diff options
author | mtklein <mtklein@chromium.org> | 2016-02-11 06:30:03 -0800 |
---|---|---|
committer | Commit bot <commit-bot@chromium.org> | 2016-02-11 06:30:03 -0800 |
commit | fff055cc5f9ca5015678f4f13a4f842084bd62d5 (patch) | |
tree | f7e00567455fbd81ab5c1b401e4e80ed52a2095e /src/core/SkHalf.h | |
parent | cbefc5e4ca7fd7aaa5d2a3aa85b30f16148c3d2f (diff) |
SkHalfToFloat_01 / SkFloatToHalf_01
These are basically inlined, 4-at-a-time versions of our existing functions,
but cut down to avoid any work that's only necessary outside [0,1].
Both f16 and f32 denorms should work fine modulo the usual ARMv7 NEON denorm==zero caveat.
In exchange for a little speed, f32->f16 does not round properly.
Instead it truncates, so it's never off by more than 1 bit.
Support for finite values >1 or <0 is straightforward to add back.
>1 might already work as-is.
Getting close to _u16 performance:
micros bench
261.13 xferu64_bw_1_opaque_u16
1833.51 xferu64_bw_1_alpha_u16
2762.32 ? xferu64_aa_1_opaque_u16
3334.29 xferu64_aa_1_alpha_u16
249.78 xferu64_bw_1_opaque_f16
3383.18 xferu64_bw_1_alpha_f16
4214.72 xferu64_aa_1_opaque_f16
4701.19 xferu64_aa_1_alpha_f16
BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1685133005
Committed: https://skia.googlesource.com/skia/+/9ea11a4235b3e3521cc8bf914a27c2d0dc062db9
CQ_EXTRA_TRYBOTS=client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD-Trybot
Review URL: https://codereview.chromium.org/1685133005
Diffstat (limited to 'src/core/SkHalf.h')
-rw-r--r-- | src/core/SkHalf.h | 63 |
1 files changed, 63 insertions, 0 deletions
diff --git a/src/core/SkHalf.h b/src/core/SkHalf.h index 7e41c6ff0c..3937343b6c 100644 --- a/src/core/SkHalf.h +++ b/src/core/SkHalf.h @@ -8,6 +8,7 @@ #ifndef SkHalf_DEFINED #define SkHalf_DEFINED +#include "SkNx.h" #include "SkTypes.h" // 16-bit floating point value @@ -23,4 +24,66 @@ typedef uint16_t SkHalf; float SkHalfToFloat(SkHalf h); SkHalf SkFloatToHalf(float f); +// Convert between half and single precision floating point, but pull any dirty +// trick we can to make it faster as long as it's correct enough for values in [0,1]. +static inline Sk4f SkHalfToFloat_01(uint64_t); +static inline uint64_t SkFloatToHalf_01(const Sk4f&); + +// ~~~~~~~~~~~ impl ~~~~~~~~~~~~~~ // + +// Like the serial versions in SkHalf.cpp, these are based on +// https://fgiesen.wordpress.com/2012/03/28/half-to-float-done-quic/ + +// TODO: NEON versions +static inline Sk4f SkHalfToFloat_01(uint64_t hs) { +#if !defined(SKNX_NO_SIMD) && SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSE2 + // Load our 16-bit floats into the bottom 16 bits of each 32-bit lane, with zeroes on top. + __m128i h = _mm_unpacklo_epi16(_mm_loadl_epi64((const __m128i*)&hs), _mm_setzero_si128()); + + // Fork into two paths, depending on whether the 16-bit float is denormalized. + __m128 is_denorm = _mm_castsi128_ps(_mm_cmplt_epi32(h, _mm_set1_epi32(0x0400))); + + // TODO: figure out, explain + const __m128 half = _mm_set1_ps(0.5f); + __m128 denorm = _mm_sub_ps(_mm_or_ps(_mm_castsi128_ps(h), half), half); + + // If we're normalized, just shift ourselves so the exponent/mantissa dividing line + // is correct, then re-bias the exponent from 15 to 127. + __m128 norm = _mm_castsi128_ps(_mm_add_epi32(_mm_slli_epi32(h, 13), + _mm_set1_epi32((127-15) << 23))); + + return _mm_or_ps(_mm_and_ps (is_denorm, denorm), + _mm_andnot_ps(is_denorm, norm)); +#else + float fs[4]; + for (int i = 0; i < 4; i++) { + fs[i] = SkHalfToFloat(hs >> (i*16)); + } + return Sk4f::Load(fs); +#endif +} + +static inline uint64_t SkFloatToHalf_01(const Sk4f& fs) { +#if !defined(SKNX_NO_SIMD) && SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSE2 + // Scale our floats down by a tiny power of 2 to pull up our mantissa bits, + // then shift back down to 16-bit float layout. This doesn't round, so can be 1 bit small. + // TODO: understand better. Why this scale factor? + const __m128 scale = _mm_castsi128_ps(_mm_set1_epi32(15 << 23)); + __m128i h = _mm_srli_epi32(_mm_castps_si128(_mm_mul_ps(fs.fVec, scale)), 13); + + uint64_t r; + _mm_storel_epi64((__m128i*)&r, _mm_packs_epi32(h,h)); + return r; +#else + SkHalf hs[4]; + for (int i = 0; i < 4; i++) { + hs[i] = SkFloatToHalf(fs[i]); + } + return (uint64_t)hs[3] << 48 + | (uint64_t)hs[2] << 32 + | (uint64_t)hs[1] << 16 + | (uint64_t)hs[0] << 0; +#endif +} + #endif |