diff options
Diffstat (limited to 'libgo/go/image/internal/imageutil/impl.go')
| -rw-r--r-- | libgo/go/image/internal/imageutil/impl.go | 232 |
1 files changed, 152 insertions, 80 deletions
diff --git a/libgo/go/image/internal/imageutil/impl.go b/libgo/go/image/internal/imageutil/impl.go index fd7826d4a9..3696b08e41 100644 --- a/libgo/go/image/internal/imageutil/impl.go +++ b/libgo/go/image/internal/imageutil/impl.go @@ -44,32 +44,50 @@ 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 g and b 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 + + g := yy1 - 22554*cb1 - 46802*cr1 + if uint32(g)&0xff000000 == 0 { + g >>= 16 + } else { + g = ^(g >> 31) } - if b < 0 { - b = 0 - } else if b > 255 { - b = 255 + + b := yy1 + 116130*cb1 + if uint32(b)&0xff000000 == 0 { + b >>= 16 + } else { + b = ^(b >> 31) } - dpix[x+0] = uint8(r) - dpix[x+1] = uint8(g) - dpix[x+2] = uint8(b) - dpix[x+3] = 255 + // use a temp slice to hint to the compiler that a single bounds check suffices + rgba := dpix[x : x+4 : len(dpix)] + rgba[0] = uint8(r) + rgba[1] = uint8(g) + rgba[2] = uint8(b) + rgba[3] = 255 } } @@ -83,32 +101,50 @@ 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 g and b 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 + + g := yy1 - 22554*cb1 - 46802*cr1 + if uint32(g)&0xff000000 == 0 { + g >>= 16 + } else { + g = ^(g >> 31) } - if b < 0 { - b = 0 - } else if b > 255 { - b = 255 + + b := yy1 + 116130*cb1 + if uint32(b)&0xff000000 == 0 { + b >>= 16 + } else { + b = ^(b >> 31) } - dpix[x+0] = uint8(r) - dpix[x+1] = uint8(g) - dpix[x+2] = uint8(b) - dpix[x+3] = 255 + // use a temp slice to hint to the compiler that a single bounds check suffices + rgba := dpix[x : x+4 : len(dpix)] + rgba[0] = uint8(r) + rgba[1] = uint8(g) + rgba[2] = uint8(b) + rgba[3] = 255 } } @@ -122,32 +158,50 @@ 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 g and b 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 + + g := yy1 - 22554*cb1 - 46802*cr1 + if uint32(g)&0xff000000 == 0 { + g >>= 16 + } else { + g = ^(g >> 31) } - if b < 0 { - b = 0 - } else if b > 255 { - b = 255 + + b := yy1 + 116130*cb1 + if uint32(b)&0xff000000 == 0 { + b >>= 16 + } else { + b = ^(b >> 31) } - dpix[x+0] = uint8(r) - dpix[x+1] = uint8(g) - dpix[x+2] = uint8(b) - dpix[x+3] = 255 + // use a temp slice to hint to the compiler that a single bounds check suffices + rgba := dpix[x : x+4 : len(dpix)] + rgba[0] = uint8(r) + rgba[1] = uint8(g) + rgba[2] = uint8(b) + rgba[3] = 255 } } @@ -160,32 +214,50 @@ 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 g and b 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 + + g := yy1 - 22554*cb1 - 46802*cr1 + if uint32(g)&0xff000000 == 0 { + g >>= 16 + } else { + g = ^(g >> 31) } - if b < 0 { - b = 0 - } else if b > 255 { - b = 255 + + b := yy1 + 116130*cb1 + if uint32(b)&0xff000000 == 0 { + b >>= 16 + } else { + b = ^(b >> 31) } - dpix[x+0] = uint8(r) - dpix[x+1] = uint8(g) - dpix[x+2] = uint8(b) - dpix[x+3] = 255 + // use a temp slice to hint to the compiler that a single bounds check suffices + rgba := dpix[x : x+4 : len(dpix)] + rgba[0] = uint8(r) + rgba[1] = uint8(g) + rgba[2] = uint8(b) + rgba[3] = 255 } } |