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51 lines
1.6 KiB
C
51 lines
1.6 KiB
C
/*
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* Copyright 2024 Google LLC
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "util/crc32.h"
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#include <stdint.h>
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#include <string.h>
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// Nybble-wide table driven CRC-32 algorithm
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//
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// A compromise between speed and size, this algorithm uses a lookup table to
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// calculate the CRC four bits at a time with a size cost of only 64 bytes. By
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// contrast, a byte-wide algorithm requires a lookup table sixteen times larger!
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//
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// The lookup table is generated by the crc32_lut.py
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static const uint32_t s_lookup_table[] = {
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0x00000000, 0x1db71064, 0x3b6e20c8, 0x26d930ac,
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0x76dc4190, 0x6b6b51f4, 0x4db26158, 0x5005713c,
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0xedb88320, 0xf00f9344, 0xd6d6a3e8, 0xcb61b38c,
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0x9b64c2b0, 0x86d3d2d4, 0xa00ae278, 0xbdbdf21c,
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};
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uint32_t crc32(uint32_t crc, const void * restrict data, size_t length) {
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if (data == 0) {
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return 0;
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}
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const uint8_t * restrict bytes = data;
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crc ^= 0xffffffff;
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while (length--) {
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crc = (crc >> 4) ^ s_lookup_table[(crc ^ *bytes) & 0xf];
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crc = (crc >> 4) ^ s_lookup_table[(crc ^ (*bytes >> 4)) & 0xf];
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bytes++;
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}
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crc ^= 0xffffffff;
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return crc;
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}
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