crc.cc

来自「M5,一个功能强大的多处理器系统模拟器.很多针对处理器架构,性能的研究都使用它作」· CC 代码 · 共 115 行

/*
 * Copyright (c) 1988, 1992, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <string>

#include "sim/host.hh"
#include "base/crc.hh"

#define ETHER_CRC_POLY_LE 0xedb88320
#define ETHER_CRC_POLY_BE 0x04c11db6

#if 0
/*
 * This is for reference.  We have a table-driven version
 * of the little-endian crc32 generator, which is faster
 * than the double-loop.
 */
uint32_t
crc32le(const uint8_t *buf, size_t len)
{
    uint32_t c, crc, carry;
    size_t i, j;

    crc = 0xffffffffU;      /* initial value */

    for (i = 0; i < len; i++) {
        c = buf[i];
        for (j = 0; j < 8; j++) {
            carry = ((crc & 0x01) ? 1 : 0) ^ (c & 0x01);
            crc >>= 1;
            c >>= 1;
            if (carry)
                crc = (crc ^ ETHER_CRC_POLY_LE);
        }
    }

    return (crc);
}
#else
uint32_t
crc32le(const uint8_t *buf, size_t len)
{
    static const uint32_t crctab[] = {
        0x00000000, 0x1db71064, 0x3b6e20c8, 0x26d930ac,
        0x76dc4190, 0x6b6b51f4, 0x4db26158, 0x5005713c,
        0xedb88320, 0xf00f9344, 0xd6d6a3e8, 0xcb61b38c,
        0x9b64c2b0, 0x86d3d2d4, 0xa00ae278, 0xbdbdf21c
    };
    uint32_t crc;
    int i;

    crc = 0xffffffffU;      /* initial value */

    for (i = 0; i < len; i++) {
        crc ^= buf[i];
        crc = (crc >> 4) ^ crctab[crc & 0xf];
        crc = (crc >> 4) ^ crctab[crc & 0xf];
    }

    return (crc);
}
#endif

uint32_t
crc32be(const uint8_t *buf, size_t len)
{
    uint32_t c, crc, carry;
    size_t i, j;

    crc = 0xffffffffU;      /* initial value */

    for (i = 0; i < len; i++) {
        c = buf[i];
        for (j = 0; j < 8; j++) {
            carry = ((crc & 0x80000000U) ? 1 : 0) ^ (c & 0x01);
            crc <<= 1;
            c >>= 1;
            if (carry)
                crc = (crc ^ ETHER_CRC_POLY_BE) | carry;
        }
    }

    return (crc);
}