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ntk/jpeg/jidctfst.c

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  1. /*

  2.  * jidctfst.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 fast, not so accurate integer 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.  * A 2-D IDCT can be done by 1-D IDCT on each column followed by 1-D IDCT

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

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

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

  16.  *

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

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

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

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

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

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

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

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

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

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

  27.  * to be done in the DCT itself.

  28.  * The primary disadvantage of this method is that with fixed-point math,

  29.  * accuracy is lost due to imprecise representation of the scaled

  30.  * quantization values.  The smaller the quantization table entry, the less

  31.  * precise the scaled value, so this implementation does worse with high-

  32.  * quality-setting files than with low-quality ones.

  33.  */

  34. 

  35. #define JPEG_INTERNALS

  36. #include "jinclude.h"

  37. #include "jpeglib.h"

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

  39. 

  40. #ifdef DCT_IFAST_SUPPORTED

  41. 

  42. 

  43. /*

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

  45.  */

  46. 

  47. #if DCTSIZE != 8

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

  49. #endif

  50. 

  51. 

  52. /* Scaling decisions are generally the same as in the LL&M algorithm;

  53.  * see jidctint.c for more details.  However, we choose to descale

  54.  * (right shift) multiplication products as soon as they are formed,

  55.  * rather than carrying additional fractional bits into subsequent additions.

  56.  * This compromises accuracy slightly, but it lets us save a few shifts.

  57.  * More importantly, 16-bit arithmetic is then adequate (for 8-bit samples)

  58.  * everywhere except in the multiplications proper; this saves a good deal

  59.  * of work on 16-bit-int machines.

  60.  *

  61.  * The dequantized coefficients are not integers because the AA&N scaling

  62.  * factors have been incorporated.  We represent them scaled up by PASS1_BITS,

  63.  * so that the first and second IDCT rounds have the same input scaling.

  64.  * For 8-bit JSAMPLEs, we choose IFAST_SCALE_BITS = PASS1_BITS so as to

  65.  * avoid a descaling shift; this compromises accuracy rather drastically

  66.  * for small quantization table entries, but it saves a lot of shifts.

  67.  * For 12-bit JSAMPLEs, there's no hope of using 16x16 multiplies anyway,

  68.  * so we use a much larger scaling factor to preserve accuracy.

  69.  *

  70.  * A final compromise is to represent the multiplicative constants to only

  71.  * 8 fractional bits, rather than 13.  This saves some shifting work on some

  72.  * machines, and may also reduce the cost of multiplication (since there

  73.  * are fewer one-bits in the constants).

  74.  */

  75. 

  76. #if BITS_IN_JSAMPLE == 8

  77. #define CONST_BITS  8

  78. #define PASS1_BITS  2

  79. #else

  80. #define CONST_BITS  8

  81. #define PASS1_BITS  1		/* lose a little precision to avoid overflow */

  82. #endif

  83. 

  84. /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus

  85.  * causing a lot of useless floating-point operations at run time.

  86.  * To get around this we use the following pre-calculated constants.

  87.  * If you change CONST_BITS you may want to add appropriate values.

  88.  * (With a reasonable C compiler, you can just rely on the FIX() macro...)

  89.  */

  90. 

  91. #if CONST_BITS == 8

  92. #define FIX_1_082392200  ((INT32)  277)		/* FIX(1.082392200) */

  93. #define FIX_1_414213562  ((INT32)  362)		/* FIX(1.414213562) */

  94. #define FIX_1_847759065  ((INT32)  473)		/* FIX(1.847759065) */

  95. #define FIX_2_613125930  ((INT32)  669)		/* FIX(2.613125930) */

  96. #else

  97. #define FIX_1_082392200  FIX(1.082392200)

  98. #define FIX_1_414213562  FIX(1.414213562)

  99. #define FIX_1_847759065  FIX(1.847759065)

  100. #define FIX_2_613125930  FIX(2.613125930)

  101. #endif

  102. 

  103. 

  104. /* We can gain a little more speed, with a further compromise in accuracy,

  105.  * by omitting the addition in a descaling shift.  This yields an incorrectly

  106.  * rounded result half the time...

  107.  */

  108. 

  109. #ifndef USE_ACCURATE_ROUNDING

  110. #undef DESCALE

  111. #define DESCALE(x,n)  RIGHT_SHIFT(x, n)

  112. #endif

  113. 

  114. 

  115. /* Multiply a DCTELEM variable by an INT32 constant, and immediately

  116.  * descale to yield a DCTELEM result.

  117.  */

  118. 

  119. #define MULTIPLY(var,const)  ((DCTELEM) DESCALE((var) * (const), CONST_BITS))

  120. 

  121. 

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

  123.  * entry; produce a DCTELEM result.  For 8-bit data a 16x16->16

  124.  * multiplication will do.  For 12-bit data, the multiplier table is

  125.  * declared INT32, so a 32-bit multiply will be used.

  126.  */

  127. 

