diff options
Diffstat (limited to 'src/opts/SkNx_sse.h')
| -rw-r--r-- | src/opts/SkNx_sse.h | 13 |
1 files changed, 6 insertions, 7 deletions
diff --git a/src/opts/SkNx_sse.h b/src/opts/SkNx_sse.h index def7ba1719..7d00ddf9ba 100644 --- a/src/opts/SkNx_sse.h +++ b/src/opts/SkNx_sse.h @@ -14,14 +14,13 @@ #define SKNX_IS_FAST // SSE 4.1 has _mm_floor_ps to floor 4 floats. We emulate it: -// - round by adding (1<<23) with our sign, then subtracting it; -// - if that rounded value is bigger than our input, subtract 1. +// - roundtrip through integers via truncation +// - subtract 1 if that's too big (possible for negative values). +// This restricts the domain of our inputs to a maximum somehwere around 2^31. Seems plenty big. static inline __m128 sse2_mm_floor_ps(__m128 v) { - __m128 sign = _mm_and_ps(v, _mm_set1_ps(-0.0f)); - __m128 bias = _mm_or_ps(sign, _mm_set1_ps(1<<23)); - __m128 rounded = _mm_sub_ps(_mm_add_ps(v, bias), bias); - __m128 too_big = _mm_cmpgt_ps(rounded, v); - return _mm_sub_ps(rounded, _mm_and_ps(too_big, _mm_set1_ps(1.0f))); + __m128 roundtrip = _mm_cvtepi32_ps(_mm_cvttps_epi32(v)); + __m128 too_big = _mm_cmpgt_ps(roundtrip, v); + return _mm_sub_ps(roundtrip, _mm_and_ps(too_big, _mm_set1_ps(1.0f))); } template <> |