Is there any way to make these two functions run faster?
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// linear2sRGB is a sRGB encoder
func linear2sRGB(v float64) float64 {
if v <= 0.0031308 {
v *= 12.92
} else {
v = 1.055*math.Pow(v, 1/2.4) - 0.055
}
return v
}
// sRGB2linear is a sRGB decoder
func sRGB2linear(v float64) float64 {
if v <= 0.04045 {
v /= 12.92
} else {
v = math.Pow((v+0.055)/1.055, 2.4)
}
return v
}
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Here’s a straightforward optimization: lookup table + linear interpolation:
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// Linear2sRGB converts linear inputs to sRGB space.
func Linear2sRGB(v float64) float64 {
i := v * lutSize
ifloor := int(i) & (lutSize - 1)
v0 := lin2sRGBLUT[ifloor]
v1 := lin2sRGBLUT[ifloor+1]
i -= float64(ifloor)
return v0*(1.0-i) + v1*i
}
func linear2sRGB(v float64) float64 {
if v <= 0.0031308 {
v *= 12.92
} else {
v = 1.055*math.Pow(v, 1/2.4) - 0.055
}
return v
}
const lutSize = 1024 // keep a power of 2
var lin2sRGBLUT [lutSize + 1]float64
func init() {
for i := range lin2sRGBLUT[:lutSize] {
lin2sRGBLUT[i] = linear2sRGB(float64(i) / lutSize)
}
lin2sRGBLUT[lutSize] = lin2sRGBLUT[lutSize-1]
}
func BenchmarkLinear2sRGB(b *testing.B) {
for i := 0; i < b.N; i++ {
for j := 0.0; j <= 1.0; j += 0.01 {
convert.Linear2sRGB(j)
}
}
}
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The benchmark shows approximately 98% runtime performance improvement after optimization.
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name old time/op new time/op delta
Linear2sRGB-6 6.38µs ± 0% 0.14µs ± 0% -97.87% (p=0.000 n=10+8)
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有什么办法能够让这两个函数跑得更快吗？
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// linear2sRGB is a sRGB encoder
func linear2sRGB(v float64) float64 {
if v <= 0.0031308 {
v *= 12.92
} else {
v = 1.055*math.Pow(v, 1/2.4) - 0.055
}
return v
}
// sRGB2linear is a sRGB decoder
func sRGB2linear(v float64) float64 {
if v <= 0.04045 {
v /= 12.92
} else {
v = math.Pow((v+0.055)/1.055, 2.4)
}
return v
}
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这里介绍一个很平凡的优化方案: lookup table + 线性插值:
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// Linear2sRGB converts linear inputs to sRGB space.
func Linear2sRGB(v float64) float64 {
i := v * lutSize
ifloor := int(i) & (lutSize - 1)
v0 := lin2sRGBLUT[ifloor]
v1 := lin2sRGBLUT[ifloor+1]
i -= float64(ifloor)
return v0*(1.0-i) + v1*i
}
func linear2sRGB(v float64) float64 {
if v <= 0.0031308 {
v *= 12.92
} else {
v = 1.055*math.Pow(v, 1/2.4) - 0.055
}
return v
}
const lutSize = 1024 // keep a power of 2
var lin2sRGBLUT [lutSize + 1]float64
func init() {
for i := range lin2sRGBLUT[:lutSize] {
lin2sRGBLUT[i] = linear2sRGB(float64(i) / lutSize)
}
lin2sRGBLUT[lutSize] = lin2sRGBLUT[lutSize-1]
}
func BenchmarkLinear2sRGB(b *testing.B) {
for i := 0; i < b.N; i++ {
for j := 0.0; j <= 1.0; j += 0.01 {
convert.Linear2sRGB(j)
}
}
}
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基准测试显示，优化后的运行时性能提升约为 98%。
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name old time/op new time/op delta
Linear2sRGB-6 6.38µs ± 0% 0.14µs ± 0% -97.87% (p=0.000 n=10+8)
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