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  1. /*
  2.  * jidctred.c
  3.  *
  4.  * Copyright (C) 1994-1998, 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 inverse-DCT routines that produce reduced-size output:
  9.  * either 4x4, 2x2, or 1x1 pixels from an 8x8 DCT block.
  10.  *
  11.  * The implementation is based on the Loeffler, Ligtenberg and Moschytz (LL&M)
  12.  * algorithm used in jidctint.c.  We simply replace each 8-to-8 1-D IDCT step
  13.  * with an 8-to-4 step that produces the four averages of two adjacent outputs
  14.  * (or an 8-to-2 step producing two averages of four outputs, for 2x2 output).
  15.  * These steps were derived by computing the corresponding values at the end
  16.  * of the normal LL&M code, then simplifying as much as possible.
  17.  *
  18.  * 1x1 is trivial: just take the DC coefficient divided by 8.
  19.  *
  20.  * See jidctint.c for additional comments.
  21.  */
  22.  
  23. #define JPEG_INTERNALS
  24. #include "jinclude.h"
  25. #include "jpeglib.h"
  26. #include "jdct.h"               /* Private declarations for DCT subsystem */
  27.  
  28. #ifdef IDCT_SCALING_SUPPORTED
  29.  
  30.  
  31. /*
  32.  * This module is specialized to the case DCTSIZE = 8.
  33.  */
  34.  
  35. #if DCTSIZE != 8
  36.   Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
  37. #endif
  38.  
  39.  
  40. /* Scaling is the same as in jidctint.c. */
  41.  
  42. #if BITS_IN_JSAMPLE == 8
  43. #define CONST_BITS  13
  44. #define PASS1_BITS  2
  45. #else
  46. #define CONST_BITS  13
  47. #define PASS1_BITS  1           /* lose a little precision to avoid overflow */
  48. #endif
  49.  
  50. /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
  51.  * causing a lot of useless floating-point operations at run time.
  52.  * To get around this we use the following pre-calculated constants.
  53.  * If you change CONST_BITS you may want to add appropriate values.
  54.  * (With a reasonable C compiler, you can just rely on the FIX() macro...)
  55.  */
  56.  
  57. #if CONST_BITS == 13
  58. #define FIX_0_211164243  ((INT32)  1730)        /* FIX(0.211164243) */
  59. #define FIX_0_509795579  ((INT32)  4176)        /* FIX(0.509795579) */
  60. #define FIX_0_601344887  ((INT32)  4926)        /* FIX(0.601344887) */
  61. #define FIX_0_720959822  ((INT32)  5906)        /* FIX(0.720959822) */
  62. #define FIX_0_765366865  ((INT32)  6270)        /* FIX(0.765366865) */
  63. #define FIX_0_850430095  ((INT32)  6967)        /* FIX(0.850430095) */
  64. #define FIX_0_899976223  ((INT32)  7373)        /* FIX(0.899976223) */
  65. #define FIX_1_061594337  ((INT32)  8697)        /* FIX(1.061594337) */
  66. #define FIX_1_272758580  ((INT32)  10426)       /* FIX(1.272758580) */
  67. #define FIX_1_451774981  ((INT32)  11893)       /* FIX(1.451774981) */
  68. #define FIX_1_847759065  ((INT32)  15137)       /* FIX(1.847759065) */
  69. #define FIX_2_172734803  ((INT32)  17799)       /* FIX(2.172734803) */
  70. #define FIX_2_562915447  ((INT32)  20995)       /* FIX(2.562915447) */
  71. #define FIX_3_624509785  ((INT32)  29692)       /* FIX(3.624509785) */
  72. #else
  73. #define FIX_0_211164243  FIX(0.211164243)
  74. #define FIX_0_509795579  FIX(0.509795579)
  75. #define FIX_0_601344887  FIX(0.601344887)
  76. #define FIX_0_720959822  FIX(0.720959822)
  77. #define FIX_0_765366865  FIX(0.765366865)
  78. #define FIX_0_850430095  FIX(0.850430095)
  79. #define FIX_0_899976223  FIX(0.899976223)
  80. #define FIX_1_061594337  FIX(1.061594337)
  81. #define FIX_1_272758580  FIX(1.272758580)
  82. #define FIX_1_451774981  FIX(1.451774981)
  83. #define FIX_1_847759065  FIX(1.847759065)
  84. #define FIX_2_172734803  FIX(2.172734803)
  85. #define FIX_2_562915447  FIX(2.562915447)
  86. #define FIX_3_624509785  FIX(3.624509785)
  87. #endif
  88.  
