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| 1 /* |
| 2 * Copyright 2014 Google Inc. |
| 3 * |
| 4 * Use of this source code is governed by a BSD-style license that can be |
| 5 * found in the LICENSE file. |
| 6 */ |
| 7 |
| 8 #include "SkHalf.h" |
| 9 #include "SkFloatBits.h" |
| 10 |
| 11 uint16_t halfMantissa(SkHalf h) { |
| 12 return h & 0x03ff; |
| 13 } |
| 14 |
| 15 uint16_t halfExponent(SkHalf h) { |
| 16 return (h >> 10) & 0x001f; |
| 17 } |
| 18 |
| 19 uint16_t halfSign(SkHalf h) { |
| 20 return h >> 15; |
| 21 } |
| 22 |
| 23 union FloatUIntUnion { |
| 24 uint32_t fUInt; // this must come first for the initializations below to
work |
| 25 float fFloat; |
| 26 }; |
| 27 |
| 28 // based on Fabien Giesen's float_to_half_fast3() |
| 29 // see https://gist.github.com/rygorous/2156668 |
| 30 SkHalf SkFloatToHalf(float f) { |
| 31 static const uint32_t f32infty = { 255 << 23 }; |
| 32 static const uint32_t f16infty = { 31 << 23 }; |
| 33 static const FloatUIntUnion magic = { 15 << 23 }; |
| 34 static const uint32_t sign_mask = 0x80000000u; |
| 35 static const uint32_t round_mask = ~0xfffu; |
| 36 SkHalf o = 0; |
| 37 |
| 38 FloatUIntUnion floatUnion; |
| 39 floatUnion.fFloat = f; |
| 40 |
| 41 uint32_t sign = floatUnion.fUInt & sign_mask; |
| 42 floatUnion.fUInt ^= sign; |
| 43 |
| 44 // NOTE all the integer compares in this function can be safely |
| 45 // compiled into signed compares since all operands are below |
| 46 // 0x80000000. Important if you want fast straight SSE2 code |
| 47 // (since there's no unsigned PCMPGTD). |
| 48 |
| 49 // Inf or NaN (all exponent bits set) |
| 50 if (floatUnion.fUInt >= f32infty) |
| 51 // NaN->qNaN and Inf->Inf |
| 52 o = (floatUnion.fUInt > f32infty) ? 0x7e00 : 0x7c00; |
| 53 // (De)normalized number or zero |
| 54 else { |
| 55 floatUnion.fUInt &= round_mask; |
| 56 floatUnion.fFloat *= magic.fFloat; |
| 57 floatUnion.fUInt -= round_mask; |
| 58 // Clamp to signed infinity if overflowed |
| 59 if (floatUnion.fUInt > f16infty) { |
| 60 floatUnion.fUInt = f16infty; |
| 61 } |
| 62 |
| 63 o = floatUnion.fUInt >> 13; // Take the bits! |
| 64 } |
| 65 |
| 66 o |= sign >> 16; |
| 67 return o; |
| 68 } |
| 69 |
| 70 // based on Fabien Giesen's half_to_float_fast2() |
| 71 // see https://fgiesen.wordpress.com/2012/03/28/half-to-float-done-quic/ |
| 72 float SkHalfToFloat(SkHalf h) { |
| 73 static const FloatUIntUnion magic = { 126 << 23 }; |
| 74 FloatUIntUnion o; |
| 75 |
| 76 if (halfExponent(h) == 0) |
| 77 { |
| 78 // Zero / Denormal |
| 79 o.fUInt = magic.fUInt + halfMantissa(h); |
| 80 o.fFloat -= magic.fFloat; |
| 81 } |
| 82 else |
| 83 { |
| 84 // Set mantissa |
| 85 o.fUInt = halfMantissa(h) << 13; |
| 86 // Set exponent |
| 87 if (halfExponent(h) == 0x1f) |
| 88 // Inf/NaN |
| 89 o.fUInt |= (255 << 23); |
| 90 else |
| 91 o.fUInt |= ((127 - 15 + halfExponent(h)) << 23); |
| 92 } |
| 93 |
| 94 // Set sign |
| 95 o.fUInt |= (halfSign(h) << 31); |
| 96 return o.fFloat; |
| 97 } |
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