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

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  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. 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.   dataptr = data;

  154.   for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {

  155.     tmp0 = dataptr[0] + dataptr[7];

  156.     tmp7 = dataptr[0] - dataptr[7];

  157.     tmp1 = dataptr[1] + dataptr[6];

  158.     tmp6 = dataptr[1] - dataptr[6];

  159.     tmp2 = dataptr[2] + dataptr[5];

  160.     tmp5 = dataptr[2] - dataptr[5];

  161.     tmp3 = dataptr[3] + dataptr[4];

  162.     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.     tmp10 = tmp0 + tmp3;

  169.     tmp13 = tmp0 - tmp3;

  170.     tmp11 = tmp1 + tmp2;

  171.     tmp12 = tmp1 - tmp2;

  172. 

  173.     dataptr[0] = (DCTELEM) ((tmp10 + tmp11) << PASS1_BITS);

  174.     dataptr[4] = (DCTELEM) ((tmp10 - tmp11) << PASS1_BITS);

  175. 

  176.     z1 = MULTIPLY(tmp12 + tmp13, FIX_0_541196100);

  177.     dataptr[2] = (DCTELEM) DESCALE(z1 + MULTIPLY(tmp13, FIX_0_765366865),

  178. 				   CONST_BITS-PASS1_BITS);

  179.     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.     z1 = tmp4 + tmp7;

  188.     z2 = tmp5 + tmp6;

  189.     z3 = tmp4 + tmp6;

  190.     z4 = tmp5 + tmp7;

  191.     z5 = MULTIPLY(z3 + z4, FIX_1_175875602); /* sqrt(2) * c3 */

  192. 

  193.     tmp4 = MULTIPLY(tmp4, FIX_0_298631336); /* sqrt(2) * (-c1+c3+c5-c7) */

  194.     tmp5 = MULTIPLY(tmp5, FIX_2_053119869); /* sqrt(2) * ( c1+c3-c5+c7) */

  195.     tmp6 = MULTIPLY(tmp6, FIX_3_072711026); /* sqrt(2) * ( c1+c3+c5-c7) */

  196.     tmp7 = MULTIPLY(tmp7, FIX_1_501321110); /* sqrt(2) * ( c1+c3-c5-c7) */

  197.     z1 = MULTIPLY(z1, - FIX_0_899976223); /* sqrt(2) * (c7-c3) */

  198.     z2 = MULTIPLY(z2, - FIX_2_562915447); /* sqrt(2) * (-c1-c3) */

  199.     z3 = MULTIPLY(z3, - FIX_1_961570560); /* sqrt(2) * (-c3-c5) */

  200.     z4 = MULTIPLY(z4, - FIX_0_390180644); /* sqrt(2) * (c5-c3) */

  201. 

  202.     z3 += z5;

  203.     z4 += z5;

  204. 

  205.     dataptr[7] = (DCTELEM) DESCALE(tmp4 + z1 + z3, CONST_BITS-PASS1_BITS);

  206.     dataptr[5] = (DCTELEM) DESCALE(tmp5 + z2 + z4, CONST_BITS-PASS1_BITS);

  207.     dataptr[3] = (DCTELEM) DESCALE(tmp6 + z2 + z3, CONST_BITS-PASS1_BITS);

  208.     dataptr[1] = (DCTELEM) DESCALE(tmp7 + z1 + z4, CONST_BITS-PASS1_BITS);

  209. 

  210.     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.   dataptr = data;

  219.   for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {

  220.     tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7];

  221.     tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7];

  222.     tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6];

  223.     tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6];

  224.     tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5];

  225.     tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5];

  226.     tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4];

  227.     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.     tmp10 = tmp0 + tmp3;

  234.     tmp13 = tmp0 - tmp3;

  235.     tmp11 = tmp1 + tmp2;

  236.     tmp12 = tmp1 - tmp2;

  237. 

  238.     dataptr[DCTSIZE*0] = (DCTELEM) DESCALE(tmp10 + tmp11, PASS1_BITS);

  239.     dataptr[DCTSIZE*4] = (DCTELEM) DESCALE(tmp10 - tmp11, PASS1_BITS);

  240. 

  241.     z1 = MULTIPLY(tmp12 + tmp13, FIX_0_541196100);

  242.     dataptr[DCTSIZE*2] = (DCTELEM) DESCALE(z1 + MULTIPLY(tmp13, FIX_0_765366865),

  243. 					   CONST_BITS+PASS1_BITS);

  244.     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.     z1 = tmp4 + tmp7;

  253.     z2 = tmp5 + tmp6;

  254.     z3 = tmp4 + tmp6;

  255.     z4 = tmp5 + tmp7;

  256.     z5 = MULTIPLY(z3 + z4, FIX_1_175875602); /* sqrt(2) * c3 */

  257. 

  258.     tmp4 = MULTIPLY(tmp4, FIX_0_298631336); /* sqrt(2) * (-c1+c3+c5-c7) */

  259.     tmp5 = MULTIPLY(tmp5, FIX_2_053119869); /* sqrt(2) * ( c1+c3-c5+c7) */

  260.     tmp6 = MULTIPLY(tmp6, FIX_3_072711026); /* sqrt(2) * ( c1+c3+c5-c7) */

  261.     tmp7 = MULTIPLY(tmp7, FIX_1_501321110); /* sqrt(2) * ( c1+c3-c5-c7) */

  262.     z1 = MULTIPLY(z1, - FIX_0_899976223); /* sqrt(2) * (c7-c3) */

  263.     z2 = MULTIPLY(z2, - FIX_2_562915447); /* sqrt(2) * (-c1-c3) */

  264.     z3 = MULTIPLY(z3, - FIX_1_961570560); /* sqrt(2) * (-c3-c5) */

  265.     z4 = MULTIPLY(z4, - FIX_0_390180644); /* sqrt(2) * (c5-c3) */

  266. 

  267.     z3 += z5;

  268.     z4 += z5;

  269. 

  270.     dataptr[DCTSIZE*7] = (DCTELEM) DESCALE(tmp4 + z1 + z3,

  271. 					   CONST_BITS+PASS1_BITS);

  272.     dataptr[DCTSIZE*5] = (DCTELEM) DESCALE(tmp5 + z2 + z4,

  273. 					   CONST_BITS+PASS1_BITS);

  274.     dataptr[DCTSIZE*3] = (DCTELEM) DESCALE(tmp6 + z2 + z3,

  275. 					   CONST_BITS+PASS1_BITS);

  276.     dataptr[DCTSIZE*1] = (DCTELEM) DESCALE(tmp7 + z1 + z4,

  277. 					   CONST_BITS+PASS1_BITS);

  278. 

  279.     dataptr++;			/* advance pointer to next column */

  280.   }

  281. }

  282. 

  283. #endif /* DCT_ISLOW_SUPPORTED */