1 files changed, 82 insertions, 0 deletions
diff --git a/src/pkg/image/jpeg/writer_test.go b/src/pkg/image/jpeg/writer_test.go
index b8e8fa34e1..8732df8459 100644
--- a/src/pkg/image/jpeg/writer_test.go
+++ b/src/pkg/image/jpeg/writer_test.go
@@ -6,6 +6,7 @@ package jpeg
 
 import (
 	"bytes"
+	"fmt"
 	"image"
 	"image/color"
 	"image/png"
@@ -15,6 +16,87 @@ import (
 	"testing"
 )
 
+// zigzag maps from the natural ordering to the zig-zag ordering. For example,
+// zigzag[0*8 + 3] is the zig-zag sequence number of the element in the fourth
+// column and first row.
+var zigzag = [blockSize]int{
+	0, 1, 5, 6, 14, 15, 27, 28,
+	2, 4, 7, 13, 16, 26, 29, 42,
+	3, 8, 12, 17, 25, 30, 41, 43,
+	9, 11, 18, 24, 31, 40, 44, 53,
+	10, 19, 23, 32, 39, 45, 52, 54,
+	20, 22, 33, 38, 46, 51, 55, 60,
+	21, 34, 37, 47, 50, 56, 59, 61,
+	35, 36, 48, 49, 57, 58, 62, 63,
+}
+
+func TestZigUnzig(t *testing.T) {
+	for i := 0; i < blockSize; i++ {
+		if unzig[zigzag[i]] != i {
+			t.Errorf("unzig[zigzag[%d]] == %d", i, unzig[zigzag[i]])
+		}
+		if zigzag[unzig[i]] != i {
+			t.Errorf("zigzag[unzig[%d]] == %d", i, zigzag[unzig[i]])
+		}
+	}
+}
+
+// unscaledQuantInNaturalOrder are the unscaled quantization tables in
+// natural (not zig-zag) order, as specified in section K.1.
+var unscaledQuantInNaturalOrder = [nQuantIndex][blockSize]byte{
+	// Luminance.
+	{
+		16, 11, 10, 16, 24, 40, 51, 61,
+		12, 12, 14, 19, 26, 58, 60, 55,
+		14, 13, 16, 24, 40, 57, 69, 56,
+		14, 17, 22, 29, 51, 87, 80, 62,
+		18, 22, 37, 56, 68, 109, 103, 77,
+		24, 35, 55, 64, 81, 104, 113, 92,
+		49, 64, 78, 87, 103, 121, 120, 101,
+		72, 92, 95, 98, 112, 100, 103, 99,
+	},
+	// Chrominance.
+	{
+		17, 18, 24, 47, 99, 99, 99, 99,
+		18, 21, 26, 66, 99, 99, 99, 99,
+		24, 26, 56, 99, 99, 99, 99, 99,
+		47, 66, 99, 99, 99, 99, 99, 99,
+		99, 99, 99, 99, 99, 99, 99, 99,
+		99, 99, 99, 99, 99, 99, 99, 99,
+		99, 99, 99, 99, 99, 99, 99, 99,
+		99, 99, 99, 99, 99, 99, 99, 99,
+	},
+}
+
+func TestUnscaledQuant(t *testing.T) {
+	bad := false
+	for i := quantIndex(0); i < nQuantIndex; i++ {
+		for zig := 0; zig < blockSize; zig++ {
+			got := unscaledQuant[i][zig]
+			want := unscaledQuantInNaturalOrder[i][unzig[zig]]
+			if got != want {
+				t.Errorf("i=%d, zig=%d: got %d, want %d", i, zig, got, want)
+				bad = true
+			}
+		}
+	}
+	if bad {
+		names := [nQuantIndex]string{"Luminance", "Chrominance"}
+		buf := &bytes.Buffer{}
+		for i, name := range names {
+			fmt.Fprintf(buf, "// %s.\n{\n", name)
+			for zig := 0; zig < blockSize; zig++ {
+				fmt.Fprintf(buf, "%d, ", unscaledQuantInNaturalOrder[i][unzig[zig]])
+				if zig%8 == 7 {
+					buf.WriteString("\n")
+				}
+			}
+			buf.WriteString("},\n")
+		}
+		t.Logf("expected unscaledQuant values:\n%s", buf.String())
+	}
+}
+
 var testCase = []struct {
 	filename  string
 	quality   int