jvanverth | 9367992 | 2014-11-26 13:15:59 -0800 | [diff] [blame] | 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; |
halcanary | 9d524f2 | 2016-03-29 09:03:52 -0700 | [diff] [blame] | 37 | |
jvanverth | 9367992 | 2014-11-26 13:15:59 -0800 | [diff] [blame] | 38 | FloatUIntUnion floatUnion; |
| 39 | floatUnion.fFloat = f; |
halcanary | 9d524f2 | 2016-03-29 09:03:52 -0700 | [diff] [blame] | 40 | |
jvanverth | 9367992 | 2014-11-26 13:15:59 -0800 | [diff] [blame] | 41 | uint32_t sign = floatUnion.fUInt & sign_mask; |
| 42 | floatUnion.fUInt ^= sign; |
halcanary | 9d524f2 | 2016-03-29 09:03:52 -0700 | [diff] [blame] | 43 | |
jvanverth | 9367992 | 2014-11-26 13:15:59 -0800 | [diff] [blame] | 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). |
halcanary | 9d524f2 | 2016-03-29 09:03:52 -0700 | [diff] [blame] | 48 | |
jvanverth | 9367992 | 2014-11-26 13:15:59 -0800 | [diff] [blame] | 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 | } |
halcanary | 9d524f2 | 2016-03-29 09:03:52 -0700 | [diff] [blame] | 62 | |
jvanverth | 9367992 | 2014-11-26 13:15:59 -0800 | [diff] [blame] | 63 | o = floatUnion.fUInt >> 13; // Take the bits! |
| 64 | } |
halcanary | 9d524f2 | 2016-03-29 09:03:52 -0700 | [diff] [blame] | 65 | |
jvanverth | 9367992 | 2014-11-26 13:15:59 -0800 | [diff] [blame] | 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; |
halcanary | 9d524f2 | 2016-03-29 09:03:52 -0700 | [diff] [blame] | 75 | |
jvanverth | 9367992 | 2014-11-26 13:15:59 -0800 | [diff] [blame] | 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 | } |
halcanary | 9d524f2 | 2016-03-29 09:03:52 -0700 | [diff] [blame] | 93 | |
jvanverth | 9367992 | 2014-11-26 13:15:59 -0800 | [diff] [blame] | 94 | // Set sign |
| 95 | o.fUInt |= (halfSign(h) << 31); |
| 96 | return o.fFloat; |
| 97 | } |