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Carla/source/modules/juce_graphics/image_formats/jpglib/jidctflt.c

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  1. /*

  2.  * jidctflt.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 a floating-point implementation of the

  9.  * inverse DCT (Discrete Cosine Transform).  In the IJG code, this routine

  10.  * must also perform dequantization of the input coefficients.

  11.  *

  12.  * This implementation should be more accurate than either of the integer

  13.  * IDCT implementations.  However, it may not give the same results on all

  14.  * machines because of differences in roundoff behavior.  Speed will depend

  15.  * on the hardware's floating point capacity.

  16.  *

  17.  * A 2-D IDCT can be done by 1-D IDCT on each column followed by 1-D IDCT

  18.  * on each row (or vice versa, but it's more convenient to emit a row at

  19.  * a time).  Direct algorithms are also available, but they are much more

  20.  * complex and seem not to be any faster when reduced to code.

  21.  *

  22.  * This implementation is based on Arai, Agui, and Nakajima's algorithm for

  23.  * scaled DCT.  Their original paper (Trans. IEICE E-71(11):1095) is in

  24.  * Japanese, but the algorithm is described in the Pennebaker & Mitchell

  25.  * JPEG textbook (see REFERENCES section in file README).  The following code

  26.  * is based directly on figure 4-8 in P&M.

  27.  * While an 8-point DCT cannot be done in less than 11 multiplies, it is

  28.  * possible to arrange the computation so that many of the multiplies are

  29.  * simple scalings of the final outputs.  These multiplies can then be

  30.  * folded into the multiplications or divisions by the JPEG quantization

  31.  * table entries.  The AA&N method leaves only 5 multiplies and 29 adds

  32.  * to be done in the DCT itself.

  33.  * The primary disadvantage of this method is that with a fixed-point

  34.  * implementation, accuracy is lost due to imprecise representation of the

  35.  * scaled quantization values.  However, that problem does not arise if

  36.  * we use floating point arithmetic.

  37.  */

  38. 

  39. #define JPEG_INTERNALS

  40. #include "jinclude.h"

  41. #include "jpeglib.h"

  42. #include "jdct.h"		/* Private declarations for DCT subsystem */

  43. 

  44. #ifdef DCT_FLOAT_SUPPORTED

  45. 

  46. 

  47. /*

  48.  * This module is specialized to the case DCTSIZE = 8.

  49.  */

  50. 

  51. #if DCTSIZE != 8

  52.   Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */

  53. #endif

  54. 

  55. 

  56. /* Dequantize a coefficient by multiplying it by the multiplier-table

  57.  * entry; produce a float result.

  58.  */

  59. 

  60. #define DEQUANTIZE(coef,quantval)  (((FAST_FLOAT) (coef)) * (quantval))

  61. 

  62. 

  63. /*

  64.  * Perform dequantization and inverse DCT on one block of coefficients.

  65.  */

  66. 

  67. GLOBAL(void)

  68. jpeg_idct_float (j_decompress_ptr cinfo, jpeg_component_info * compptr,

  69. 		 JCOEFPTR coef_block,

  70. 		 JSAMPARRAY output_buf, JDIMENSION output_col)

  71. {

  72.   FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;

  73.   FAST_FLOAT tmp10, tmp11, tmp12, tmp13;

  74.   FAST_FLOAT z5, z10, z11, z12, z13;

  75.   JCOEFPTR inptr;

  76.   FLOAT_MULT_TYPE * quantptr;

  77.   FAST_FLOAT * wsptr;

  78.   JSAMPROW outptr;

  79.   JSAMPLE *range_limit = IDCT_range_limit(cinfo);

  80.   int ctr;

  81.   FAST_FLOAT workspace[DCTSIZE2]; /* buffers data between passes */

  82.   SHIFT_TEMPS

  83. 

  84.   /* Pass 1: process columns from input, store into work array. */

  85. 

