mirror of https://github.com/FFmpeg/FFmpeg.git
Originally committed as revision 9604 to svn://svn.ffmpeg.org/ffmpeg/trunkpull/126/head
Ivan Kalvachev
18 years ago
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/* idct.c, inverse fast discrete cosine transform */ |
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/* Copyright (C) 1996, MPEG Software Simulation Group. All Rights Reserved. */ |
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/*
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* Disclaimer of Warranty |
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* |
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* These software programs are available to the user without any license fee or |
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* royalty on an "as is" basis. The MPEG Software Simulation Group disclaims |
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* any and all warranties, whether express, implied, or statuary, including any |
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* implied warranties or merchantability or of fitness for a particular |
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* purpose. In no event shall the copyright-holder be liable for any |
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* incidental, punitive, or consequential damages of any kind whatsoever |
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* arising from the use of these programs. |
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* |
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* This disclaimer of warranty extends to the user of these programs and user's |
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* customers, employees, agents, transferees, successors, and assigns. |
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* |
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* The MPEG Software Simulation Group does not represent or warrant that the |
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* programs furnished hereunder are free of infringement of any third-party |
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* patents. |
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* |
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* Commercial implementations of MPEG-1 and MPEG-2 video, including shareware, |
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* are subject to royalty fees to patent holders. Many of these patents are |
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* general enough such that they are unavoidable regardless of implementation |
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* design. |
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* |
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*/ |
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/**********************************************************/ |
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/* inverse two dimensional DCT, Chen-Wang algorithm */ |
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/* (cf. IEEE ASSP-32, pp. 803-816, Aug. 1984) */ |
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/* 32-bit integer arithmetic (8 bit coefficients) */ |
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/* 11 mults, 29 adds per DCT */ |
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/* sE, 18.8.91 */ |
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/**********************************************************/ |
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/* coefficients extended to 12 bit for IEEE1180-1990 */ |
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/* compliance sE, 2.1.94 */ |
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/**********************************************************/ |
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/* this code assumes >> to be a two's-complement arithmetic */ |
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/* right shift: (-2)>>1 == -1 , (-3)>>1 == -2 */ |
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#define W1 2841 /* 2048*sqrt(2)*cos(1*pi/16) */ |
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#define W2 2676 /* 2048*sqrt(2)*cos(2*pi/16) */ |
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#define W3 2408 /* 2048*sqrt(2)*cos(3*pi/16) */ |
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#define W5 1609 /* 2048*sqrt(2)*cos(5*pi/16) */ |
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#define W6 1108 /* 2048*sqrt(2)*cos(6*pi/16) */ |
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#define W7 565 /* 2048*sqrt(2)*cos(7*pi/16) */ |
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/* row (horizontal) IDCT
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* |
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* 7 pi 1 |
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* dst[k] = sum c[l] * src[l] * cos( -- * ( k + - ) * l ) |
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* l=0 8 2 |
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* |
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* where: c[0] = 128 |
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* c[1..7] = 128*sqrt(2) |
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*/ |
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static void idctrow(blk) |
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short *blk; |
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{ |
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int x0, x1, x2, x3, x4, x5, x6, x7, x8; |
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/* shortcut */ |
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if (!((x1 = blk[4]<<11) | (x2 = blk[6]) | (x3 = blk[2]) | |
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(x4 = blk[1]) | (x5 = blk[7]) | (x6 = blk[5]) | (x7 = blk[3]))) |
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{ |
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blk[0]=blk[1]=blk[2]=blk[3]=blk[4]=blk[5]=blk[6]=blk[7]=blk[0]<<3; |
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return; |
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} |
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x0 = (blk[0]<<11) + 128; /* for proper rounding in the fourth stage */ |
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/* first stage */ |
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x8 = W7*(x4+x5); |
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x4 = x8 + (W1-W7)*x4; |
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x5 = x8 - (W1+W7)*x5; |
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x8 = W3*(x6+x7); |
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x6 = x8 - (W3-W5)*x6; |
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x7 = x8 - (W3+W5)*x7; |
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/* second stage */ |
