc_initialize(void) {
+ crcInit();
+ return INITIAL_REMAINDER;
+}
+
+crc crc_process_byte(unsigned char byte, crc remainder) {
+ unsigned char data;
+ data = (unsigned char)(REFLECT_DATA(byte ) ^ (remainder >> (WIDTH - 8)));
+ remainder = crcTable[data] ^ (remainder << 8);
+ return remainder;
+}
+
+crc crc_finalize(crc remainder) {
+ return (REFLECT_REMAINDER(remainder) ^ FINAL_XOR_VALUE);
+}
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