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 "include/private/SkFloatBits.h"
9#include "include/private/SkHalf.h"
10
11uint16_t halfMantissa(SkHalf h) {
12 return h & 0x03ff;
13}
14
15uint16_t halfExponent(SkHalf h) {
16 return (h >> 10) & 0x001f;
17}
18
19uint16_t halfSign(SkHalf h) {
20 return h >> 15;
21}
22
23union 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
30SkHalf 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/
72float 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}
98