422 lines
6.2 KiB
C
422 lines
6.2 KiB
C
/* 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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#include "config.h"
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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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/* global declarations */
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void Initialize_Fast_IDCT _ANSI_ARGS_((void));
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void Fast_IDCT _ANSI_ARGS_((short *block));
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/* private data */
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static short iclip[1024]; /* clipping table */
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static short *iclp;
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/* private prototypes */
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static void idctrow _ANSI_ARGS_((short *blk));
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static void idctcol _ANSI_ARGS_((short *blk));
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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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iclp[(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] = iclp[(x7+x1)>>14];
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blk[8*1] = iclp[(x3+x2)>>14];
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blk[8*2] = iclp[(x0+x4)>>14];
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blk[8*3] = iclp[(x8+x6)>>14];
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blk[8*4] = iclp[(x8-x6)>>14];
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blk[8*5] = iclp[(x0-x4)>>14];
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blk[8*6] = iclp[(x3-x2)>>14];
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blk[8*7] = iclp[(x7-x1)>>14];
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}
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/* two dimensional inverse discrete cosine transform */
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void Fast_IDCT(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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void Initialize_Fast_IDCT()
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{
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int i;
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iclp = iclip+512;
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for (i= -512; i<512; i++)
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iclp[i] = (i<-256) ? -256 : ((i>255) ? 255 : i);
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}
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