  86.   inptr = coef_block;

  87.   quantptr = (FLOAT_MULT_TYPE *) compptr->dct_table;

  88.   wsptr = workspace;

  89.   for (ctr = DCTSIZE; ctr > 0; ctr--) {

  90.     /* Due to quantization, we will usually find that many of the input

  91.      * coefficients are zero, especially the AC terms.  We can exploit this

  92.      * by short-circuiting the IDCT calculation for any column in which all

  93.      * the AC terms are zero.  In that case each output is equal to the

  94.      * DC coefficient (with scale factor as needed).

  95.      * With typical images and quantization tables, half or more of the

  96.      * column DCT calculations can be simplified this way.

  97.      */

  98. 

  99.     if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*2] == 0 &&

  100. 	inptr[DCTSIZE*3] == 0 && inptr[DCTSIZE*4] == 0 &&

  101. 	inptr[DCTSIZE*5] == 0 && inptr[DCTSIZE*6] == 0 &&

  102. 	inptr[DCTSIZE*7] == 0) {

  103.       /* AC terms all zero */

  104.       FAST_FLOAT dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);

  105. 

  106.       wsptr[DCTSIZE*0] = dcval;

  107.       wsptr[DCTSIZE*1] = dcval;

  108.       wsptr[DCTSIZE*2] = dcval;

  109.       wsptr[DCTSIZE*3] = dcval;

  110.       wsptr[DCTSIZE*4] = dcval;

  111.       wsptr[DCTSIZE*5] = dcval;

  112.       wsptr[DCTSIZE*6] = dcval;

  113.       wsptr[DCTSIZE*7] = dcval;

  114. 

  115.       inptr++;			/* advance pointers to next column */

  116.       quantptr++;

  117.       wsptr++;

  118.       continue;

  119.     }

  120. 

  121.     /* Even part */

  122. 

  123.     tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);

  124.     tmp1 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]);

  125.     tmp2 = DEQUANTIZE(inptr[DCTSIZE*4], quantptr[DCTSIZE*4]);

  126.     tmp3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]);

  127. 

  128.     tmp10 = tmp0 + tmp2;	/* phase 3 */

  129.     tmp11 = tmp0 - tmp2;

  130. 

  131.     tmp13 = tmp1 + tmp3;	/* phases 5-3 */

  132.     tmp12 = (tmp1 - tmp3) * ((FAST_FLOAT) 1.414213562) - tmp13; /* 2*c4 */

  133. 

  134.     tmp0 = tmp10 + tmp13;	/* phase 2 */

  135.     tmp3 = tmp10 - tmp13;

  136.     tmp1 = tmp11 + tmp12;

  137.     tmp2 = tmp11 - tmp12;

  138. 

  139.     /* Odd part */

  140. 

  141.     tmp4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);

  142.     tmp5 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);

  143.     tmp6 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);

  144.     tmp7 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);

  145. 

  146.     z13 = tmp6 + tmp5;		/* phase 6 */

  147.     z10 = tmp6 - tmp5;

  148.     z11 = tmp4 + tmp7;

  149.     z12 = tmp4 - tmp7;

  150. 

  151.     tmp7 = z11 + z13;		/* phase 5 */

  152.     tmp11 = (z11 - z13) * ((FAST_FLOAT) 1.414213562); /* 2*c4 */

  153. 

  154.     z5 = (z10 + z12) * ((FAST_FLOAT) 1.847759065); /* 2*c2 */

  155.     tmp10 = ((FAST_FLOAT) 1.082392200) * z12 - z5; /* 2*(c2-c6) */

  156.     tmp12 = ((FAST_FLOAT) -2.613125930) * z10 + z5; /* -2*(c2+c6) */

  157. 

  158.     tmp6 = tmp12 - tmp7;	/* phase 2 */

  159.     tmp5 = tmp11 - tmp6;

  160.     tmp4 = tmp10 + tmp5;

  161. 

  162.     wsptr[DCTSIZE*0] = tmp0 + tmp7;

  163.     wsptr[DCTSIZE*7] = tmp0 - tmp7;

  164.     wsptr[DCTSIZE*1] = tmp1 + tmp6;

  165.     wsptr[DCTSIZE*6] = tmp1 - tmp6;

  166.     wsptr[DCTSIZE*2] = tmp2 + tmp5;

  167.     wsptr[DCTSIZE*5] = tmp2 - tmp5;

  168.     wsptr[DCTSIZE*4] = tmp3 + tmp4;

  169.     wsptr[DCTSIZE*3] = tmp3 - tmp4;

  170. 