  89.  
  90. /* Multiply an INT32 variable by an INT32 constant to yield an INT32 result.
  91.  * For 8-bit samples with the recommended scaling, all the variable
  92.  * and constant values involved are no more than 16 bits wide, so a
  93.  * 16x16->32 bit multiply can be used instead of a full 32x32 multiply.
  94.  * For 12-bit samples, a full 32-bit multiplication will be needed.
  95.  */
  96.  
  97. #if BITS_IN_JSAMPLE == 8
  98. #define MULTIPLY(var,const)  MULTIPLY16C16(var,const)
  99. #else
  100. #define MULTIPLY(var,const)  ((var) * (const))
  101. #endif
  102.  
  103.  
  104. /* Dequantize a coefficient by multiplying it by the multiplier-table
  105.  * entry; produce an int result.  In this module, both inputs and result
  106.  * are 16 bits or less, so either int or short multiply will work.
  107.  */
  108.  
  109. #define DEQUANTIZE(coef,quantval)  (((ISLOW_MULT_TYPE) (coef)) * (quantval))
  110.  
  111.  
  112. /*
  113.  * Perform dequantization and inverse DCT on one block of coefficients,
  114.  * producing a reduced-size 4x4 output block.
  115.  */
  116.  
  117. GLOBAL(void)
  118. jpeg_idct_4x4 (j_decompress_ptr cinfo, jpeg_component_info * compptr,
  119.                JCOEFPTR coef_block,
  120.                JSAMPARRAY output_buf, JDIMENSION output_col)
  121. {
  122.   INT32 tmp0, tmp2, tmp10, tmp12;
  123.   INT32 z1, z2, z3, z4;
  124.   JCOEFPTR inptr;
  125.   ISLOW_MULT_TYPE * quantptr;
  126.   int * wsptr;
  127.   JSAMPROW outptr;
  128.   JSAMPLE *range_limit = IDCT_range_limit(cinfo);
  129.   int ctr;
  130.   int workspace[DCTSIZE*4];     /* buffers data between passes */
  131.   SHIFT_TEMPS
  132.  
  133.   /* Pass 1: process columns from input, store into work array. */
  134.  
  135.   inptr = coef_block;
  136.   quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
  137.   wsptr = workspace;
  138.   for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) {
  139.     /* Don't bother to process column 4, because second pass won't use it */
  140.     if (ctr == DCTSIZE-4)
  141.       continue;
  142.     if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*2] == 0 &&
  143.         inptr[DCTSIZE*3] == 0 && inptr[DCTSIZE*5] == 0 &&
  144.         inptr[DCTSIZE*6] == 0 && inptr[DCTSIZE*7] == 0) {
  145.       /* AC terms all zero; we need not examine term 4 for 4x4 output */
  146.       int dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]) << PASS1_BITS;
  147.      
  148.       wsptr[DCTSIZE*0] = dcval;
  149.       wsptr[DCTSIZE*1] = dcval;
  150.       wsptr[DCTSIZE*2] = dcval;
  151.       wsptr[DCTSIZE*3] = dcval;
  152.      
  153.       continue;
  154.     }
  155.    
  156.     /* Even part */
  157.    
  158.     tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
  159.     tmp0 <<= (CONST_BITS+1);
  160.    
  161.     z2 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]);
  162.     z3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]);
  163.  
