85543f3d19
- Update Makefile:
- Change test binary name to `libicmp.test`.
- Add `-Wpedantic` and `-Wconversion` to global CFLAGS for stricter
warnings.
- Add dedicated `TEST_CFLAGS`.
- Ensure test build uses `TEST_CFLAGS`.
- Refactor code for better correctness.
BREAKING CHANGE: Test binary is now named `libicmp.test` instead of
`test.out` and stricter compiler flags may trigger new warnings or
errors in code outside this patch.
64 lines
1.4 KiB
C
64 lines
1.4 KiB
C
#include <stdint.h>
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#include <stddef.h>
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/* Forward Declarations */
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static inline uint16_t read_be16(const uint8_t *ptr);
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static uint32_t sum_words(const uint8_t *data, size_t len);
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static inline uint16_t fold_carries(uint32_t sum);
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/* -------------------- */
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/* RFC 1071: Compute ICMP checksum (16-bit one's complement sum) */
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uint16_t
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icmp_checksum(const void *data, size_t len)
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{
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uint32_t sum;
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sum = sum_words(data, len);
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sum = fold_carries(sum);
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return (uint16_t)~sum;
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}
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/* Sum all 16-bit words */
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static uint32_t
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sum_words(const uint8_t *data, size_t len)
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{
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const uint8_t *ptr = data;
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uint32_t sum = 0;
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size_t words = len >> 1;
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/* Duff's device: unroll loop by 4 */
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if (words > 0)
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{
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size_t n = (words + 3) >> 2;
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switch (words & 3) {
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case 0: do { sum += read_be16(ptr); ptr += 2;
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case 3: sum += read_be16(ptr); ptr += 2;
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case 2: sum += read_be16(ptr); ptr += 2;
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case 1: sum += read_be16(ptr); ptr += 2;
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} while (--n > 0);
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}
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}
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/* Handle odd byte if present */
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if (len & 1)
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sum += (uint32_t)(*ptr << 8);
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return sum;
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}
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/* Fold 32-bit sum to 16 bits by adding carry bits back */
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static inline uint16_t
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fold_carries(uint32_t sum)
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{
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while (sum >> 16)
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sum = (sum & 0xFFFF) + (sum >> 16);
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return (uint16_t)sum;
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}
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/* Read 16-bit word in network byte order (big-endian) */
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static inline uint16_t
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read_be16(const uint8_t *ptr)
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{
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return (uint16_t)((*ptr << 8) | ptr[1]);
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}
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