  171.     inptr++;			/* advance pointers to next column */

  172.     quantptr++;

  173.     wsptr++;

  174.   }

  175. 

  176.   /* Pass 2: process rows from work array, store into output array. */

  177.   /* Note that we must descale the results by a factor of 8 == 2**3. */

  178. 

  179.   wsptr = workspace;

  180.   for (ctr = 0; ctr < DCTSIZE; ctr++) {

  181.     outptr = output_buf[ctr] + output_col;

  182.     /* Rows of zeroes can be exploited in the same way as we did with columns.

  183.      * However, the column calculation has created many nonzero AC terms, so

  184.      * the simplification applies less often (typically 5% to 10% of the time).

  185.      * And testing floats for zero is relatively expensive, so we don't bother.

  186.      */

  187. 

  188.     /* Even part */

  189. 

  190.     tmp10 = wsptr[0] + wsptr[4];

  191.     tmp11 = wsptr[0] - wsptr[4];

  192. 

  193.     tmp13 = wsptr[2] + wsptr[6];

  194.     tmp12 = (wsptr[2] - wsptr[6]) * ((FAST_FLOAT) 1.414213562) - tmp13;

  195. 

  196.     tmp0 = tmp10 + tmp13;

  197.     tmp3 = tmp10 - tmp13;

  198.     tmp1 = tmp11 + tmp12;

  199.     tmp2 = tmp11 - tmp12;

  200. 

  201.     /* Odd part */

  202. 

  203.     z13 = wsptr[5] + wsptr[3];

  204.     z10 = wsptr[5] - wsptr[3];

  205.     z11 = wsptr[1] + wsptr[7];

  206.     z12 = wsptr[1] - wsptr[7];

  207. 

  208.     tmp7 = z11 + z13;

  209.     tmp11 = (z11 - z13) * ((FAST_FLOAT) 1.414213562);

  210. 

  211.     z5 = (z10 + z12) * ((FAST_FLOAT) 1.847759065); /* 2*c2 */

  212.     tmp10 = ((FAST_FLOAT) 1.082392200) * z12 - z5; /* 2*(c2-c6) */

  213.     tmp12 = ((FAST_FLOAT) -2.613125930) * z10 + z5; /* -2*(c2+c6) */

  214. 

  215.     tmp6 = tmp12 - tmp7;

  216.     tmp5 = tmp11 - tmp6;

  217.     tmp4 = tmp10 + tmp5;

  218. 

  219.     /* Final output stage: scale down by a factor of 8 and range-limit */

  220. 

  221.     outptr[0] = range_limit[(int) DESCALE((INT32) (tmp0 + tmp7), 3)

  222. 			    & RANGE_MASK];

  223.     outptr[7] = range_limit[(int) DESCALE((INT32) (tmp0 - tmp7), 3)

  224. 			    & RANGE_MASK];

  225.     outptr[1] = range_limit[(int) DESCALE((INT32) (tmp1 + tmp6), 3)

  226. 			    & RANGE_MASK];

  227.     outptr[6] = range_limit[(int) DESCALE((INT32) (tmp1 - tmp6), 3)

  228. 			    & RANGE_MASK];

  229.     outptr[2] = range_limit[(int) DESCALE((INT32) (tmp2 + tmp5), 3)

  230. 			    & RANGE_MASK];

  231.     outptr[5] = range_limit[(int) DESCALE((INT32) (tmp2 - tmp5), 3)

  232. 			    & RANGE_MASK];

  233.     outptr[4] = range_limit[(int) DESCALE((INT32) (tmp3 + tmp4), 3)

  234. 			    & RANGE_MASK];

  235.     outptr[3] = range_limit[(int) DESCALE((INT32) (tmp3 - tmp4), 3)

  236. 			    & RANGE_MASK];

  237. 

  238.     wsptr += DCTSIZE;		/* advance pointer to next row */

  239.   }

  240. }

  241. 

  242. #endif /* DCT_FLOAT_SUPPORTED */