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x8 = x0 + x1; |
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x0 -= x1; |
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x1 = W6*(x3+x2); |
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x2 = x1 - (W2+W6)*x2; |
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x3 = x1 + (W2-W6)*x3; |
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x1 = x4 + x6; |
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x4 -= x6; |
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x6 = x5 + x7; |
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x5 -= x7; |
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/* third stage */ |
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x7 = x8 + x3; |
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x8 -= x3; |
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x3 = x0 + x2; |
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x0 -= x2; |
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x2 = (181*(x4+x5)+128)>>8; |
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x4 = (181*(x4-x5)+128)>>8; |
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/* fourth stage */ |
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blk[0] = (x7+x1)>>8; |
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blk[1] = (x3+x2)>>8; |
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blk[2] = (x0+x4)>>8; |
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blk[3] = (x8+x6)>>8; |
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blk[4] = (x8-x6)>>8; |
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blk[5] = (x0-x4)>>8; |
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blk[6] = (x3-x2)>>8; |
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blk[7] = (x7-x1)>>8; |
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} |
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/* column (vertical) IDCT
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* |
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* 7 pi 1 |
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* dst[8*k] = sum c[l] * src[8*l] * cos( -- * ( k + - ) * l ) |
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* l=0 8 2 |
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* |
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* where: c[0] = 1/1024 |
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* c[1..7] = (1/1024)*sqrt(2) |
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*/ |
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static void idctcol(blk) |
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short *blk; |
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{ |
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int x0, x1, x2, x3, x4, x5, x6, x7, x8; |
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/* shortcut */ |
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if (!((x1 = (blk[8*4]<<8)) | (x2 = blk[8*6]) | (x3 = blk[8*2]) | |
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(x4 = blk[8*1]) | (x5 = blk[8*7]) | (x6 = blk[8*5]) | (x7 = blk[8*3]))) |
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{ |
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blk[8*0]=blk[8*1]=blk[8*2]=blk[8*3]=blk[8*4]=blk[8*5]=blk[8*6]=blk[8*7]= |
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(blk[8*0]+32)>>6; |
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return; |
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} |
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x0 = (blk[8*0]<<8) + 8192; |
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/* first stage */ |
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x8 = W7*(x4+x5) + 4; |
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x4 = (x8+(W1-W7)*x4)>>3; |
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x5 = (x8-(W1+W7)*x5)>>3; |
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x8 = W3*(x6+x7) + 4; |
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x6 = (x8-(W3-W5)*x6)>>3; |
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x7 = (x8-(W3+W5)*x7)>>3; |
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/* second stage */ |
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x8 = x0 + x1; |
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x0 -= x1; |
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x1 = W6*(x3+x2) + 4; |
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x2 = (x1-(W2+W6)*x2)>>3; |
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x3 = (x1+(W2-W6)*x3)>>3; |
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x1 = x4 + x6; |
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x4 -= x6; |
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x6 = x5 + x7; |
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x5 -= x7; |
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/* third stage */ |
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x7 = x8 + x3; |
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x8 -= x3; |
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x3 = x0 + x2; |
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x0 -= x2; |
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x2 = (181*(x4+x5)+128)>>8; |
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x4 = (181*(x4-x5)+128)>>8; |
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/* fourth stage */ |
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blk[8*0] = (x7+x1)>>14; |
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blk[8*1] = (x3+x2)>>14; |
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blk[8*2] = (x0+x4)>>14; |
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blk[8*3] = (x8+x6)>>14; |
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blk[8*4] = (x8-x6)>>14; |
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blk[8*5] = (x0-x4)>>14; |
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blk[8*6] = (x3-x2)>>14; |
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blk[8*7] = (x7-x1)>>14; |
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} |
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/* two dimensional inverse discrete cosine transform */ |
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void ff_mpeg_idct_c(block) |
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short *block; |
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{ |
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int i; |
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for (i=0; i<8; i++) |
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idctrow(block+8*i); |
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for (i=0; i<8; i++) |
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idctcol(block+i); |
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} |
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