  128. #if BITS_IN_JSAMPLE == 8

  129. #define DEQUANTIZE(coef,quantval)  (((IFAST_MULT_TYPE) (coef)) * (quantval))

  130. #else

  131. #define DEQUANTIZE(coef,quantval)  \

  132. 	DESCALE((coef)*(quantval), IFAST_SCALE_BITS-PASS1_BITS)

  133. #endif

  134. 

  135. 

  136. /* Like DESCALE, but applies to a DCTELEM and produces an int.

  137.  * We assume that int right shift is unsigned if INT32 right shift is.

  138.  */

  139. 

  140. #ifdef RIGHT_SHIFT_IS_UNSIGNED

  141. #define ISHIFT_TEMPS	DCTELEM ishift_temp;

  142. #if BITS_IN_JSAMPLE == 8

  143. #define DCTELEMBITS  16		/* DCTELEM may be 16 or 32 bits */

  144. #else

  145. #define DCTELEMBITS  32		/* DCTELEM must be 32 bits */

  146. #endif

  147. #define IRIGHT_SHIFT(x,shft)  \

  148.     ((ishift_temp = (x)) < 0 ? \

  149.      (ishift_temp >> (shft)) | ((~((DCTELEM) 0)) << (DCTELEMBITS-(shft))) : \

  150.      (ishift_temp >> (shft)))

  151. #else

  152. #define ISHIFT_TEMPS

  153. #define IRIGHT_SHIFT(x,shft)	((x) >> (shft))

  154. #endif

  155. 

  156. #ifdef USE_ACCURATE_ROUNDING

  157. #define IDESCALE(x,n)  ((int) IRIGHT_SHIFT((x) + (1 << ((n)-1)), n))

  158. #else

  159. #define IDESCALE(x,n)  ((int) IRIGHT_SHIFT(x, n))

  160. #endif

  161. 

  162. 

  163. /*

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

  165.  */

  166. 

  167. GLOBAL(void)

  168. jpeg_idct_ifast (j_decompress_ptr cinfo, jpeg_component_info * compptr,

  169. 		 JCOEFPTR coef_block,

  170. 		 JSAMPARRAY output_buf, JDIMENSION output_col)

  171. {

  172.   DCTELEM tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;

  173.   DCTELEM tmp10, tmp11, tmp12, tmp13;

  174.   DCTELEM z5, z10, z11, z12, z13;

  175.   JCOEFPTR inptr;

  176.   IFAST_MULT_TYPE * quantptr;

  177.   int * wsptr;

  178.   JSAMPROW outptr;

  179.   JSAMPLE *range_limit = IDCT_range_limit(cinfo);

  180.   int ctr;

  181.   int workspace[DCTSIZE2];	/* buffers data between passes */

  182.   SHIFT_TEMPS			/* for DESCALE */

  183.   ISHIFT_TEMPS			/* for IDESCALE */

  184. 

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

  186. 

  187.   inptr = coef_block;

  188.   quantptr = (IFAST_MULT_TYPE *) compptr->dct_table;

  189.   wsptr = workspace;

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

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

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

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

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

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

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

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

  198.      */

  199.     

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

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

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

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

  204.       /* AC terms all zero */

  205.       int dcval = (int) DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);

  206. 

  207.       wsptr[DCTSIZE*0] = dcval;

  208.       wsptr[DCTSIZE*1] = dcval;

  209.       wsptr[DCTSIZE*2] = dcval;

  210.       wsptr[DCTSIZE*3] = dcval;

  211.       wsptr[DCTSIZE*4] = dcval;

  212.       wsptr[DCTSIZE*5] = dcval;

  213.       wsptr[DCTSIZE*6] = dcval;

  214.       wsptr[DCTSIZE*7] = dcval;

  215.       

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

  217.       quantptr++;

  218.       wsptr++;

  219.       continue;

  220.     }

  221.     

  222.     /* Even part */

  223. 

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

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

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

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

  228. 

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

  230.     tmp11 = tmp0 - tmp2;

  231. 

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

  233.     tmp12 = MULTIPLY(tmp1 - tmp3, FIX_1_414213562) - tmp13; /* 2*c4 */

  234. 

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

  236.     tmp3 = tmp10 - tmp13;

  237.     tmp1 = tmp11 + tmp12;

  238.     tmp2 = tmp11 - tmp12;

  239.     

  240.     /* Odd part */

  241. 

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

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

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

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

  246. 

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

  248.     z10 = tmp6 - tmp5;

  249.     z11 = tmp4 + tmp7;

  250.     z12 = tmp4 - tmp7;

  251. 

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

  253.     tmp11 = MULTIPLY(z11 - z13, FIX_1_414213562); /* 2*c4 */

  254. 

  255.     z5 = MULTIPLY(z10 + z12, FIX_1_847759065); /* 2*c2 */

  256.     tmp10 = MULTIPLY(z12, FIX_1_082392200) - z5; /* 2*(c2-c6) */

  257.     tmp12 = MULTIPLY(z10, - FIX_2_613125930) + z5; /* -2*(c2+c6) */

  258. 

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

  260.     tmp5 = tmp11 - tmp6;

  261.     tmp4 = tmp10 + tmp5;

  262. 

