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Commit f0c5b8b9 authored by Martin Möhrmann's avatar Martin Möhrmann Committed by Martin Möhrmann
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image/color: optimize YCbCrToRGB 

Use one comparison to detect underflow and overflow simultaneously.
Use a shift, bitwise complement and uint8 type conversion to handle
clamping to upper and lower bound without additional branching.

Overall the new code is faster for a mix of
common case, underflow and overflow.

name     old time/op  new time/op  delta
YCbCr-2  1.12ms ± 0%  0.64ms ± 0%  -43.01%  (p=0.000 n=48+47)

name              old time/op  new time/op  delta
YCbCrToRGB/0-2    5.52ns ± 0%  5.77ns ± 0%  +4.48%  (p=0.000 n=50+49)
YCbCrToRGB/128-2  6.05ns ± 0%  5.52ns ± 0%  -8.69%  (p=0.000 n=39+50)
YCbCrToRGB/255-2  5.80ns ± 0%  5.77ns ± 0%  -0.58%  (p=0.000 n=50+49)

Found in collaboration with Josh Bleecher Snyder and Ralph Corderoy.

Change-Id: Ic5020320f704966f545fdc1ae6bc24ddb5d3d09a
Reviewed-on: https://go-review.googlesource.com/21910Reviewed-by: 's avatarJosh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
parent 1650ced9
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Showing with 193 additions and 96 deletions
src/image/color/ycbcr.go
View file @ f0c5b8b9
......@@ -44,27 +44,44 @@ func YCbCrToRGB(y, cb, cr uint8) (uint8, uint8, uint8) {
// B = Y' + 1.77200*(Cb-128)
// http://www.w3.org/Graphics/JPEG/jfif3.pdf says Y but means Y'.
yy1 := int32(y) * 0x10100 // Convert 0x12 to 0x121200.
yy1 := int32(y) * 0x010100 // Convert 0x12 to 0x121200.
cb1 := int32(cb) - 128
cr1 := int32(cr) - 128
r := (yy1 + 91881*cr1) >> 16
g := (yy1 - 22554*cb1 - 46802*cr1) >> 16
b := (yy1 + 116130*cb1) >> 16
if r < 0 {
r = 0
} else if r > 0xff {
r = 0xff
// The bit twiddling below is equivalent to
//
// r := (yy1 + 91881*cr1) >> 16
// if r < 0 {
// r = 0
// } else if r > 0xff {
// r = ^int32(0)
// }
//
// but uses fewer branches and is faster.
// Note that the uint8 type conversion in the return
// statement will convert ^int32(0) to 0xff.
// The code below to compute b and g uses a similar pattern.
r := yy1 + 91881*cr1
if uint32(r)&0xff000000 == 0 {
r >>= 16
} else {
r = ^(r >> 31)
}
if g < 0 {
g = 0
} else if g > 0xff {
g = 0xff
b := yy1 + 116130*cb1
if uint32(b)&0xff000000 == 0 {
b >>= 16
} else {
b = ^(b >> 31)
}
if b < 0 {
b = 0
} else if b > 0xff {
b = 0xff
g := yy1 - 22554*cb1 - 46802*cr1
if uint32(g)&0xff000000 == 0 {
g >>= 16
} else {
g = ^(g >> 31)
}
return uint8(r), uint8(g), uint8(b)
}
......
src/image/internal/imageutil/gen.go
View file @ f0c5b8b9
......@@ -95,26 +95,42 @@ const sratioCase = `
%s
// This is an inline version of image/color/ycbcr.go's func YCbCrToRGB.
yy1 := int32(src.Y[yi]) * 0x10100 // Convert 0x12 to 0x121200.
yy1 := int32(src.Y[yi]) * 0x010100 // Convert 0x12 to 0x121200.
cb1 := int32(src.Cb[ci]) - 128
cr1 := int32(src.Cr[ci]) - 128
r := (yy1 + 91881*cr1) >> 16
g := (yy1 - 22554*cb1 - 46802*cr1) >> 16
b := (yy1 + 116130*cb1) >> 16
