jidctred.c

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Hash : 19c791cd
Author :
Date : 2018-03-08T10:55:20

Improve code formatting consistency

With rare exceptions ...
- Always separate line continuation characters by one space from
  preceding code.
- Always use two-space indentation.  Never use tabs.
- Always use K&R-style conditional blocks.
- Always surround operators with spaces, except in raw assembly code.
- Always put a space after, but not before, a comma.
- Never put a space between type casts and variables/function calls.
- Never put a space between the function name and the argument list in
  function declarations and prototypes.
- Always surround braces ('{' and '}') with spaces.
- Always surround statements (if, for, else, catch, while, do, switch)
  with spaces.
- Always attach pointer symbols ('*' and '**') to the variable or
  function name.
- Always precede pointer symbols ('*' and '**') by a space in type
  casts.
- Use the MIN() macro from jpegint.h within the libjpeg and TurboJPEG
  API libraries (using min() from tjutil.h is still necessary for
  TJBench.)
- Where it makes sense (particularly in the TurboJPEG code), put a blank
  line after variable declaration blocks.
- Always separate statements in one-liners by two spaces.

The purpose of this was to ease maintenance on my part and also to make
it easier for contributors to figure out how to format patch
submissions.  This was admittedly confusing (even to me sometimes) when
we had 3 or 4 different style conventions in the same source tree.  The
new convention is more consistent with the formatting of other OSS code
bases.

This commit corrects deviations from the chosen formatting style in the
libjpeg API code and reformats the TurboJPEG API code such that it
conforms to the same standard.

NOTES:
- Although it is no longer necessary for the function name in function
  declarations to begin in Column 1 (this was historically necessary
  because of the ansi2knr utility, which allowed libjpeg to be built
  with non-ANSI compilers), we retain that formatting for the libjpeg
  code because it improves readability when using libjpeg's function
  attribute macros (GLOBAL(), etc.)
- This reformatting project was accomplished with the help of AStyle and
  Uncrustify, although neither was completely up to the task, and thus
  a great deal of manual tweaking was required.  Note to developers of
  code formatting utilities:  the libjpeg-turbo code base is an
  excellent test bed, because AFAICT, it breaks every single one of the
  utilities that are currently available.
- The legacy (MMX, SSE, 3DNow!) assembly code for i386 has been
  formatted to match the SSE2 code (refer to
  ff5685d5344273df321eb63a005eaae19d2496e3.)  I hadn't intended to
  bother with this, but the Loongson MMI implementation demonstrated
  that there is still academic value to the MMX implementation, as an
  algorithmic model for other 64-bit vector implementations.  Thus, it
  is desirable to improve its readability in the same manner as that of
  the SSE2 implementation.

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jidctred.c

/*
 * jidctred.c
 *
 * This file was part of the Independent JPEG Group's software.
 * Copyright (C) 1994-1998, Thomas G. Lane.
 * libjpeg-turbo Modifications:
 * Copyright (C) 2015, D. R. Commander.
 * For conditions of distribution and use, see the accompanying README.ijg
 * file.
 *
 * This file contains inverse-DCT routines that produce reduced-size output:
 * either 4x4, 2x2, or 1x1 pixels from an 8x8 DCT block.
 *
 * The implementation is based on the Loeffler, Ligtenberg and Moschytz (LL&M)
 * algorithm used in jidctint.c.  We simply replace each 8-to-8 1-D IDCT step
 * with an 8-to-4 step that produces the four averages of two adjacent outputs
 * (or an 8-to-2 step producing two averages of four outputs, for 2x2 output).
 * These steps were derived by computing the corresponding values at the end
 * of the normal LL&M code, then simplifying as much as possible.
 *
 * 1x1 is trivial: just take the DC coefficient divided by 8.
 *
 * See jidctint.c for additional comments.
 */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jdct.h"               /* Private declarations for DCT subsystem */

#ifdef IDCT_SCALING_SUPPORTED


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

#if DCTSIZE != 8
  Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
#endif


/* Scaling is the same as in jidctint.c. */

#if BITS_IN_JSAMPLE == 8
#define CONST_BITS  13
#define PASS1_BITS  2
#else
#define CONST_BITS  13
#define PASS1_BITS  1           /* lose a little precision to avoid overflow */
#endif

/* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
 * causing a lot of useless floating-point operations at run time.
 * To get around this we use the following pre-calculated constants.
 * If you change CONST_BITS you may want to add appropriate values.
 * (With a reasonable C compiler, you can just rely on the FIX() macro...)
 */

#if CONST_BITS == 13
#define FIX_0_211164243  ((JLONG)1730)          /* FIX(0.211164243) */
#define FIX_0_509795579  ((JLONG)4176)          /* FIX(0.509795579) */
#define FIX_0_601344887  ((JLONG)4926)          /* FIX(0.601344887) */
#define FIX_0_720959822  ((JLONG)5906)          /* FIX(0.720959822) */
#define FIX_0_765366865  ((JLONG)6270)          /* FIX(0.765366865) */
#define FIX_0_850430095  ((JLONG)6967)          /* FIX(0.850430095) */
#define FIX_0_899976223  ((JLONG)7373)          /* FIX(0.899976223) */
#define FIX_1_061594337  ((JLONG)8697)          /* FIX(1.061594337) */
#define FIX_1_272758580  ((JLONG)10426)         /* FIX(1.272758580) */
#define FIX_1_451774981  ((JLONG)11893)         /* FIX(1.451774981) */
#define FIX_1_847759065  ((JLONG)15137)         /* FIX(1.847759065) */
#define FIX_2_172734803  ((JLONG)17799)         /* FIX(2.172734803) */
#define FIX_2_562915447  ((JLONG)20995)         /* FIX(2.562915447) */
#define FIX_3_624509785  ((JLONG)29692)         /* FIX(3.624509785) */
#else
#define FIX_0_211164243  FIX(0.211164243)
#define FIX_0_509795579  FIX(0.509795579)
#define FIX_0_601344887  FIX(0.601344887)
#define FIX_0_720959822  FIX(0.720959822)
#define FIX_0_765366865  FIX(0.765366865)
#define FIX_0_850430095  FIX(0.850430095)
#define FIX_0_899976223  FIX(0.899976223)
#define FIX_1_061594337  FIX(1.061594337)
#define FIX_1_272758580  FIX(1.272758580)
#define FIX_1_451774981  FIX(1.451774981)
#define FIX_1_847759065  FIX(1.847759065)
#define FIX_2_172734803  FIX(2.172734803)
#define FIX_2_562915447  FIX(2.562915447)
#define FIX_3_624509785  FIX(3.624509785)
#endif


/* Multiply a JLONG variable by a JLONG constant to yield a JLONG result.
 * For 8-bit samples with the recommended scaling, all the variable
 * and constant values involved are no more than 16 bits wide, so a
 * 16x16->32 bit multiply can be used instead of a full 32x32 multiply.
 * For 12-bit samples, a full 32-bit multiplication will be needed.
 */

#if BITS_IN_JSAMPLE == 8
#define MULTIPLY(var, const)  MULTIPLY16C16(var, const)
#else
#define MULTIPLY(var, const)  ((var) * (const))
#endif


/* Dequantize a coefficient by multiplying it by the multiplier-table
 * entry; produce an int result.  In this module, both inputs and result
 * are 16 bits or less, so either int or short multiply will work.
 */

#define DEQUANTIZE(coef, quantval)  (((ISLOW_MULT_TYPE)(coef)) * (quantval))


/*
 * Perform dequantization and inverse DCT on one block of coefficients,
 * producing a reduced-size 4x4 output block.
 */

GLOBAL(void)
jpeg_idct_4x4(j_decompress_ptr cinfo, jpeg_component_info *compptr,
              JCOEFPTR coef_block, JSAMPARRAY output_buf,
              JDIMENSION output_col)
{
  JLONG tmp0, tmp2, tmp10, tmp12;
  JLONG z1, z2, z3, z4;
  JCOEFPTR inptr;
  ISLOW_MULT_TYPE *quantptr;
  int *wsptr;
  JSAMPROW outptr;
  JSAMPLE *range_limit = IDCT_range_limit(cinfo);
  int ctr;
  int workspace[DCTSIZE * 4];   /* buffers data between passes */
  SHIFT_TEMPS

