45 lines
1.0 KiB
Objective-C
45 lines
1.0 KiB
Objective-C
#import "Crc32.h"
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#define DEFAULT_POLYNOMIAL 0xEDB88320L
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#define DEFAULT_SEED 0xFFFFFFFFL
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void generateCRC32Table(uint32_t *pTable, uint32_t poly);
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@implementation NSData (CRC)
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void generateCRC32Table(uint32_t *pTable, uint32_t poly) {
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for (uint32_t i = 0; i <= 255; i++) {
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uint32_t crc = i;
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for (uint32_t j = 8; j > 0; j--) {
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if ((crc & 1) == 1)
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crc = (crc >> 1) ^ poly;
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else
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crc >>= 1;
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}
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pTable[i] = crc;
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}
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}
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- (uint32_t)crc32 {
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return [self crc32WithSeed:DEFAULT_SEED usingPolynomial:DEFAULT_POLYNOMIAL];
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}
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- (uint32_t)crc32WithSeed:(uint32_t)seed usingPolynomial:(uint32_t)poly {
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uint32_t *pTable = malloc(sizeof(uint32_t) * 256);
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generateCRC32Table(pTable, poly);
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uint32_t crc = seed;
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uint8_t *pBytes = (uint8_t *)[self bytes];
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NSUInteger length = self.length;
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while (length--) {
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crc = (crc >> 8) ^ pTable[(crc & 0xFF) ^ *pBytes++];
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}
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free(pTable);
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return crc ^ 0xFFFFFFFFL;
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}
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@end
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