if r < 0 {
r = 0
} else if r > 255 {
r = 255
// The bit twiddling below is equivalent to
//
// r := (yy1 + 91881*cr1) >> 16
// if r < 0 {
// r = 0
// } else if r > 0xff {
// r = ^int32(0)
// }
//
// but uses fewer branches and is faster.
// Note that the uint8 type conversion in the return
// statement will convert ^int32(0) to 0xff.
// The code below to compute b and g uses a similar pattern.
r := yy1 + 91881*cr1
if uint32(r)&0xff000000 == 0 {
r >>= 16
} else {
r = ^(r >> 31)
}
if g < 0 {
g = 0
} else if g > 255 {
g = 255
b := yy1 + 116130*cb1
if uint32(b)&0xff000000 == 0 {
b >>= 16
} else {
b = ^(b >> 31)
}
if b < 0 {
b = 0
} else if b > 255 {
b = 255
g := yy1 - 22554*cb1 - 46802*cr1
if uint32(g)&0xff000000 == 0 {
g >>= 16
} else {
g = ^(g >> 31)
}
dpix[x+0] = uint8(r)
......
src/image/internal/imageutil/impl.go
View file @ f0c5b8b9
......@@ -44,26 +44,42 @@ func DrawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Po
for x := x0; x != x1; x, yi, ci = x+4, yi+1, ci+1 {
// This is an inline version of image/color/ycbcr.go's func YCbCrToRGB.
yy1 := int32(src.Y[yi]) * 0x10100 // Convert 0x12 to 0x121200.
yy1 := int32(src.Y[yi]) * 0x010100 // Convert 0x12 to 0x121200.
cb1 := int32(src.Cb[ci]) - 128
cr1 := int32(src.Cr[ci]) - 128
r := (yy1 + 91881*cr1) >> 16
g := (yy1 - 22554*cb1 - 46802*cr1) >> 16
b := (yy1 + 116130*cb1) >> 16
if r < 0 {
r = 0
} else if r > 255 {
r = 255
// The bit twiddling below is equivalent to
//
// r := (yy1 + 91881*cr1) >> 16
// if r < 0 {
// r = 0
// } else if r > 0xff {
// r = ^int32(0)
// }
//
// but uses fewer branches and is faster.
// Note that the uint8 type conversion in the return
// statement will convert ^int32(0) to 0xff.
// The code below to compute b and g uses a similar pattern.
r := yy1 + 91881*cr1
if uint32(r)&0xff000000 == 0 {
r >>= 16
} else {
r = ^(r >> 31)
}
if g < 0 {
g = 0
} else if g > 255 {
g = 255
b := yy1 + 116130*cb1
if uint32(b)&0xff000000 == 0 {
b >>= 16
} else {
b = ^(b >> 31)
}
if b < 0 {
b = 0
} else if b > 255 {
b = 255
g := yy1 - 22554*cb1 - 46802*cr1
if uint32(g)&0xff000000 == 0 {
g >>= 16
} else {
g = ^(g >> 31)
}
dpix[x+0] = uint8(r)
......@@ -83,26 +99,42 @@ func DrawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Po
ci := ciBase + sx/2
// This is an inline version of image/color/ycbcr.go's func YCbCrToRGB.
yy1 := int32(src.Y[yi]) * 0x10100 // Convert 0x12 to 0x121200.
yy1 := int32(src.Y[yi]) * 0x010100 // Convert 0x12 to 0x121200.
cb1 := int32(src.Cb[ci]) - 128
cr1 := int32(src.Cr[ci]) - 128
r := (yy1 + 91881*cr1) >> 16
g := (yy1 - 22554*cb1 - 46802*cr1) >> 16
b := (yy1 + 116130*cb1) >> 16
if r < 0 {
r = 0
} else if r > 255 {
r = 255
// The bit twiddling below is equivalent to
//
// r := (yy1 + 91881*cr1) >> 16
// if r < 0 {
// r = 0
// } else if r > 0xff {
// r = ^int32(0)
// }
//
// but uses fewer branches and is faster.
// Note that the uint8 type conversion in the return
// statement will convert ^int32(0) to 0xff.
// The code below to compute b and g uses a similar pattern.
