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Diffstat (limited to 'engines/wintermute/utils/crc.cpp')
| -rw-r--r-- | engines/wintermute/utils/crc.cpp | 237 |
1 files changed, 237 insertions, 0 deletions
diff --git a/engines/wintermute/utils/crc.cpp b/engines/wintermute/utils/crc.cpp new file mode 100644 index 0000000000..e7ec45511b --- /dev/null +++ b/engines/wintermute/utils/crc.cpp @@ -0,0 +1,237 @@ +/********************************************************************** + * + * 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 "engines/wintermute/utils/crc.h" + +namespace Wintermute { + +/* + * 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 byteVal, crc remainder) { + unsigned char data; + data = (unsigned char)(REFLECT_DATA(byteVal) ^ (remainder >> (WIDTH - 8))); + remainder = crcTable[data] ^ (remainder << 8); + return remainder; +} + +crc crc_finalize(crc remainder) { + return (REFLECT_REMAINDER(remainder) ^ FINAL_XOR_VALUE); +} + +} // end of namespace Wintermute |