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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/21910 Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com> Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com> TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Martin Möhrmann
Martin Möhrmann
parent
1650ced98f
commit
f0c5b8b9c9
@ -44,27 +44,44 @@ func YCbCrToRGB(y, cb, cr uint8) (uint8, uint8, uint8) {
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// B = Y' + 1.77200*(Cb-128)
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// http://www.w3.org/Graphics/JPEG/jfif3.pdf says Y but means Y'.
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yy1 := int32(y) * 0x10100 // Convert 0x12 to 0x121200.
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yy1 := int32(y) * 0x010100 // Convert 0x12 to 0x121200.
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cb1 := int32(cb) - 128
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cr1 := int32(cr) - 128
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r := (yy1 + 91881*cr1) >> 16
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g := (yy1 - 22554*cb1 - 46802*cr1) >> 16
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b := (yy1 + 116130*cb1) >> 16
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if r < 0 {
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r = 0
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} else if r > 0xff {
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r = 0xff
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// The bit twiddling below is equivalent to
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//
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// r := (yy1 + 91881*cr1) >> 16
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// if r < 0 {
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// r = 0
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// } else if r > 0xff {
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// r = ^int32(0)
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// }
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//
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// but uses fewer branches and is faster.
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// Note that the uint8 type conversion in the return
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// statement will convert ^int32(0) to 0xff.
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// The code below to compute b and g uses a similar pattern.
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r := yy1 + 91881*cr1
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if uint32(r)&0xff000000 == 0 {
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r >>= 16
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} else {
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r = ^(r >> 31)
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}
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if g < 0 {
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g = 0
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} else if g > 0xff {
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g = 0xff
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b := yy1 + 116130*cb1
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if uint32(b)&0xff000000 == 0 {
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b >>= 16
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} else {
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b = ^(b >> 31)
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}
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if b < 0 {
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b = 0
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} else if b > 0xff {
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b = 0xff
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g := yy1 - 22554*cb1 - 46802*cr1
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if uint32(g)&0xff000000 == 0 {
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g >>= 16
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} else {
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g = ^(g >> 31)
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}
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return uint8(r), uint8(g), uint8(b)
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}
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@ -95,26 +95,42 @@ const sratioCase = `
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%s
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// This is an inline version of image/color/ycbcr.go's func YCbCrToRGB.
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yy1 := int32(src.Y[yi]) * 0x10100 // Convert 0x12 to 0x121200.
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yy1 := int32(src.Y[yi]) * 0x010100 // Convert 0x12 to 0x121200.
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cb1 := int32(src.Cb[ci]) - 128
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cr1 := int32(src.Cr[ci]) - 128
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r := (yy1 + 91881*cr1) >> 16
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g := (yy1 - 22554*cb1 - 46802*cr1) >> 16
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b := (yy1 + 116130*cb1) >> 16
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if r < 0 {
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r = 0
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} else if r > 255 {
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r = 255
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// The bit twiddling below is equivalent to
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//
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// r := (yy1 + 91881*cr1) >> 16
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// if r < 0 {
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// r = 0
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// } else if r > 0xff {
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// r = ^int32(0)
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// }
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//
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// but uses fewer branches and is faster.
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// Note that the uint8 type conversion in the return
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// statement will convert ^int32(0) to 0xff.
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// The code below to compute b and g uses a similar pattern.
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r := yy1 + 91881*cr1
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if uint32(r)&0xff000000 == 0 {
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r >>= 16
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} else {
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r = ^(r >> 31)
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}
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if g < 0 {
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g = 0
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} else if g > 255 {
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g = 255
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b := yy1 + 116130*cb1
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if uint32(b)&0xff000000 == 0 {
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b >>= 16
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} else {
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b = ^(b >> 31)
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}
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if b < 0 {
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b = 0
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} else if b > 255 {
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b = 255
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g := yy1 - 22554*cb1 - 46802*cr1
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if uint32(g)&0xff000000 == 0 {
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g >>= 16
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} else {
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g = ^(g >> 31)
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}
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dpix[x+0] = uint8(r)
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@ -44,26 +44,42 @@ func DrawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Po
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for x := x0; x != x1; x, yi, ci = x+4, yi+1, ci+1 {
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// This is an inline version of image/color/ycbcr.go's func YCbCrToRGB.
