km
b1c3ec3af4
- Protocol definition with 6-byte header (chunk_idx: 2B, payload: N B, crc32: 4B) - Node.js server with chunk-based HTTP delivery - C client library with resumable download support - CRC32 implementation (IEEE 802.3) - Test suites for both server and CRC32 - 1024B default chunk size (0.59% overhead)
78 lines
1.8 KiB
C
78 lines
1.8 KiB
C
/**
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* @file crc32.c
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* @brief CRC32 Implementation (IEEE 802.3)
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*/
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#include <stdint.h>
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#include <stddef.h>
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#include <stdbool.h>
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/* IEEE 802.3 CRC32 polynomial (reversed) */
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#define CRC32_POLY 0xEDB88320UL
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/* CRC32 lookup table (256 entries) */
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static uint32_t crc32_table[256];
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static bool crc32_table_init = false;
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/**
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* Initialize CRC32 lookup table
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*/
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static void crc32_init_table(void) {
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if (crc32_table_init) return;
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for (uint32_t i = 0; i < 256; i++) {
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uint32_t crc = i;
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for (int j = 0; j < 8; j++) {
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if (crc & 1) {
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crc = (crc >> 1) ^ CRC32_POLY;
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} else {
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crc >>= 1;
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}
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}
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crc32_table[i] = crc;
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}
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crc32_table_init = true;
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}
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/**
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* Calculate CRC32 (IEEE 802.3 polynomial)
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*
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* @param data Input data
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* @param len Input length
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* @return CRC32 value
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*/
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uint32_t chunk_crc32(const uint8_t *data, size_t len) {
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crc32_init_table();
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uint32_t crc = 0xFFFFFFFFUL; /* Initial value */
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for (size_t i = 0; i < len; i++) {
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uint8_t index = (crc ^ data[i]) & 0xFF;
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crc = (crc >> 8) ^ crc32_table[index];
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}
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return crc ^ 0xFFFFFFFFUL; /* Final XOR */
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}
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/**
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* Update CRC32 with additional data
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*
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* @param crc Previous CRC value (already XORed with 0xFFFFFFFF)
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* @param data New data
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* @param len Data length
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* @return Updated CRC value
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*/
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uint32_t chunk_crc32_update(uint32_t crc, const uint8_t *data, size_t len) {
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crc32_init_table();
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/* Undo final XOR from previous calculation */
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crc ^= 0xFFFFFFFFUL;
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for (size_t i = 0; i < len; i++) {
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uint8_t index = (crc ^ data[i]) & 0xFF;
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crc = (crc >> 8) ^ crc32_table[index];
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}
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return crc ^ 0xFFFFFFFFUL; /* Final XOR */
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}
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