esp-idf/components/nvs_flash/test/crc.cpp

// Copyright 2015-2016 Espressif Systems (Shanghai) PTE LTD
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at

//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include <stdint.h>
#include <stdbool.h>

extern "C" unsigned long crc32_le(unsigned long crc_in, unsigned char const* data, unsigned int length)
{
    uint32_t i;
    bool bit;
    uint8_t c;
    uint32_t crc = (uint32_t) crc_in;

    while (length--) {
        c = *data++;
        for (i = 0x80; i > 0; i >>= 1) {
            bit = crc & 0x80000000;
            if (c & i) {
                bit = !bit;
            }
            crc <<= 1;
            if (bit) {
                crc ^= 0x04c11db7;
            }
        }
    }
    return crc;
}