#include "crc32.h"

/* CRC-32/IEEE 802.3 查表实现（表在首次使用时生成，避免占用 Flash） */
static uint32_t crc32_table[256];
static uint8_t  crc32_table_ready = 0;

static void crc32_build_table(void)
{
    for (uint32_t i = 0; i < 256; i++)
    {
        uint32_t c = i;
        for (uint32_t k = 0; k < 8; k++)
        {
            c = (c & 1U) ? (0xEDB88320UL ^ (c >> 1)) : (c >> 1);
        }
        crc32_table[i] = c;
    }
    crc32_table_ready = 1;
}

uint32_t crc32_init(void)
{
    return 0xFFFFFFFFUL;
}

uint32_t crc32_update(uint32_t crc, const uint8_t *data, uint32_t len)
{
    if (!crc32_table_ready)
    {
        crc32_build_table();
    }
    while (len--)
    {
        crc = crc32_table[(crc ^ *data++) & 0xFFU] ^ (crc >> 8);
    }
    return crc;
}

uint32_t crc32_final(uint32_t crc)
{
    return crc ^ 0xFFFFFFFFUL;
}

uint32_t crc32_compute(const uint8_t *data, uint32_t len)
{
    return crc32_final(crc32_update(crc32_init(), data, len));
}