r := yy1 + 91881*cr1
if uint32(r)&0xff000000 == 0 {
r >>= 16
} else {
r = ^(r >> 31)
}
if g < 0 {
g = 0
} else if g > 255 {
g = 255
b := yy1 + 116130*cb1
if uint32(b)&0xff000000 == 0 {
b >>= 16
} else {
b = ^(b >> 31)
}
if b < 0 {
b = 0
} else if b > 255 {
b = 255
g := yy1 - 22554*cb1 - 46802*cr1
if uint32(g)&0xff000000 == 0 {
g >>= 16
} else {
g = ^(g >> 31)
}
dpix[x+0] = uint8(r)
......@@ -122,26 +154,42 @@ func DrawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Po
ci := ciBase + sx/2
// This is an inline version of image/color/ycbcr.go's func YCbCrToRGB.
yy1 := int32(src.Y[yi]) * 0x10100 // Convert 0x12 to 0x121200.
yy1 := int32(src.Y[yi]) * 0x010100 // Convert 0x12 to 0x121200.
cb1 := int32(src.Cb[ci]) - 128
cr1 := int32(src.Cr[ci]) - 128
r := (yy1 + 91881*cr1) >> 16
g := (yy1 - 22554*cb1 - 46802*cr1) >> 16
b := (yy1 + 116130*cb1) >> 16
if r < 0 {
r = 0
} else if r > 255 {
r = 255
// The bit twiddling below is equivalent to
//
// r := (yy1 + 91881*cr1) >> 16
// if r < 0 {
// r = 0
// } else if r > 0xff {
// r = ^int32(0)
// }
//
// but uses fewer branches and is faster.
// Note that the uint8 type conversion in the return
// statement will convert ^int32(0) to 0xff.
// The code below to compute b and g uses a similar pattern.
r := yy1 + 91881*cr1
if uint32(r)&0xff000000 == 0 {
r >>= 16
} else {
r = ^(r >> 31)
}
if g < 0 {
g = 0
} else if g > 255 {
g = 255
b := yy1 + 116130*cb1
if uint32(b)&0xff000000 == 0 {
b >>= 16
} else {
b = ^(b >> 31)
}
if b < 0 {
b = 0
} else if b > 255 {
b = 255
g := yy1 - 22554*cb1 - 46802*cr1
if uint32(g)&0xff000000 == 0 {
g >>= 16
} else {
g = ^(g >> 31)
}
dpix[x+0] = uint8(r)
......@@ -160,26 +208,42 @@ func DrawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Po
for x := x0; x != x1; x, yi, ci = x+4, yi+1, ci+1 {
// This is an inline version of image/color/ycbcr.go's func YCbCrToRGB.
yy1 := int32(src.Y[yi]) * 0x10100 // Convert 0x12 to 0x121200.
yy1 := int32(src.Y[yi]) * 0x010100 // Convert 0x12 to 0x121200.
cb1 := int32(src.Cb[ci]) - 128
cr1 := int32(src.Cr[ci]) - 128
r := (yy1 + 91881*cr1) >> 16
g := (yy1 - 22554*cb1 - 46802*cr1) >> 16
b := (yy1 + 116130*cb1) >> 16
if r < 0 {
r = 0
} else if r > 255 {
r = 255
// The bit twiddling below is equivalent to
//
// r := (yy1 + 91881*cr1) >> 16
// if r < 0 {
// r = 0
// } else if r > 0xff {
// r = ^int32(0)
// }
//
// but uses fewer branches and is faster.
// Note that the uint8 type conversion in the return
// statement will convert ^int32(0) to 0xff.
// The code below to compute b and g uses a similar pattern.
r := yy1 + 91881*cr1
if uint32(r)&0xff000000 == 0 {
r >>= 16
} else {
r = ^(r >> 31)
}
if g < 0 {
g = 0
} else if g > 255 {
g = 255
b := yy1 + 116130*cb1
if uint32(b)&0xff000000 == 0 {
b >>= 16
} else {
b = ^(b >> 31)
}
if b < 0 {
b = 0
} else if b > 255 {
b = 255
g := yy1 - 22554*cb1 - 46802*cr1
if uint32(g)&0xff000000 == 0 {
g >>= 16
} else {
g = ^(g >> 31)
}
dpix[x+0] = uint8(r)
......
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