  263.     wsptr[DCTSIZE*0] = (int) (tmp0 + tmp7);

  264.     wsptr[DCTSIZE*7] = (int) (tmp0 - tmp7);

  265.     wsptr[DCTSIZE*1] = (int) (tmp1 + tmp6);

  266.     wsptr[DCTSIZE*6] = (int) (tmp1 - tmp6);

  267.     wsptr[DCTSIZE*2] = (int) (tmp2 + tmp5);

  268.     wsptr[DCTSIZE*5] = (int) (tmp2 - tmp5);

  269.     wsptr[DCTSIZE*4] = (int) (tmp3 + tmp4);

  270.     wsptr[DCTSIZE*3] = (int) (tmp3 - tmp4);

  271. 

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

  273.     quantptr++;

  274.     wsptr++;

  275.   }

  276.   

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

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

  279.   /* and also undo the PASS1_BITS scaling. */

  280. 

  281.   wsptr = workspace;

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

  283.     outptr = output_buf[ctr] + output_col;

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

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

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

  287.      * On machines with very fast multiplication, it's possible that the

  288.      * test takes more time than it's worth.  In that case this section

  289.      * may be commented out.

  290.      */

  291.     

  292. #ifndef NO_ZERO_ROW_TEST

  293.     if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 && wsptr[4] == 0 &&

  294. 	wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) {

  295.       /* AC terms all zero */

  296.       JSAMPLE dcval = range_limit[IDESCALE(wsptr[0], PASS1_BITS+3)

  297. 				  & RANGE_MASK];

  298.       

  299.       outptr[0] = dcval;

  300.       outptr[1] = dcval;

  301.       outptr[2] = dcval;

  302.       outptr[3] = dcval;

  303.       outptr[4] = dcval;

  304.       outptr[5] = dcval;

  305.       outptr[6] = dcval;

  306.       outptr[7] = dcval;

  307. 

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

  309.       continue;

  310.     }

  311. #endif

  312.     

  313.     /* Even part */

  314. 

  315.     tmp10 = ((DCTELEM) wsptr[0] + (DCTELEM) wsptr[4]);

  316.     tmp11 = ((DCTELEM) wsptr[0] - (DCTELEM) wsptr[4]);

  317. 

  318.     tmp13 = ((DCTELEM) wsptr[2] + (DCTELEM) wsptr[6]);

  319.     tmp12 = MULTIPLY((DCTELEM) wsptr[2] - (DCTELEM) wsptr[6], FIX_1_414213562)

  320. 	    - tmp13;

  321. 

  322.     tmp0 = tmp10 + tmp13;

  323.     tmp3 = tmp10 - tmp13;

  324.     tmp1 = tmp11 + tmp12;

  325.     tmp2 = tmp11 - tmp12;

  326. 

  327.     /* Odd part */

  328. 

  329.     z13 = (DCTELEM) wsptr[5] + (DCTELEM) wsptr[3];

  330.     z10 = (DCTELEM) wsptr[5] - (DCTELEM) wsptr[3];

  331.     z11 = (DCTELEM) wsptr[1] + (DCTELEM) wsptr[7];

  332.     z12 = (DCTELEM) wsptr[1] - (DCTELEM) wsptr[7];

  333. 

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

  335.     tmp11 = MULTIPLY(z11 - z13, FIX_1_414213562); /* 2*c4 */

  336. 

  337.     z5 = MULTIPLY(z10 + z12, FIX_1_847759065); /* 2*c2 */

  338.     tmp10 = MULTIPLY(z12, FIX_1_082392200) - z5; /* 2*(c2-c6) */

  339.     tmp12 = MULTIPLY(z10, - FIX_2_613125930) + z5; /* -2*(c2+c6) */

  340. 

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

  342.     tmp5 = tmp11 - tmp6;

  343.     tmp4 = tmp10 + tmp5;

  344. 

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

  346. 

  347.     outptr[0] = range_limit[IDESCALE(tmp0 + tmp7, PASS1_BITS+3)

  348. 			    & RANGE_MASK];

  349.     outptr[7] = range_limit[IDESCALE(tmp0 - tmp7, PASS1_BITS+3)

  350. 			    & RANGE_MASK];

  351.     outptr[1] = range_limit[IDESCALE(tmp1 + tmp6, PASS1_BITS+3)

  352. 			    & RANGE_MASK];

  353.     outptr[6] = range_limit[IDESCALE(tmp1 - tmp6, PASS1_BITS+3)

  354. 			    & RANGE_MASK];

  355.     outptr[2] = range_limit[IDESCALE(tmp2 + tmp5, PASS1_BITS+3)

  356. 			    & RANGE_MASK];

  357.     outptr[5] = range_limit[IDESCALE(tmp2 - tmp5, PASS1_BITS+3)

  358. 			    & RANGE_MASK];

  359.     outptr[4] = range_limit[IDESCALE(tmp3 + tmp4, PASS1_BITS+3)

  360. 			    & RANGE_MASK];

  361.     outptr[3] = range_limit[IDESCALE(tmp3 - tmp4, PASS1_BITS+3)

  362. 			    & RANGE_MASK];

  363. 

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

  365.   }

  366. }

  367. 

  368. #endif /* DCT_IFAST_SUPPORTED */