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Makes zigzag encoding and decoding save wrt. undefined behavior, see #28 #35

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Makes zigzag encoding and decoding save wrt. undefined behavior, see #28 #35

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4 changes: 2 additions & 2 deletions src/streamvbyte_zigzag.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@

static inline
uint32_t _zigzag_encode_32 (int32_t val) {
return (val + val) ^ (val >> 31);
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The signed val + val here is the issue wrt. overflow causing undefined behavior

return ((uint32_t)val << (uint32_t)1) ^ (uint32_t)(-(int32_t)((uint32_t)val >> (uint32_t)31));
}

void zigzag_encode(const int32_t * in, uint32_t * out, size_t N) {
Expand All @@ -19,7 +19,7 @@ void zigzag_delta_encode(const int32_t * in, uint32_t * out, size_t N, int32_t p

static inline
int32_t _zigzag_decode_32 (uint32_t val) {
return (val >> 1) ^ -(val & 1);
return (int32_t)((val >> (uint32_t)1) ^ (uint32_t)(-(int32_t)(val & (uint32_t)1)));
}


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30 changes: 30 additions & 0 deletions tests/unit.c
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Expand Up @@ -47,6 +47,36 @@ int zigzagtests() {
return isok;
}

// Fixtures from https://developers.google.com/protocol-buffers/docs/encoding#signed_integers
int zigzagfixturestests() {
const int32_t original[] = {0, -1, 1, -2, 2147483647, -2147483648};
const uint32_t encoded[] = {0, 1, 2, 3, 4294967294, 4294967295};

uint32_t out[] = {0xaaaaaaaa, 0xaaaaaaaa, 0xaaaaaaaa, 0xaaaaaaaa, 0xaaaaaaaa, 0xaaaaaaaa};

zigzag_encode(original, out, 6);

for (size_t i = 0; i < 6; ++i) {
if (encoded[i] != out[i]) {
printf("[zigzag_encode] %ju != %ju\n", (uintmax_t)encoded[i], (uintmax_t)out[i]);
return -1;
}
}

int32_t roundtrip[] = {0x55555555, 0x55555555, 0x55555555, 0x55555555, 0x55555555, 0x55555555};

zigzag_decode((const uint32_t *)out, roundtrip, 6);

for (size_t i = 0; i < 6; ++i) {
if (original[i] != roundtrip[i]) {
printf("[zigzag_decode] %jd != %jd\n", (intmax_t)original[i], (intmax_t)roundtrip[i]);
return -1;
}
}

return 0;
}

// return -1 in case of failure
int basictests() {
int N = 4096;
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