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fix: use arithmetic HexEncode instead of lookups #12

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Merged
lemire merged 5 commits into from
Feb 11, 2026
+7 −3
Merged

fix: use arithmetic HexEncode instead of lookups #12

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e72494a
src: use arithmetic HexEncode instead of lookups
ChALkeR Feb 2, 2026
8cb0b72
fixup!: lint
ChALkeR Feb 2, 2026
e65cb9e
fixup!: constexpr
ChALkeR Feb 2, 2026
61f4ecb
fixup!: more clear code
ChALkeR Feb 2, 2026
f221227
fixup!: lint
ChALkeR Feb 4, 2026
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7 changes: 4 additions & 3 deletions src/nbytes.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -157,17 +157,18 @@ const int8_t unhex_table[256] = {
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1};

inline char nibble(uint8_t x) { return x + '0' + ((x > 9) * 39); }
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@anonrig anonrig Feb 2, 2026

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Can you add a comment to this function and explain what it does?

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@lemire lemire Feb 2, 2026

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I think that if you express it as I did above, it does not require an explanation anymore.

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@ChALkeR ChALkeR Feb 5, 2026

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@anonrig is this still needed with the rewritten function?


size_t HexEncode(const char *src, size_t slen, char *dst, size_t dlen) {
// We know how much we'll write, just make sure that there's space.
NBYTES_ASSERT_TRUE(dlen >= MultiplyWithOverflowCheck<size_t>(slen, 2u) &&
"not enough space provided for hex encode");

dlen = slen * 2;
for (size_t i = 0, k = 0; k < dlen; i += 1, k += 2) {
static const char hex[] = "0123456789abcdef";
uint8_t val = static_cast<uint8_t>(src[i]);
dst[k + 0] = hex[val >> 4];
dst[k + 1] = hex[val & 15];
dst[k + 0] = nibble(val >> 4);
dst[k + 1] = nibble(val & 15);
}

return dlen;
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