image/color: order color computation to match rgb

The order of computation was switched unintentionally
in https://go-review.googlesource.com/21910.

Revert the order to first compute g then b.

Change-Id: I8cedb5e45fbad2679246839f609bcac4f9052403
Reviewed-on: https://go-review.googlesource.com/22016
Reviewed-by: Nigel Tao <nigeltao@golang.org>

3 files changed, 48 insertions, 48 deletions

diff --git a/src/image/color/ycbcr.go b/src/image/color/ycbcr.go
index 2e985fece1..55549c3fce 100644
--- a/src/image/color/ycbcr.go
+++ b/src/image/color/ycbcr.go
@@ -60,7 +60,7 @@ func YCbCrToRGB(y, cb, cr uint8) (uint8, uint8, uint8) {
 	// 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.
+	// The code below to compute g and b uses a similar pattern.
 	r := yy1 + 91881*cr1
 	if uint32(r)&0xff000000 == 0 {
 		r >>= 16
@@ -68,13 +68,6 @@ func YCbCrToRGB(y, cb, cr uint8) (uint8, uint8, uint8) {
 		r = ^(r >> 31)
 	}
 
-	b := yy1 + 116130*cb1
-	if uint32(b)&0xff000000 == 0 {
-		b >>= 16
-	} else {
-		b = ^(b >> 31)
-	}
-
 	g := yy1 - 22554*cb1 - 46802*cr1
 	if uint32(g)&0xff000000 == 0 {
 		g >>= 16
@@ -82,6 +75,13 @@ func YCbCrToRGB(y, cb, cr uint8) (uint8, uint8, uint8) {
 		g = ^(g >> 31)
 	}
 
+	b := yy1 + 116130*cb1
+	if uint32(b)&0xff000000 == 0 {
+		b >>= 16
+	} else {
+		b = ^(b >> 31)
+	}
+
 	return uint8(r), uint8(g), uint8(b)
 }
 
diff --git a/src/image/internal/imageutil/gen.go b/src/image/internal/imageutil/gen.go
index 6f8d2b2f5d..b9158d0ce9 100644
--- a/src/image/internal/imageutil/gen.go
+++ b/src/image/internal/imageutil/gen.go
@@ -111,7 +111,7 @@ const sratioCase = `
 				// 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.
+				// The code below to compute g and b uses a similar pattern.
 				r := yy1 + 91881*cr1
 				if uint32(r)&0xff000000 == 0 {
 					r >>= 16
@@ -119,13 +119,6 @@ const sratioCase = `
 					r = ^(r >> 31)
 				}
 
-				b := yy1 + 116130*cb1
-				if uint32(b)&0xff000000 == 0 {
-					b >>= 16
-				} else {
-					b = ^(b >> 31)
-				}
-
 				g := yy1 - 22554*cb1 - 46802*cr1
 				if uint32(g)&0xff000000 == 0 {
 					g >>= 16
@@ -133,6 +126,13 @@ const sratioCase = `
 					g = ^(g >> 31)
 				}
 
+				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)
diff --git a/src/image/internal/imageutil/impl.go b/src/image/internal/imageutil/impl.go
index 0993f3145c..39b455fdfa 100644
--- a/src/image/internal/imageutil/impl.go
+++ b/src/image/internal/imageutil/impl.go
@@ -60,7 +60,7 @@ func DrawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Po
 				// 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.
+				// The code below to compute g and b uses a similar pattern.
 				r := yy1 + 91881*cr1
 				if uint32(r)&0xff000000 == 0 {
 					r >>= 16
@@ -68,13 +68,6 @@ func DrawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Po
 					r = ^(r >> 31)
 				}
 
-				b := yy1 + 116130*cb1
-				if uint32(b)&0xff000000 == 0 {
-					b >>= 16
-				} else {
-					b = ^(b >> 31)
-				}
-
 				g := yy1 - 22554*cb1 - 46802*cr1
 				if uint32(g)&0xff000000 == 0 {
 					g >>= 16
@@ -82,6 +75,13 @@ func DrawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Po
 					g = ^(g >> 31)
 				}
 
+				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)
@@ -115,7 +115,7 @@ func DrawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Po
 				// 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.
+				// The code below to compute g and b uses a similar pattern.
 				r := yy1 + 91881*cr1
 				if uint32(r)&0xff000000 == 0 {
 					r >>= 16
@@ -123,13 +123,6 @@ func DrawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Po
 					r = ^(r >> 31)
 				}
 
-				b := yy1 + 116130*cb1
-				if uint32(b)&0xff000000 == 0 {
-					b >>= 16
-				} else {
-					b = ^(b >> 31)
-				}
-
 				g := yy1 - 22554*cb1 - 46802*cr1
 				if uint32(g)&0xff000000 == 0 {
 					g >>= 16
@@ -137,6 +130,13 @@ func DrawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Po
 					g = ^(g >> 31)
 				}
 
+				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)
@@ -170,7 +170,7 @@ func DrawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Po
 				// 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.
+				// The code below to compute g and b uses a similar pattern.
 				r := yy1 + 91881*cr1
 				if uint32(r)&0xff000000 == 0 {
 					r >>= 16
@@ -178,13 +178,6 @@ func DrawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Po
 					r = ^(r >> 31)
 				}
 
-				b := yy1 + 116130*cb1
-				if uint32(b)&0xff000000 == 0 {
-					b >>= 16
-				} else {
-					b = ^(b >> 31)
-				}
-
 				g := yy1 - 22554*cb1 - 46802*cr1
 				if uint32(g)&0xff000000 == 0 {
 					g >>= 16
@@ -192,6 +185,13 @@ func DrawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Po
 					g = ^(g >> 31)
 				}
 
+				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)
@@ -224,7 +224,7 @@ func DrawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Po
 				// 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.
+				// The code below to compute g and b uses a similar pattern.
 				r := yy1 + 91881*cr1
 				if uint32(r)&0xff000000 == 0 {
 					r >>= 16
@@ -232,13 +232,6 @@ func DrawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Po
 					r = ^(r >> 31)
 				}
 
-				b := yy1 + 116130*cb1
-				if uint32(b)&0xff000000 == 0 {
-					b >>= 16
-				} else {
-					b = ^(b >> 31)
-				}
-
 				g := yy1 - 22554*cb1 - 46802*cr1
 				if uint32(g)&0xff000000 == 0 {
 					g >>= 16
@@ -246,6 +239,13 @@ func DrawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Po
 					g = ^(g >> 31)
 				}
 
+				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)