git clone https://git.lucas.co/go_mono.git
vp8/idct.go (2.8K)
1 // Copyright 2011 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
4
5 package vp8
6
7 // This file implements the inverse Discrete Cosine Transform and the inverse
8 // Walsh Hadamard Transform (WHT), as specified in sections 14.3 and 14.4.
9
10 func clip8(i int32) uint8 {
11 if i < 0 {
12 return 0
13 }
14 if i > 255 {
15 return 255
16 }
17 return uint8(i)
18 }
19
20 func (z *Decoder) inverseDCT4(y, x, coeffBase int) {
21 const (
22 c1 = 85627 // 65536 * cos(pi/8) * sqrt(2).
23 c2 = 35468 // 65536 * sin(pi/8) * sqrt(2).
24 )
25 var m [4][4]int32
26 for i := 0; i < 4; i++ {
27 a := int32(z.coeff[coeffBase+0]) + int32(z.coeff[coeffBase+8])
28 b := int32(z.coeff[coeffBase+0]) - int32(z.coeff[coeffBase+8])
29 c := (int32(z.coeff[coeffBase+4])*c2)>>16 - (int32(z.coeff[coeffBase+12])*c1)>>16
30 d := (int32(z.coeff[coeffBase+4])*c1)>>16 + (int32(z.coeff[coeffBase+12])*c2)>>16
31 m[i][0] = a + d
32 m[i][1] = b + c
33 m[i][2] = b - c
34 m[i][3] = a - d
35 coeffBase++
36 }
37 for j := 0; j < 4; j++ {
38 dc := m[0][j] + 4
39 a := dc + m[2][j]
40 b := dc - m[2][j]
41 c := (m[1][j]*c2)>>16 - (m[3][j]*c1)>>16
42 d := (m[1][j]*c1)>>16 + (m[3][j]*c2)>>16
43 z.ybr[y+j][x+0] = clip8(int32(z.ybr[y+j][x+0]) + (a+d)>>3)
44 z.ybr[y+j][x+1] = clip8(int32(z.ybr[y+j][x+1]) + (b+c)>>3)
45 z.ybr[y+j][x+2] = clip8(int32(z.ybr[y+j][x+2]) + (b-c)>>3)
46 z.ybr[y+j][x+3] = clip8(int32(z.ybr[y+j][x+3]) + (a-d)>>3)
47 }
48 }
49
50 func (z *Decoder) inverseDCT4DCOnly(y, x, coeffBase int) {
51 dc := (int32(z.coeff[coeffBase+0]) + 4) >> 3
52 for j := 0; j < 4; j++ {
53 for i := 0; i < 4; i++ {
54 z.ybr[y+j][x+i] = clip8(int32(z.ybr[y+j][x+i]) + dc)
55 }
56 }
57 }
58
59 func (z *Decoder) inverseDCT8(y, x, coeffBase int) {
60 z.inverseDCT4(y+0, x+0, coeffBase+0*16)
61 z.inverseDCT4(y+0, x+4, coeffBase+1*16)
62 z.inverseDCT4(y+4, x+0, coeffBase+2*16)
63 z.inverseDCT4(y+4, x+4, coeffBase+3*16)
64 }
65
66 func (z *Decoder) inverseDCT8DCOnly(y, x, coeffBase int) {
67 z.inverseDCT4DCOnly(y+0, x+0, coeffBase+0*16)
68 z.inverseDCT4DCOnly(y+0, x+4, coeffBase+1*16)
69 z.inverseDCT4DCOnly(y+4, x+0, coeffBase+2*16)
70 z.inverseDCT4DCOnly(y+4, x+4, coeffBase+3*16)
71 }
72
73 func (d *Decoder) inverseWHT16() {
74 var m [16]int32
75 for i := 0; i < 4; i++ {
76 a0 := int32(d.coeff[384+0+i]) + int32(d.coeff[384+12+i])
77 a1 := int32(d.coeff[384+4+i]) + int32(d.coeff[384+8+i])
78 a2 := int32(d.coeff[384+4+i]) - int32(d.coeff[384+8+i])
79 a3 := int32(d.coeff[384+0+i]) - int32(d.coeff[384+12+i])
80 m[0+i] = a0 + a1
81 m[8+i] = a0 - a1
82 m[4+i] = a3 + a2
83 m[12+i] = a3 - a2
84 }
85 out := 0
86 for i := 0; i < 4; i++ {
87 dc := m[0+i*4] + 3
88 a0 := dc + m[3+i*4]
89 a1 := m[1+i*4] + m[2+i*4]
90 a2 := m[1+i*4] - m[2+i*4]
91 a3 := dc - m[3+i*4]
92 d.coeff[out+0] = int16((a0 + a1) >> 3)
93 d.coeff[out+16] = int16((a3 + a2) >> 3)
94 d.coeff[out+32] = int16((a0 - a1) >> 3)
95 d.coeff[out+48] = int16((a3 - a2) >> 3)
96 out += 64
97 }
98 }