LCOV - code coverage report
Current view: directory - media/libjpeg - jfdctint.c (source / functions) Found Hit Coverage
Test: app.info Lines: 80 0 0.0 %
Date: 2012-06-02 Functions: 1 0 0.0 %

       1                 : /*
       2                 :  * jfdctint.c
       3                 :  *
       4                 :  * Copyright (C) 1991-1996, Thomas G. Lane.
       5                 :  * This file is part of the Independent JPEG Group's software.
       6                 :  * For conditions of distribution and use, see the accompanying README file.
       7                 :  *
       8                 :  * This file contains a slow-but-accurate integer implementation of the
       9                 :  * forward DCT (Discrete Cosine Transform).
      10                 :  *
      11                 :  * A 2-D DCT can be done by 1-D DCT on each row followed by 1-D DCT
      12                 :  * on each column.  Direct algorithms are also available, but they are
      13                 :  * much more complex and seem not to be any faster when reduced to code.
      14                 :  *
      15                 :  * This implementation is based on an algorithm described in
      16                 :  *   C. Loeffler, A. Ligtenberg and G. Moschytz, "Practical Fast 1-D DCT
      17                 :  *   Algorithms with 11 Multiplications", Proc. Int'l. Conf. on Acoustics,
      18                 :  *   Speech, and Signal Processing 1989 (ICASSP '89), pp. 988-991.
      19                 :  * The primary algorithm described there uses 11 multiplies and 29 adds.
      20                 :  * We use their alternate method with 12 multiplies and 32 adds.
      21                 :  * The advantage of this method is that no data path contains more than one
      22                 :  * multiplication; this allows a very simple and accurate implementation in
      23                 :  * scaled fixed-point arithmetic, with a minimal number of shifts.
      24                 :  */
      25                 : 
      26                 : #define JPEG_INTERNALS
      27                 : #include "jinclude.h"
      28                 : #include "jpeglib.h"
      29                 : #include "jdct.h"             /* Private declarations for DCT subsystem */
      30                 : 
      31                 : #ifdef DCT_ISLOW_SUPPORTED
      32                 : 
      33                 : 
      34                 : /*
      35                 :  * This module is specialized to the case DCTSIZE = 8.
      36                 :  */
      37                 : 
      38                 : #if DCTSIZE != 8
      39                 :   Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
      40                 : #endif
      41                 : 
      42                 : 
      43                 : /*
      44                 :  * The poop on this scaling stuff is as follows:
      45                 :  *
      46                 :  * Each 1-D DCT step produces outputs which are a factor of sqrt(N)
      47                 :  * larger than the true DCT outputs.  The final outputs are therefore
      48                 :  * a factor of N larger than desired; since N=8 this can be cured by
      49                 :  * a simple right shift at the end of the algorithm.  The advantage of
      50                 :  * this arrangement is that we save two multiplications per 1-D DCT,
      51                 :  * because the y0 and y4 outputs need not be divided by sqrt(N).
      52                 :  * In the IJG code, this factor of 8 is removed by the quantization step
      53                 :  * (in jcdctmgr.c), NOT in this module.
      54                 :  *
      55                 :  * We have to do addition and subtraction of the integer inputs, which
      56                 :  * is no problem, and multiplication by fractional constants, which is
      57                 :  * a problem to do in integer arithmetic.  We multiply all the constants
      58                 :  * by CONST_SCALE and convert them to integer constants (thus retaining
      59                 :  * CONST_BITS bits of precision in the constants).  After doing a
      60                 :  * multiplication we have to divide the product by CONST_SCALE, with proper
      61                 :  * rounding, to produce the correct output.  This division can be done
      62                 :  * cheaply as a right shift of CONST_BITS bits.  We postpone shifting
      63                 :  * as long as possible so that partial sums can be added together with
      64                 :  * full fractional precision.
      65                 :  *
      66                 :  * The outputs of the first pass are scaled up by PASS1_BITS bits so that
      67                 :  * they are represented to better-than-integral precision.  These outputs
      68                 :  * require BITS_IN_JSAMPLE + PASS1_BITS + 3 bits; this fits in a 16-bit word
      69                 :  * with the recommended scaling.  (For 12-bit sample data, the intermediate
      70                 :  * array is INT32 anyway.)
      71                 :  *
      72                 :  * To avoid overflow of the 32-bit intermediate results in pass 2, we must
      73                 :  * have BITS_IN_JSAMPLE + CONST_BITS + PASS1_BITS <= 26.  Error analysis
      74                 :  * shows that the values given below are the most effective.
