// crc32.c - CRC32 checksum implementation
#include "crc32.h"
#include <string.h>

static uint32_t crc32_table[256];
static int crc32_table_initialized = 0;

static void init_crc32_table(void) {
    if (crc32_table_initialized) return;
    
    for (uint32_t i = 0; i < 256; i++) {
        uint32_t crc = i;
        for (int j = 0; j < 8; j++) {
            if (crc & 1) {
                crc = (crc >> 1) ^ 0xEDB88320;
            } else {
                crc >>= 1;
            }
        }
        crc32_table[i] = crc;
    }
    
    crc32_table_initialized = 1;
}

void crc32_init(void) {
    init_crc32_table();
}

uint32_t crc32_calc(const uint8_t *data, size_t len) {
    if (!crc32_table_initialized) {
        init_crc32_table();
    }
    
    if (!data || len == 0) return 0xFFFFFFFF;
    
    uint32_t crc = 0xFFFFFFFF;
    for (size_t i = 0; i < len; i++) {
        uint8_t byte = data[i];
        uint32_t table_index = (crc ^ byte) & 0xFF;
        crc = (crc >> 8) ^ crc32_table[table_index];
    }
    
    return ~crc;
}

uint32_t crc32_calc_ex(const uint8_t *data, size_t len, uint32_t initial_crc) {
    if (!crc32_table_initialized) {
        init_crc32_table();
    }
    
    if (!data || len == 0) return initial_crc;
    
    uint32_t crc = initial_crc;
    for (size_t i = 0; i < len; i++) {
        uint8_t byte = data[i];
        uint32_t table_index = (crc ^ byte) & 0xFF;
        crc = (crc >> 8) ^ crc32_table[table_index];
    }
    
    return crc;
}

uint32_t crc32_update(uint32_t crc, const uint8_t *data, size_t len) {
    return crc32_calc_ex(data, len, crc);
}