c/c++语言开发共享CRC中的CRC32算法/实现没有查找表和公共许可证

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// ----------------------------- crc32b -------------------------------- /* This is the basic CRC-32 calculation with some optimization but no table lookup. The the byte reversal is avoided by shifting the crc reg right instead of left and by using a reversed 32-bit word to represent the polynomial. When compiled to Cyclops with GCC, this function executes in 8 + 72n instructions, where n is the number of bytes in the input message. It should be doable in 4 + 61n instructions. If the inner loop is strung out (approx. 5*8 = 40 instructions), it would take about 6 + 46n instructions. */ unsigned int crc32b(unsigned char *message) { int i, j; unsigned int byte, crc, mask; i = 0; crc = 0xFFFFFFFF; while (message[i] != 0) { byte = message[i]; // Get next byte. crc = crc ^ byte; for (j = 7; j >= 0; j--) { // Do eight times. mask = -(crc & 1); crc = (crc >> 1) ^ (0xEDB88320 & mask); } i = i + 1; } return ~crc; }