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Fix SSE2 variant of TextColor::GetColor (#10867)

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Shortly before adding the SSE2 variant I "improved" it by using
`_mm_packs_epi32`, but failed to test it again afterwards.

## PR Checklist
* [x] Closes #10866
* [x] I work here

## Validation Steps Performed

* `printf "\e[mNORMAL \e[1mBOLD\n"` results in correct bold white glyphs ✔️
This commit is contained in:
Leonard Hecker 2021-08-04 17:57:20 +02:00 committed by GitHub
parent 8ab3422b57
commit aea725f885
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1 changed files with 6 additions and 3 deletions
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9
src/buffer/out/TextColor.cpp
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@ -192,21 +192,24 @@ COLORREF TextColor::GetColor(const std::array<COLORREF, 256>& colorTable, const
unsigned long index;
return _BitScanForward(&index, mask) ? til::at(colorTable, static_cast<size_t>(index) + 8) : defaultColor; // 5.
#elif _M_AMD64
// If you look closely this SSE2 algorithm is the exact same as the AVX one.
// If you look closely this SSE2 algorithm is the same as the AVX one.
// The two differences are that we need to:
// * do everything twice, because SSE is limited to 128 bits and not 256.
// * use _mm_packs_epi32 to merge two 128 bits vectors into one in step 3.5.
// _mm_packs_epi32 takes two SSE registers and truncates all 8 DWORDs into 8 WORDs,
// the latter of which fits into a single register (which is then used in the identical step 4).
// * since the result are now 8 WORDs, we need to use _mm_movemask_epi8 (there's no 16-bit variant),
// which unlike AVX's step 4 results in in something like 0b0000110000000000.
// --> the index returned by _BitScanForward must be divided by 2.
const auto haystack1 = _mm_loadu_si128(reinterpret_cast<const __m128i*>(colorTable.data() + 0));
const auto haystack2 = _mm_loadu_si128(reinterpret_cast<const __m128i*>(colorTable.data() + 4));
const auto needle = _mm_set1_epi32(__builtin_bit_cast(int, defaultColor));
const auto result1 = _mm_cmpeq_epi32(haystack1, needle);
const auto result2 = _mm_cmpeq_epi32(haystack2, needle);
const auto result = _mm_packs_epi32(result1, result2); // 3.5
const auto mask = _mm_movemask_ps(_mm_castsi128_ps(result));
const auto mask = _mm_movemask_epi8(result);
unsigned long index;
return _BitScanForward(&index, mask) ? til::at(colorTable, static_cast<size_t>(index) + 8) : defaultColor;
return _BitScanForward(&index, mask) ? til::at(colorTable, static_cast<size_t>(index / 2) + 8) : defaultColor;
#else
for (size_t i = 0; i < 8; i++)
{