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 // 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 } }