      75                 :  */
      76                 : 
      77                 : #if BITS_IN_JSAMPLE == 8
      78                 : #define CONST_BITS  13
      79                 : #define PASS1_BITS  2
      80                 : #else
      81                 : #define CONST_BITS  13
      82                 : #define PASS1_BITS  1           /* lose a little precision to avoid overflow */
      83                 : #endif
      84                 : 
      85                 : /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
      86                 :  * causing a lot of useless floating-point operations at run time.
      87                 :  * To get around this we use the following pre-calculated constants.
      88                 :  * If you change CONST_BITS you may want to add appropriate values.
      89                 :  * (With a reasonable C compiler, you can just rely on the FIX() macro...)
      90                 :  */
      91                 : 
      92                 : #if CONST_BITS == 13
      93                 : #define FIX_0_298631336  ((INT32)  2446)        /* FIX(0.298631336) */
      94                 : #define FIX_0_390180644  ((INT32)  3196)        /* FIX(0.390180644) */
      95                 : #define FIX_0_541196100  ((INT32)  4433)        /* FIX(0.541196100) */
      96                 : #define FIX_0_765366865  ((INT32)  6270)        /* FIX(0.765366865) */
      97                 : #define FIX_0_899976223  ((INT32)  7373)        /* FIX(0.899976223) */
      98                 : #define FIX_1_175875602  ((INT32)  9633)        /* FIX(1.175875602) */
      99                 : #define FIX_1_501321110  ((INT32)  12299)       /* FIX(1.501321110) */
     100                 : #define FIX_1_847759065  ((INT32)  15137)       /* FIX(1.847759065) */
     101                 : #define FIX_1_961570560  ((INT32)  16069)       /* FIX(1.961570560) */
     102                 : #define FIX_2_053119869  ((INT32)  16819)       /* FIX(2.053119869) */
     103                 : #define FIX_2_562915447  ((INT32)  20995)       /* FIX(2.562915447) */
     104                 : #define FIX_3_072711026  ((INT32)  25172)       /* FIX(3.072711026) */
     105                 : #else
     106                 : #define FIX_0_298631336  FIX(0.298631336)
     107                 : #define FIX_0_390180644  FIX(0.390180644)
     108                 : #define FIX_0_541196100  FIX(0.541196100)
     109                 : #define FIX_0_765366865  FIX(0.765366865)
     110                 : #define FIX_0_899976223  FIX(0.899976223)
     111                 : #define FIX_1_175875602  FIX(1.175875602)
     112                 : #define FIX_1_501321110  FIX(1.501321110)
     113                 : #define FIX_1_847759065  FIX(1.847759065)
     114                 : #define FIX_1_961570560  FIX(1.961570560)
     115                 : #define FIX_2_053119869  FIX(2.053119869)
     116                 : #define FIX_2_562915447  FIX(2.562915447)
     117                 : #define FIX_3_072711026  FIX(3.072711026)
     118                 : #endif
     119                 : 
     120                 : 
     121                 : /* Multiply an INT32 variable by an INT32 constant to yield an INT32 result.
     122                 :  * For 8-bit samples with the recommended scaling, all the variable
     123                 :  * and constant values involved are no more than 16 bits wide, so a
     124                 :  * 16x16->32 bit multiply can be used instead of a full 32x32 multiply.
     125                 :  * For 12-bit samples, a full 32-bit multiplication will be needed.
     126                 :  */
     127                 : 
     128                 : #if BITS_IN_JSAMPLE == 8
     129                 : #define MULTIPLY(var,const)  MULTIPLY16C16(var,const)
     130                 : #else
     131                 : #define MULTIPLY(var,const)  ((var) * (const))
     132                 : #endif
     133                 : 
     134                 : 
     135                 : /*
     136                 :  * Perform the forward DCT on one block of samples.
     137                 :  */
     138                 : 
     139                 : GLOBAL(void)
     140               0 : jpeg_fdct_islow (DCTELEM * data)
     141                 : {
     142                 :   INT32 tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
     143                 :   INT32 tmp10, tmp11, tmp12, tmp13;
     144                 :   INT32 z1, z2, z3, z4, z5;
     145                 :   DCTELEM *dataptr;
     146                 :   int ctr;
     147                 :   SHIFT_TEMPS
     148                 : 
     149                 :   /* Pass 1: process rows. */
     150                 :   /* Note results are scaled up by sqrt(8) compared to a true DCT; */
     151                 :   /* furthermore, we scale the results by 2**PASS1_BITS. */
     152                 : 
     153               0 :   dataptr = data;
     154               0 :   for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
     155               0 :     tmp0 = dataptr[0] + dataptr[7];
     156               0 :     tmp7 = dataptr[0] - dataptr[7];
     157               0 :     tmp1 = dataptr[1] + dataptr[6];
     158               0 :     tmp6 = dataptr[1] - dataptr[6];
     159               0 :     tmp2 = dataptr[2] + dataptr[5];
     160               0 :     tmp5 = dataptr[2] - dataptr[5];
     161               0 :     tmp3 = dataptr[3] + dataptr[4];
     162               0 :     tmp4 = dataptr[3] - dataptr[4];
     163                 :     
     164                 :     /* Even part per LL&M figure 1 --- note that published figure is faulty;
     165                 :      * rotator "sqrt(2)*c1" should be "sqrt(2)*c6".
