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Diffstat (limited to 'src/pkg/image/jpeg/idct.go')
-rw-r--r-- | src/pkg/image/jpeg/idct.go | 192 |
1 files changed, 0 insertions, 192 deletions
diff --git a/src/pkg/image/jpeg/idct.go b/src/pkg/image/jpeg/idct.go deleted file mode 100644 index 46fcaecb7..000000000 --- a/src/pkg/image/jpeg/idct.go +++ /dev/null @@ -1,192 +0,0 @@ -// Copyright 2009 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 jpeg - -// This is a Go translation of idct.c from -// -// http://standards.iso.org/ittf/PubliclyAvailableStandards/ISO_IEC_13818-4_2004_Conformance_Testing/Video/verifier/mpeg2decode_960109.tar.gz -// -// which carries the following notice: - -/* Copyright (C) 1996, MPEG Software Simulation Group. All Rights Reserved. */ - -/* - * Disclaimer of Warranty - * - * These software programs are available to the user without any license fee or - * royalty on an "as is" basis. The MPEG Software Simulation Group disclaims - * any and all warranties, whether express, implied, or statuary, including any - * implied warranties or merchantability or of fitness for a particular - * purpose. In no event shall the copyright-holder be liable for any - * incidental, punitive, or consequential damages of any kind whatsoever - * arising from the use of these programs. - * - * This disclaimer of warranty extends to the user of these programs and user's - * customers, employees, agents, transferees, successors, and assigns. - * - * The MPEG Software Simulation Group does not represent or warrant that the - * programs furnished hereunder are free of infringement of any third-party - * patents. - * - * Commercial implementations of MPEG-1 and MPEG-2 video, including shareware, - * are subject to royalty fees to patent holders. Many of these patents are - * general enough such that they are unavoidable regardless of implementation - * design. - * - */ - -const blockSize = 64 // A DCT block is 8x8. - -type block [blockSize]int32 - -const ( - w1 = 2841 // 2048*sqrt(2)*cos(1*pi/16) - w2 = 2676 // 2048*sqrt(2)*cos(2*pi/16) - w3 = 2408 // 2048*sqrt(2)*cos(3*pi/16) - w5 = 1609 // 2048*sqrt(2)*cos(5*pi/16) - w6 = 1108 // 2048*sqrt(2)*cos(6*pi/16) - w7 = 565 // 2048*sqrt(2)*cos(7*pi/16) - - w1pw7 = w1 + w7 - w1mw7 = w1 - w7 - w2pw6 = w2 + w6 - w2mw6 = w2 - w6 - w3pw5 = w3 + w5 - w3mw5 = w3 - w5 - - r2 = 181 // 256/sqrt(2) -) - -// idct performs a 2-D Inverse Discrete Cosine Transformation. -// -// The input coefficients should already have been multiplied by the -// appropriate quantization table. We use fixed-point computation, with the -// number of bits for the fractional component varying over the intermediate -// stages. -// -// For more on the actual algorithm, see Z. Wang, "Fast algorithms for the -// discrete W transform and for the discrete Fourier transform", IEEE Trans. on -// ASSP, Vol. ASSP- 32, pp. 803-816, Aug. 1984. -func idct(src *block) { - // Horizontal 1-D IDCT. - for y := 0; y < 8; y++ { - y8 := y * 8 - // If all the AC components are zero, then the IDCT is trivial. - if src[y8+1] == 0 && src[y8+2] == 0 && src[y8+3] == 0 && - src[y8+4] == 0 && src[y8+5] == 0 && src[y8+6] == 0 && src[y8+7] == 0 { - dc := src[y8+0] << 3 - src[y8+0] = dc - src[y8+1] = dc - src[y8+2] = dc - src[y8+3] = dc - src[y8+4] = dc - src[y8+5] = dc - src[y8+6] = dc - src[y8+7] = dc - continue - } - - // Prescale. - x0 := (src[y8+0] << 11) + 128 - x1 := src[y8+4] << 11 - x2 := src[y8+6] - x3 := src[y8+2] - x4 := src[y8+1] - x5 := src[y8+7] - x6 := src[y8+5] - x7 := src[y8+3] - - // Stage 1. - x8 := w7 * (x4 + x5) - x4 = x8 + w1mw7*x4 - x5 = x8 - w1pw7*x5 - x8 = w3 * (x6 + x7) - x6 = x8 - w3mw5*x6 - x7 = x8 - w3pw5*x7 - - // Stage 2. - x8 = x0 + x1 - x0 -= x1 - x1 = w6 * (x3 + x2) - x2 = x1 - w2pw6*x2 - x3 = x1 + w2mw6*x3 - x1 = x4 + x6 - x4 -= x6 - x6 = x5 + x7 - x5 -= x7 - - // Stage 3. - x7 = x8 + x3 - x8 -= x3 - x3 = x0 + x2 - x0 -= x2 - x2 = (r2*(x4+x5) + 128) >> 8 - x4 = (r2*(x4-x5) + 128) >> 8 - - // Stage 4. - src[y8+0] = (x7 + x1) >> 8 - src[y8+1] = (x3 + x2) >> 8 - src[y8+2] = (x0 + x4) >> 8 - src[y8+3] = (x8 + x6) >> 8 - src[y8+4] = (x8 - x6) >> 8 - src[y8+5] = (x0 - x4) >> 8 - src[y8+6] = (x3 - x2) >> 8 - src[y8+7] = (x7 - x1) >> 8 - } - - // Vertical 1-D IDCT. - for x := 0; x < 8; x++ { - // Similar to the horizontal 1-D IDCT case, if all the AC components are zero, then the IDCT is trivial. - // However, after performing the horizontal 1-D IDCT, there are typically non-zero AC components, so - // we do not bother to check for the all-zero case. - - // Prescale. - y0 := (src[8*0+x] << 8) + 8192 - y1 := src[8*4+x] << 8 - y2 := src[8*6+x] - y3 := src[8*2+x] - y4 := src[8*1+x] - y5 := src[8*7+x] - y6 := src[8*5+x] - y7 := src[8*3+x] - - // Stage 1. - y8 := w7*(y4+y5) + 4 - y4 = (y8 + w1mw7*y4) >> 3 - y5 = (y8 - w1pw7*y5) >> 3 - y8 = w3*(y6+y7) + 4 - y6 = (y8 - w3mw5*y6) >> 3 - y7 = (y8 - w3pw5*y7) >> 3 - - // Stage 2. - y8 = y0 + y1 - y0 -= y1 - y1 = w6*(y3+y2) + 4 - y2 = (y1 - w2pw6*y2) >> 3 - y3 = (y1 + w2mw6*y3) >> 3 - y1 = y4 + y6 - y4 -= y6 - y6 = y5 + y7 - y5 -= y7 - - // Stage 3. - y7 = y8 + y3 - y8 -= y3 - y3 = y0 + y2 - y0 -= y2 - y2 = (r2*(y4+y5) + 128) >> 8 - y4 = (r2*(y4-y5) + 128) >> 8 - - // Stage 4. - src[8*0+x] = (y7 + y1) >> 14 - src[8*1+x] = (y3 + y2) >> 14 - src[8*2+x] = (y0 + y4) >> 14 - src[8*3+x] = (y8 + y6) >> 14 - src[8*4+x] = (y8 - y6) >> 14 - src[8*5+x] = (y0 - y4) >> 14 - src[8*6+x] = (y3 - y2) >> 14 - src[8*7+x] = (y7 - y1) >> 14 - } -} |