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yy1 := int32(src.Y[yi]) * 0x10100 // Convert 0x12 to 0x121200.
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yy1 := int32(src.Y[yi]) * 0x010100 // Convert 0x12 to 0x121200.
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cb1 := int32(src.Cb[ci]) - 128
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cr1 := int32(src.Cr[ci]) - 128
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r := (yy1 + 91881*cr1) >> 16
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g := (yy1 - 22554*cb1 - 46802*cr1) >> 16
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b := (yy1 + 116130*cb1) >> 16
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if r < 0 {
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r = 0
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} else if r > 255 {
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r = 255
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// The bit twiddling below is equivalent to
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//
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// r := (yy1 + 91881*cr1) >> 16
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// if r < 0 {
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// r = 0
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// } else if r > 0xff {
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// r = ^int32(0)
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// }
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//
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// but uses fewer branches and is faster.
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// Note that the uint8 type conversion in the return
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// statement will convert ^int32(0) to 0xff.
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// The code below to compute b and g uses a similar pattern.
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r := yy1 + 91881*cr1
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if uint32(r)&0xff000000 == 0 {
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r >>= 16
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} else {
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r = ^(r >> 31)
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}
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if g < 0 {
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g = 0
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} else if g > 255 {
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g = 255
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b := yy1 + 116130*cb1
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if uint32(b)&0xff000000 == 0 {
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b >>= 16
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} else {
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b = ^(b >> 31)
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}
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if b < 0 {
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b = 0
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} else if b > 255 {
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b = 255
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g := yy1 - 22554*cb1 - 46802*cr1
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if uint32(g)&0xff000000 == 0 {
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g >>= 16
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} else {
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g = ^(g >> 31)
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}
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dpix[x+0] = uint8(r)
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@ -83,26 +99,42 @@ func DrawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Po
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ci := ciBase + sx/2
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// This is an inline version of image/color/ycbcr.go's func YCbCrToRGB.
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yy1 := int32(src.Y[yi]) * 0x10100 // Convert 0x12 to 0x121200.
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yy1 := int32(src.Y[yi]) * 0x010100 // Convert 0x12 to 0x121200.
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cb1 := int32(src.Cb[ci]) - 128
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cr1 := int32(src.Cr[ci]) - 128
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r := (yy1 + 91881*cr1) >> 16
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g := (yy1 - 22554*cb1 - 46802*cr1) >> 16
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b := (yy1 + 116130*cb1) >> 16
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if r < 0 {
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r = 0
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} else if r > 255 {
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r = 255
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// The bit twiddling below is equivalent to
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//
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// r := (yy1 + 91881*cr1) >> 16
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// if r < 0 {
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// r = 0
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// } else if r > 0xff {
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// r = ^int32(0)
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// }
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//
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// but uses fewer branches and is faster.
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// Note that the uint8 type conversion in the return
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// statement will convert ^int32(0) to 0xff.
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// The code below to compute b and g uses a similar pattern.
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r := yy1 + 91881*cr1
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if uint32(r)&0xff000000 == 0 {
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r >>= 16
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} else {
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r = ^(r >> 31)
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}
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if g < 0 {
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g = 0
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} else if g > 255 {
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g = 255
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b := yy1 + 116130*cb1
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if uint32(b)&0xff000000 == 0 {
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b >>= 16
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} else {
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b = ^(b >> 31)
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}
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if b < 0 {
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b = 0
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} else if b > 255 {
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b = 255
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g := yy1 - 22554*cb1 - 46802*cr1
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if uint32(g)&0xff000000 == 0 {
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g >>= 16
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} else {
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g = ^(g >> 31)
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}
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dpix[x+0] = uint8(r)
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@ -122,26 +154,42 @@ func DrawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Po
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ci := ciBase + sx/2
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// This is an inline version of image/color/ycbcr.go's func YCbCrToRGB.