     166                 :      */
     167                 :     
     168               0 :     tmp10 = tmp0 + tmp3;
     169               0 :     tmp13 = tmp0 - tmp3;
     170               0 :     tmp11 = tmp1 + tmp2;
     171               0 :     tmp12 = tmp1 - tmp2;
     172                 :     
     173               0 :     dataptr[0] = (DCTELEM) ((tmp10 + tmp11) << PASS1_BITS);
     174               0 :     dataptr[4] = (DCTELEM) ((tmp10 - tmp11) << PASS1_BITS);
     175                 :     
     176               0 :     z1 = MULTIPLY(tmp12 + tmp13, FIX_0_541196100);
     177               0 :     dataptr[2] = (DCTELEM) DESCALE(z1 + MULTIPLY(tmp13, FIX_0_765366865),
     178                 :                                    CONST_BITS-PASS1_BITS);
     179               0 :     dataptr[6] = (DCTELEM) DESCALE(z1 + MULTIPLY(tmp12, - FIX_1_847759065),
     180                 :                                    CONST_BITS-PASS1_BITS);
     181                 :     
     182                 :     /* Odd part per figure 8 --- note paper omits factor of sqrt(2).
     183                 :      * cK represents cos(K*pi/16).
     184                 :      * i0..i3 in the paper are tmp4..tmp7 here.
     185                 :      */
     186                 :     
     187               0 :     z1 = tmp4 + tmp7;
     188               0 :     z2 = tmp5 + tmp6;
     189               0 :     z3 = tmp4 + tmp6;
     190               0 :     z4 = tmp5 + tmp7;
     191               0 :     z5 = MULTIPLY(z3 + z4, FIX_1_175875602); /* sqrt(2) * c3 */
     192                 :     
     193               0 :     tmp4 = MULTIPLY(tmp4, FIX_0_298631336); /* sqrt(2) * (-c1+c3+c5-c7) */
     194               0 :     tmp5 = MULTIPLY(tmp5, FIX_2_053119869); /* sqrt(2) * ( c1+c3-c5+c7) */
     195               0 :     tmp6 = MULTIPLY(tmp6, FIX_3_072711026); /* sqrt(2) * ( c1+c3+c5-c7) */
     196               0 :     tmp7 = MULTIPLY(tmp7, FIX_1_501321110); /* sqrt(2) * ( c1+c3-c5-c7) */
     197               0 :     z1 = MULTIPLY(z1, - FIX_0_899976223); /* sqrt(2) * (c7-c3) */
     198               0 :     z2 = MULTIPLY(z2, - FIX_2_562915447); /* sqrt(2) * (-c1-c3) */
     199               0 :     z3 = MULTIPLY(z3, - FIX_1_961570560); /* sqrt(2) * (-c3-c5) */
     200               0 :     z4 = MULTIPLY(z4, - FIX_0_390180644); /* sqrt(2) * (c5-c3) */
     201                 :     
     202               0 :     z3 += z5;
     203               0 :     z4 += z5;
     204                 :     
     205               0 :     dataptr[7] = (DCTELEM) DESCALE(tmp4 + z1 + z3, CONST_BITS-PASS1_BITS);
     206               0 :     dataptr[5] = (DCTELEM) DESCALE(tmp5 + z2 + z4, CONST_BITS-PASS1_BITS);
     207               0 :     dataptr[3] = (DCTELEM) DESCALE(tmp6 + z2 + z3, CONST_BITS-PASS1_BITS);
     208               0 :     dataptr[1] = (DCTELEM) DESCALE(tmp7 + z1 + z4, CONST_BITS-PASS1_BITS);
     209                 :     
     210               0 :     dataptr += DCTSIZE;         /* advance pointer to next row */
     211                 :   }
     212                 : 
     213                 :   /* Pass 2: process columns.
     214                 :    * We remove the PASS1_BITS scaling, but leave the results scaled up
     215                 :    * by an overall factor of 8.
