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
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