Justin Pettit
41 lines
890 B
C
41 lines
890 B
C
/*
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* Distributed under the terms of the GNU GPL version 2.
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* Copyright (c) 2007, 2008 The Board of Trustees of The Leland
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* Stanford Junior University
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*/
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#include "crc32.h"
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void crc32_init(struct crc32 *crc, unsigned int polynomial)
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{
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int i;
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for (i = 0; i < CRC32_TABLE_SIZE; ++i) {
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unsigned int reg = i << 24;
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int j;
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for (j = 0; j < CRC32_TABLE_BITS; j++) {
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int topBit = (reg & 0x80000000) != 0;
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reg <<= 1;
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if (topBit)
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reg ^= polynomial;
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}
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crc->table[i] = reg;
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}
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}
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unsigned int crc32_calculate(const struct crc32 *crc,
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const void *data_, size_t n_bytes)
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{
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// FIXME: this can be optimized by unrolling, see linux-2.6/lib/crc32.c.
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const uint8_t *data = data_;
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unsigned int result = 0;
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size_t i;
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for (i = 0; i < n_bytes; i++) {
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unsigned int top = result >> 24;
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top ^= data[i];
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result = (result << 8) ^ crc->table[top];
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}
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return result;
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}
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