     216                 :    */
     217                 : 
     218               0 :   dataptr = data;
     219               0 :   for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
     220               0 :     tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7];
     221               0 :     tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7];
     222               0 :     tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6];
     223               0 :     tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6];
     224               0 :     tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5];
     225               0 :     tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5];
     226               0 :     tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4];
     227               0 :     tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4];
     228                 :     
     229                 :     /* Even part per LL&M figure 1 --- note that published figure is faulty;
     230                 :      * rotator "sqrt(2)*c1" should be "sqrt(2)*c6".
     231                 :      */
     232                 :     
     233               0 :     tmp10 = tmp0 + tmp3;
     234               0 :     tmp13 = tmp0 - tmp3;
     235               0 :     tmp11 = tmp1 + tmp2;
     236               0 :     tmp12 = tmp1 - tmp2;
     237                 :     
     238               0 :     dataptr[DCTSIZE*0] = (DCTELEM) DESCALE(tmp10 + tmp11, PASS1_BITS);
     239               0 :     dataptr[DCTSIZE*4] = (DCTELEM) DESCALE(tmp10 - tmp11, PASS1_BITS);
     240                 :     
     241               0 :     z1 = MULTIPLY(tmp12 + tmp13, FIX_0_541196100);
     242               0 :     dataptr[DCTSIZE*2] = (DCTELEM) DESCALE(z1 + MULTIPLY(tmp13, FIX_0_765366865),
     243                 :                                            CONST_BITS+PASS1_BITS);
     244               0 :     dataptr[DCTSIZE*6] = (DCTELEM) DESCALE(z1 + MULTIPLY(tmp12, - FIX_1_847759065),
     245                 :                                            CONST_BITS+PASS1_BITS);
     246                 :     
     247                 :     /* Odd part per figure 8 --- note paper omits factor of sqrt(2).
     248                 :      * cK represents cos(K*pi/16).
     249                 :      * i0..i3 in the paper are tmp4..tmp7 here.
     250                 :      */
     251                 :     
     252               0 :     z1 = tmp4 + tmp7;
     253               0 :     z2 = tmp5 + tmp6;
     254               0 :     z3 = tmp4 + tmp6;
     255               0 :     z4 = tmp5 + tmp7;
     256               0 :     z5 = MULTIPLY(z3 + z4, FIX_1_175875602); /* sqrt(2) * c3 */
     257                 :     
     258               0 :     tmp4 = MULTIPLY(tmp4, FIX_0_298631336); /* sqrt(2) * (-c1+c3+c5-c7) */
     259               0 :     tmp5 = MULTIPLY(tmp5, FIX_2_053119869); /* sqrt(2) * ( c1+c3-c5+c7) */
     260               0 :     tmp6 = MULTIPLY(tmp6, FIX_3_072711026); /* sqrt(2) * ( c1+c3+c5-c7) */
     261               0 :     tmp7 = MULTIPLY(tmp7, FIX_1_501321110); /* sqrt(2) * ( c1+c3-c5-c7) */
     262               0 :     z1 = MULTIPLY(z1, - FIX_0_899976223); /* sqrt(2) * (c7-c3) */
     263               0 :     z2 = MULTIPLY(z2, - FIX_2_562915447); /* sqrt(2) * (-c1-c3) */
     264               0 :     z3 = MULTIPLY(z3, - FIX_1_961570560); /* sqrt(2) * (-c3-c5) */
     265               0 :     z4 = MULTIPLY(z4, - FIX_0_390180644); /* sqrt(2) * (c5-c3) */
     266                 :     
     267               0 :     z3 += z5;
     268               0 :     z4 += z5;
     269                 :     
     270               0 :     dataptr[DCTSIZE*7] = (DCTELEM) DESCALE(tmp4 + z1 + z3,
     271                 :                                            CONST_BITS+PASS1_BITS);
     272               0 :     dataptr[DCTSIZE*5] = (DCTELEM) DESCALE(tmp5 + z2 + z4,
     273                 :                                            CONST_BITS+PASS1_BITS);
     274               0 :     dataptr[DCTSIZE*3] = (DCTELEM) DESCALE(tmp6 + z2 + z3,
     275                 :                                            CONST_BITS+PASS1_BITS);
     276               0 :     dataptr[DCTSIZE*1] = (DCTELEM) DESCALE(tmp7 + z1 + z4,
     277                 :                                            CONST_BITS+PASS1_BITS);
     278                 :     
     279               0 :     dataptr++;                  /* advance pointer to next column */
     280                 :   }
     281               0 : }
     282                 : 
     283                 : #endif /* DCT_ISLOW_SUPPORTED */

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