aboutsummaryrefslogtreecommitdiff
path: root/vendor/golang.org/x/image/vp8/idct.go
diff options
context:
space:
mode:
Diffstat (limited to 'vendor/golang.org/x/image/vp8/idct.go')
-rw-r--r--vendor/golang.org/x/image/vp8/idct.go98
1 files changed, 98 insertions, 0 deletions
diff --git a/vendor/golang.org/x/image/vp8/idct.go b/vendor/golang.org/x/image/vp8/idct.go
new file mode 100644
index 0000000..929af2c
--- /dev/null
+++ b/vendor/golang.org/x/image/vp8/idct.go
@@ -0,0 +1,98 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package vp8
+
+// This file implements the inverse Discrete Cosine Transform and the inverse
+// Walsh Hadamard Transform (WHT), as specified in sections 14.3 and 14.4.
+
+func clip8(i int32) uint8 {
+ if i < 0 {
+ return 0
+ }
+ if i > 255 {
+ return 255
+ }
+ return uint8(i)
+}
+
+func (z *Decoder) inverseDCT4(y, x, coeffBase int) {
+ const (
+ c1 = 85627 // 65536 * cos(pi/8) * sqrt(2).
+ c2 = 35468 // 65536 * sin(pi/8) * sqrt(2).
+ )
+ var m [4][4]int32
+ for i := 0; i < 4; i++ {
+ a := int32(z.coeff[coeffBase+0]) + int32(z.coeff[coeffBase+8])
+ b := int32(z.coeff[coeffBase+0]) - int32(z.coeff[coeffBase+8])
+ c := (int32(z.coeff[coeffBase+4])*c2)>>16 - (int32(z.coeff[coeffBase+12])*c1)>>16
+ d := (int32(z.coeff[coeffBase+4])*c1)>>16 + (int32(z.coeff[coeffBase+12])*c2)>>16
+ m[i][0] = a + d
+ m[i][1] = b + c
+ m[i][2] = b - c
+ m[i][3] = a - d
+ coeffBase++
+ }
+ for j := 0; j < 4; j++ {
+ dc := m[0][j] + 4
+ a := dc + m[2][j]
+ b := dc - m[2][j]
+ c := (m[1][j]*c2)>>16 - (m[3][j]*c1)>>16
+ d := (m[1][j]*c1)>>16 + (m[3][j]*c2)>>16
+ z.ybr[y+j][x+0] = clip8(int32(z.ybr[y+j][x+0]) + (a+d)>>3)
+ z.ybr[y+j][x+1] = clip8(int32(z.ybr[y+j][x+1]) + (b+c)>>3)
+ z.ybr[y+j][x+2] = clip8(int32(z.ybr[y+j][x+2]) + (b-c)>>3)
+ z.ybr[y+j][x+3] = clip8(int32(z.ybr[y+j][x+3]) + (a-d)>>3)
+ }
+}
+
+func (z *Decoder) inverseDCT4DCOnly(y, x, coeffBase int) {
+ dc := (int32(z.coeff[coeffBase+0]) + 4) >> 3
+ for j := 0; j < 4; j++ {
+ for i := 0; i < 4; i++ {
+ z.ybr[y+j][x+i] = clip8(int32(z.ybr[y+j][x+i]) + dc)
+ }
+ }
+}
+
+func (z *Decoder) inverseDCT8(y, x, coeffBase int) {
+ z.inverseDCT4(y+0, x+0, coeffBase+0*16)
+ z.inverseDCT4(y+0, x+4, coeffBase+1*16)
+ z.inverseDCT4(y+4, x+0, coeffBase+2*16)
+ z.inverseDCT4(y+4, x+4, coeffBase+3*16)
+}
+
+func (z *Decoder) inverseDCT8DCOnly(y, x, coeffBase int) {
+ z.inverseDCT4DCOnly(y+0, x+0, coeffBase+0*16)
+ z.inverseDCT4DCOnly(y+0, x+4, coeffBase+1*16)
+ z.inverseDCT4DCOnly(y+4, x+0, coeffBase+2*16)
+ z.inverseDCT4DCOnly(y+4, x+4, coeffBase+3*16)
+}
+
+func (d *Decoder) inverseWHT16() {
+ var m [16]int32
+ for i := 0; i < 4; i++ {
+ a0 := int32(d.coeff[384+0+i]) + int32(d.coeff[384+12+i])
+ a1 := int32(d.coeff[384+4+i]) + int32(d.coeff[384+8+i])
+ a2 := int32(d.coeff[384+4+i]) - int32(d.coeff[384+8+i])
+ a3 := int32(d.coeff[384+0+i]) - int32(d.coeff[384+12+i])
+ m[0+i] = a0 + a1
+ m[8+i] = a0 - a1
+ m[4+i] = a3 + a2
+ m[12+i] = a3 - a2
+ }
+ out := 0
+ for i := 0; i < 4; i++ {
+ dc := m[0+i*4] + 3
+ a0 := dc + m[3+i*4]
+ a1 := m[1+i*4] + m[2+i*4]
+ a2 := m[1+i*4] - m[2+i*4]
+ a3 := dc - m[3+i*4]
+ d.coeff[out+0] = int16((a0 + a1) >> 3)
+ d.coeff[out+16] = int16((a3 + a2) >> 3)
+ d.coeff[out+32] = int16((a0 - a1) >> 3)
+ d.coeff[out+48] = int16((a3 - a2) >> 3)
+ out += 64
+ }
+}