  164.     tmp2 = MULTIPLY(z2, FIX_1_847759065) + MULTIPLY(z3, - FIX_0_765366865);
  165.    
  166.     tmp10 = tmp0 + tmp2;
  167.     tmp12 = tmp0 - tmp2;
  168.    
  169.     /* Odd part */
  170.    
  171.     z1 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
  172.     z2 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
  173.     z3 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
  174.     z4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
  175.    
  176.     tmp0 = MULTIPLY(z1, - FIX_0_211164243) /* sqrt(2) * (c3-c1) */
  177.          + MULTIPLY(z2, FIX_1_451774981) /* sqrt(2) * (c3+c7) */
  178.          + MULTIPLY(z3, - FIX_2_172734803) /* sqrt(2) * (-c1-c5) */
  179.          + MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * (c5+c7) */
  180.    
  181.     tmp2 = MULTIPLY(z1, - FIX_0_509795579) /* sqrt(2) * (c7-c5) */
  182.          + MULTIPLY(z2, - FIX_0_601344887) /* sqrt(2) * (c5-c1) */
  183.          + MULTIPLY(z3, FIX_0_899976223) /* sqrt(2) * (c3-c7) */
  184.          + MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */
  185.  
  186.     /* Final output stage */
  187.    
  188.     wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp2, CONST_BITS-PASS1_BITS+1);
  189.     wsptr[DCTSIZE*3] = (int) DESCALE(tmp10 - tmp2, CONST_BITS-PASS1_BITS+1);
  190.     wsptr[DCTSIZE*1] = (int) DESCALE(tmp12 + tmp0, CONST_BITS-PASS1_BITS+1);
  191.     wsptr[DCTSIZE*2] = (int) DESCALE(tmp12 - tmp0, CONST_BITS-PASS1_BITS+1);
  192.   }
  193.  
  194.   /* Pass 2: process 4 rows from work array, store into output array. */
  195.  
  196.   wsptr = workspace;
  197.   for (ctr = 0; ctr < 4; ctr++) {
  198.     outptr = output_buf[ctr] + output_col;
  199.     /* It's not clear whether a zero row test is worthwhile here ... */
  200.  
  201. #ifndef NO_ZERO_ROW_TEST
  202.     if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 &&
  203.         wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) {
  204.       /* AC terms all zero */
  205.       JSAMPLE dcval = range_limit[(int) DESCALE((INT32) wsptr[0], PASS1_BITS+3)
  206.                                   & RANGE_MASK];
  207.      
  208.       outptr[0] = dcval;
  209.       outptr[1] = dcval;
  210.       outptr[2] = dcval;
  211.       outptr[3] = dcval;
  212.      
  213.       wsptr += DCTSIZE;         /* advance pointer to next row */
  214.       continue;
  215.     }
  216. #endif
  217.    
  218.     /* Even part */
  219.    
  220.     tmp0 = ((INT32) wsptr[0]) << (CONST_BITS+1);
  221.    
  222.     tmp2 = MULTIPLY((INT32) wsptr[2], FIX_1_847759065)
  223.          + MULTIPLY((INT32) wsptr[6], - FIX_0_765366865);
  224.    
  225.     tmp10 = tmp0 + tmp2;
  226.     tmp12 = tmp0 - tmp2;
  227.    
  228.     /* Odd part */
  229.    
  230.     z1 = (INT32) wsptr[7];
  231.     z2 = (INT32) wsptr[5];
  232.     z3 = (INT32) wsptr[3];
  233.     z4 = (INT32) wsptr[1];
  234.    
  235.     tmp0 = MULTIPLY(z1, - FIX_0_211164243) /* sqrt(2) * (c3-c1) */
  236.          + MULTIPLY(z2, FIX_1_451774981) /* sqrt(2) * (c3+c7) */
  237.          + MULTIPLY(z3, - FIX_2_172734803) /* sqrt(2) * (-c1-c5) */
  238.          + MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * (c5+c7) */
  239.    
