68 lines
1.2 KiB
C
68 lines
1.2 KiB
C
#include <stdio.h>
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unsigned long _crcTable[256];
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int _crcTableInitialized = 0;
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#define CRC32_POLYNOMIAL 0xEDB88320L
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void CRCTable_Init() {
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int i;
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int j;
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unsigned long crc;
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if (_crcTableInitialized) {
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return;
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}
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_crcTableInitialized = 1;
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for (i = 0; i < 256; i++) {
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crc = i;
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for (j = 8; j > 0; j--) {
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if (crc & 1)
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crc = (crc >> 1) ^ CRC32_POLYNOMIAL;
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else
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crc >>= 1;
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}
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_crcTable[i] = crc;
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}
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}
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unsigned long CRC_BufferInternal(unsigned char *buffer, int len,
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unsigned long crc) {
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unsigned char *p;
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// Calcular CRC del buffer
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p = (unsigned char*) buffer;
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while (len-- != 0) {
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unsigned long termA = (crc >> 8) & 0x00FFFFFFL;
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unsigned long termB = _crcTable[((int) crc ^ *p++) & 0xff];
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crc = termA ^ termB;
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}
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return (crc);
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}
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unsigned long CRC_Buffer(unsigned char *buffer, int len, unsigned long crc) {
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CRCTable_Init();
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return (CRC_BufferInternal(buffer, len, crc));
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}
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unsigned long CRC_File(FILE *file) {
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unsigned long crc;
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unsigned char buffer[512];
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CRCTable_Init();
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crc = 0xFFFFFFFFL;
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for (;;) {
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// Llenar el buffer
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int count = fread(buffer, 1, 512, file);
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if (count == 0)
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break;
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// Calcular CRC del buffer
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crc = CRC_BufferInternal(buffer, count, crc);
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}
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return (crc ^= 0xFFFFFFFFL);
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}
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