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yy1 := int32(src.Y[yi]) * 0x10100 // Convert 0x12 to 0x121200.
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yy1 := int32(src.Y[yi]) * 0x010100 // Convert 0x12 to 0x121200.
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cb1 := int32(src.Cb[ci]) - 128
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cr1 := int32(src.Cr[ci]) - 128
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r := (yy1 + 91881*cr1) >> 16
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g := (yy1 - 22554*cb1 - 46802*cr1) >> 16
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b := (yy1 + 116130*cb1) >> 16
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if r < 0 {
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r = 0
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} else if r > 255 {
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r = 255
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// The bit twiddling below is equivalent to
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//
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// r := (yy1 + 91881*cr1) >> 16
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// if r < 0 {
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// r = 0
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// } else if r > 0xff {
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// r = ^int32(0)
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// }
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//
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// but uses fewer branches and is faster.
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// Note that the uint8 type conversion in the return
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// statement will convert ^int32(0) to 0xff.
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// The code below to compute b and g uses a similar pattern.
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r := yy1 + 91881*cr1
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if uint32(r)&0xff000000 == 0 {
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r >>= 16
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} else {
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r = ^(r >> 31)
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}
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if g < 0 {
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g = 0
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} else if g > 255 {
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g = 255
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b := yy1 + 116130*cb1
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if uint32(b)&0xff000000 == 0 {
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b >>= 16
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} else {
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b = ^(b >> 31)
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}
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if b < 0 {
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b = 0
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} else if b > 255 {
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b = 255
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g := yy1 - 22554*cb1 - 46802*cr1
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if uint32(g)&0xff000000 == 0 {
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g >>= 16
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} else {
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g = ^(g >> 31)
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}
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dpix[x+0] = uint8(r)
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@ -160,26 +208,42 @@ func DrawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Po
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for x := x0; x != x1; x, yi, ci = x+4, yi+1, ci+1 {
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// This is an inline version of image/color/ycbcr.go's func YCbCrToRGB.
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yy1 := int32(src.Y[yi]) * 0x10100 // Convert 0x12 to 0x121200.
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yy1 := int32(src.Y[yi]) * 0x010100 // Convert 0x12 to 0x121200.
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cb1 := int32(src.Cb[ci]) - 128
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cr1 := int32(src.Cr[ci]) - 128
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r := (yy1 + 91881*cr1) >> 16
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g := (yy1 - 22554*cb1 - 46802*cr1) >> 16
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b := (yy1 + 116130*cb1) >> 16
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if r < 0 {
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r = 0
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} else if r > 255 {
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r = 255
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// The bit twiddling below is equivalent to
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//
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// r := (yy1 + 91881*cr1) >> 16
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// if r < 0 {
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// r = 0
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// } else if r > 0xff {
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// r = ^int32(0)
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// }
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//
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// but uses fewer branches and is faster.
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// Note that the uint8 type conversion in the return
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// statement will convert ^int32(0) to 0xff.
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// The code below to compute b and g uses a similar pattern.
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r := yy1 + 91881*cr1
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if uint32(r)&0xff000000 == 0 {
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r >>= 16
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} else {
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r = ^(r >> 31)
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}
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if g < 0 {
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g = 0
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} else if g > 255 {
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g = 255
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b := yy1 + 116130*cb1
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if uint32(b)&0xff000000 == 0 {
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b >>= 16
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} else {
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b = ^(b >> 31)
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}
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if b < 0 {
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b = 0
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} else if b > 255 {
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b = 255
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g := yy1 - 22554*cb1 - 46802*cr1
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if uint32(g)&0xff000000 == 0 {
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g >>= 16
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} else {
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g = ^(g >> 31)
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}
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dpix[x+0] = uint8(r)
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