  240.     tmp2 = MULTIPLY(z1, - FIX_0_509795579) /* sqrt(2) * (c7-c5) */
  241.          + MULTIPLY(z2, - FIX_0_601344887) /* sqrt(2) * (c5-c1) */
  242.          + MULTIPLY(z3, FIX_0_899976223) /* sqrt(2) * (c3-c7) */
  243.          + MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */
  244.  
  245.     /* Final output stage */
  246.    
  247.     outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp2,
  248.                                           CONST_BITS+PASS1_BITS+3+1)
  249.                             & RANGE_MASK];
  250.     outptr[3] = range_limit[(int) DESCALE(tmp10 - tmp2,
  251.                                           CONST_BITS+PASS1_BITS+3+1)
  252.                             & RANGE_MASK];
  253.     outptr[1] = range_limit[(int) DESCALE(tmp12 + tmp0,
  254.                                           CONST_BITS+PASS1_BITS+3+1)
  255.                             & RANGE_MASK];
  256.     outptr[2] = range_limit[(int) DESCALE(tmp12 - tmp0,
  257.                                           CONST_BITS+PASS1_BITS+3+1)
  258.                             & RANGE_MASK];
  259.    
  260.     wsptr += DCTSIZE;           /* advance pointer to next row */
  261.   }
  262. }
  263.  
  264.  
  265. /*
  266.  * Perform dequantization and inverse DCT on one block of coefficients,
  267.  * producing a reduced-size 2x2 output block.
  268.  */
  269.  
  270. GLOBAL(void)
  271. jpeg_idct_2x2 (j_decompress_ptr cinfo, jpeg_component_info * compptr,
  272.                JCOEFPTR coef_block,
  273.                JSAMPARRAY output_buf, JDIMENSION output_col)
  274. {
  275.   INT32 tmp0, tmp10, z1;
  276.   JCOEFPTR inptr;
  277.   ISLOW_MULT_TYPE * quantptr;
  278.   int * wsptr;
  279.   JSAMPROW outptr;
  280.   JSAMPLE *range_limit = IDCT_range_limit(cinfo);
  281.   int ctr;
  282.   int workspace[DCTSIZE*2];     /* buffers data between passes */
  283.   SHIFT_TEMPS
  284.  
  285.   /* Pass 1: process columns from input, store into work array. */
  286.  
  287.   inptr = coef_block;
  288.   quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
  289.   wsptr = workspace;
  290.   for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) {
  291.     /* Don't bother to process columns 2,4,6 */
  292.     if (ctr == DCTSIZE-2 || ctr == DCTSIZE-4 || ctr == DCTSIZE-6)
  293.       continue;
  294.     if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*3] == 0 &&
  295.         inptr[DCTSIZE*5] == 0 && inptr[DCTSIZE*7] == 0) {
  296.       /* AC terms all zero; we need not examine terms 2,4,6 for 2x2 output */
  297.       int dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]) << PASS1_BITS;
  298.      
  299.       wsptr[DCTSIZE*0] = dcval;
  300.       wsptr[DCTSIZE*1] = dcval;
  301.      
  302.       continue;
  303.     }
  304.    
  305.     /* Even part */
  306.    
  307.     z1 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
  308.     tmp10 = z1 << (CONST_BITS+2);
  309.    
  310.     /* Odd part */
  311.  
  312.     z1 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
  313.     tmp0 = MULTIPLY(z1, - FIX_0_720959822); /* sqrt(2) * (c7-c5+c3-c1) */
  314.     z1 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
  315.     tmp0 += MULTIPLY(z1, FIX_0_850430095); /* sqrt(2) * (-c1+c3+c5+c7) */
  316.     z1 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
  317.     tmp0 += MULTIPLY(z1, - FIX_1_272758580); /* sqrt(2) * (-c1+c3-c5-c7) */
  318.     z1 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
  319.     tmp0 += MULTIPLY(z1, FIX_3_624509785); /* sqrt(2) * (c1+c3+c5+c7) */
  320.  
