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/*
* Copyright 2014 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include "SkHalf.h"
#include "SkFloatBits.h"
uint16_t halfMantissa(SkHalf h) {
return h & 0x03ff;
}
uint16_t halfExponent(SkHalf h) {
return (h >> 10) & 0x001f;
}
uint16_t halfSign(SkHalf h) {
return h >> 15;
}
union FloatUIntUnion {
uint32_t fUInt; // this must come first for the initializations below to work
float fFloat;
};
// based on Fabien Giesen's float_to_half_fast3()
// see https://gist.github.com/rygorous/2156668
SkHalf SkFloatToHalf(float f) {
static const uint32_t f32infty = { 255 << 23 };
static const uint32_t f16infty = { 31 << 23 };
static const FloatUIntUnion magic = { 15 << 23 };
static const uint32_t sign_mask = 0x80000000u;
static const uint32_t round_mask = ~0xfffu;
SkHalf o = 0;
FloatUIntUnion floatUnion;
floatUnion.fFloat = f;
uint32_t sign = floatUnion.fUInt & sign_mask;
floatUnion.fUInt ^= sign;
// NOTE all the integer compares in this function can be safely
// compiled into signed compares since all operands are below
// 0x80000000. Important if you want fast straight SSE2 code
// (since there's no unsigned PCMPGTD).
// Inf or NaN (all exponent bits set)
if (floatUnion.fUInt >= f32infty)
// NaN->qNaN and Inf->Inf
o = (floatUnion.fUInt > f32infty) ? 0x7e00 : 0x7c00;
// (De)normalized number or zero
else {
floatUnion.fUInt &= round_mask;
floatUnion.fFloat *= magic.fFloat;
floatUnion.fUInt -= round_mask;
// Clamp to signed infinity if overflowed
if (floatUnion.fUInt > f16infty) {
floatUnion.fUInt = f16infty;
}
o = floatUnion.fUInt >> 13; // Take the bits!
}
o |= sign >> 16;
return o;
}
// based on Fabien Giesen's half_to_float_fast2()
// see https://fgiesen.wordpress.com/2012/03/28/half-to-float-done-quic/
float SkHalfToFloat(SkHalf h) {
static const FloatUIntUnion magic = { 126 << 23 };
FloatUIntUnion o;
if (halfExponent(h) == 0)
{
// Zero / Denormal
o.fUInt = magic.fUInt + halfMantissa(h);
o.fFloat -= magic.fFloat;
}
else
{
// Set mantissa
o.fUInt = halfMantissa(h) << 13;
// Set exponent
if (halfExponent(h) == 0x1f)
// Inf/NaN
o.fUInt |= (255 << 23);
else
o.fUInt |= ((127 - 15 + halfExponent(h)) << 23);
}
// Set sign
o.fUInt |= (halfSign(h) << 31);
return o.fFloat;
}
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