1 /* 2 * Copyright (C) 2021 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #include "chpp/crc.h" 18 19 #include <stddef.h> 20 #include <stdint.h> 21 22 uint32_t chppCrc32(uint32_t crc, const uint8_t *buf, size_t len) { 23 // This lookup table (LUT) consumes 16 * 4 = 64 bytes. Other implementations 24 // exist with a larger LUT, with a LUT calculated on the fly, or without using 25 // a LUT altogether. 26 static const uint32_t crc32LookupTable[] = { 27 0x00000000, 0x1DB71064, 0x3B6E20C8, 0x26D930AC, 0x76DC4190, 0x6B6B51F4, 28 0x4DB26158, 0x5005713C, 0xEDB88320, 0xF00F9344, 0xD6D6A3E8, 0xCB61B38C, 29 0x9B64C2B0, 0x86D3D2D4, 0xA00AE278, 0xBDBDF21C}; 30 31 crc = ~crc; 32 for (size_t i = 0; i < len; i++) { 33 crc = crc32LookupTable[(crc ^ buf[i]) & 0x0F] ^ (crc >> 4); 34 crc = crc32LookupTable[(crc ^ (buf[i] >> 4)) & 0x0F] ^ (crc >> 4); 35 } 36 crc = ~crc; 37 38 return crc; 39 } 40