  321.     /* Final output stage */
  322.    
  323.     wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp0, CONST_BITS-PASS1_BITS+2);
  324.     wsptr[DCTSIZE*1] = (int) DESCALE(tmp10 - tmp0, CONST_BITS-PASS1_BITS+2);
  325.   }
  326.  
  327.   /* Pass 2: process 2 rows from work array, store into output array. */
  328.  
  329.   wsptr = workspace;
  330.   for (ctr = 0; ctr < 2; ctr++) {
  331.     outptr = output_buf[ctr] + output_col;
  332.     /* It's not clear whether a zero row test is worthwhile here ... */
  333.  
  334. #ifndef NO_ZERO_ROW_TEST
  335.     if (wsptr[1] == 0 && wsptr[3] == 0 && wsptr[5] == 0 && wsptr[7] == 0) {
  336.       /* AC terms all zero */
  337.       JSAMPLE dcval = range_limit[(int) DESCALE((INT32) wsptr[0], PASS1_BITS+3)
  338.                                   & RANGE_MASK];
  339.      
  340.       outptr[0] = dcval;
  341.       outptr[1] = dcval;
  342.      
  343.       wsptr += DCTSIZE;         /* advance pointer to next row */
  344.       continue;
  345.     }
  346. #endif
  347.    
  348.     /* Even part */
  349.    
  350.     tmp10 = ((INT32) wsptr[0]) << (CONST_BITS+2);
  351.    
  352.     /* Odd part */
  353.  
  354.     tmp0 = MULTIPLY((INT32) wsptr[7], - FIX_0_720959822) /* sqrt(2) * (c7-c5+c3-c1) */
  355.          + MULTIPLY((INT32) wsptr[5], FIX_0_850430095) /* sqrt(2) * (-c1+c3+c5+c7) */
  356.          + MULTIPLY((INT32) wsptr[3], - FIX_1_272758580) /* sqrt(2) * (-c1+c3-c5-c7) */
  357.          + MULTIPLY((INT32) wsptr[1], FIX_3_624509785); /* sqrt(2) * (c1+c3+c5+c7) */
  358.  
  359.     /* Final output stage */
  360.    
  361.     outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp0,
  362.                                           CONST_BITS+PASS1_BITS+3+2)
  363.                             & RANGE_MASK];
  364.     outptr[1] = range_limit[(int) DESCALE(tmp10 - tmp0,
  365.                                           CONST_BITS+PASS1_BITS+3+2)
  366.                             & RANGE_MASK];
  367.    
  368.     wsptr += DCTSIZE;           /* advance pointer to next row */
  369.   }
  370. }
  371.  
  372.  
  373. /*
  374.  * Perform dequantization and inverse DCT on one block of coefficients,
  375.  * producing a reduced-size 1x1 output block.
  376.  */
  377.  
  378. GLOBAL(void)
  379. jpeg_idct_1x1 (j_decompress_ptr cinfo, jpeg_component_info * compptr,
  380.                JCOEFPTR coef_block,
  381.                JSAMPARRAY output_buf, JDIMENSION output_col)
  382. {
  383.   int dcval;
  384.   ISLOW_MULT_TYPE * quantptr;
  385.   JSAMPLE *range_limit = IDCT_range_limit(cinfo);
  386.   SHIFT_TEMPS
  387.  
  388.   /* We hardly need an inverse DCT routine for this: just take the
  389.    * average pixel value, which is one-eighth of the DC coefficient.
  390.    */
  391.   quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
  392.   dcval = DEQUANTIZE(coef_block[0], quantptr[0]);
  393.   dcval = (int) DESCALE((INT32) dcval, 3);
  394.  
  395.   output_buf[0][output_col] = range_limit[dcval & RANGE_MASK];
  396. }
  397.  
  398. #endif /* IDCT_SCALING_SUPPORTED */
  399.