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

  inptr = coef_block;
  quantptr = (ISLOW_MULT_TYPE *)compptr->dct_table;
  wsptr = workspace;
  for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) {
    /* Don't bother to process column 4, because second pass won't use it */
    if (ctr == DCTSIZE - 4)
      continue;
    if (inptr[DCTSIZE * 1] == 0 && inptr[DCTSIZE * 2] == 0 &&
        inptr[DCTSIZE * 3] == 0 && inptr[DCTSIZE * 5] == 0 &&
        inptr[DCTSIZE * 6] == 0 && inptr[DCTSIZE * 7] == 0) {
      /* AC terms all zero; we need not examine term 4 for 4x4 output */
      int dcval = LEFT_SHIFT(DEQUANTIZE(inptr[DCTSIZE * 0],
                                        quantptr[DCTSIZE * 0]), PASS1_BITS);

      wsptr[DCTSIZE * 0] = dcval;
      wsptr[DCTSIZE * 1] = dcval;
      wsptr[DCTSIZE * 2] = dcval;
      wsptr[DCTSIZE * 3] = dcval;

      continue;
    }

    /* Even part */

    tmp0 = DEQUANTIZE(inptr[DCTSIZE * 0], quantptr[DCTSIZE * 0]);
    tmp0 = LEFT_SHIFT(tmp0, CONST_BITS + 1);

    z2 = DEQUANTIZE(inptr[DCTSIZE * 2], quantptr[DCTSIZE * 2]);
    z3 = DEQUANTIZE(inptr[DCTSIZE * 6], quantptr[DCTSIZE * 6]);

    tmp2 = MULTIPLY(z2, FIX_1_847759065) + MULTIPLY(z3, -FIX_0_765366865);

    tmp10 = tmp0 + tmp2;
    tmp12 = tmp0 - tmp2;

    /* Odd part */

    z1 = DEQUANTIZE(inptr[DCTSIZE * 7], quantptr[DCTSIZE * 7]);
    z2 = DEQUANTIZE(inptr[DCTSIZE * 5], quantptr[DCTSIZE * 5]);
    z3 = DEQUANTIZE(inptr[DCTSIZE * 3], quantptr[DCTSIZE * 3]);
    z4 = DEQUANTIZE(inptr[DCTSIZE * 1], quantptr[DCTSIZE * 1]);

    tmp0 = MULTIPLY(z1, -FIX_0_211164243) + /* sqrt(2) * ( c3-c1) */
           MULTIPLY(z2,  FIX_1_451774981) + /* sqrt(2) * ( c3+c7) */
           MULTIPLY(z3, -FIX_2_172734803) + /* sqrt(2) * (-c1-c5) */
           MULTIPLY(z4,  FIX_1_061594337);  /* sqrt(2) * ( c5+c7) */

    tmp2 = MULTIPLY(z1, -FIX_0_509795579) + /* sqrt(2) * (c7-c5) */
           MULTIPLY(z2, -FIX_0_601344887) + /* sqrt(2) * (c5-c1) */
           MULTIPLY(z3,  FIX_0_899976223) + /* sqrt(2) * (c3-c7) */
           MULTIPLY(z4,  FIX_2_562915447);  /* sqrt(2) * (c1+c3) */

    /* Final output stage */

    wsptr[DCTSIZE * 0] =
      (int)DESCALE(tmp10 + tmp2, CONST_BITS - PASS1_BITS + 1);
    wsptr[DCTSIZE * 3] =
      (int)DESCALE(tmp10 - tmp2, CONST_BITS - PASS1_BITS + 1);
    wsptr[DCTSIZE * 1] =
      (int)DESCALE(tmp12 + tmp0, CONST_BITS - PASS1_BITS + 1);
    wsptr[DCTSIZE * 2] =
      (int)DESCALE(tmp12 - tmp0, CONST_BITS - PASS1_BITS + 1);
  }

  /* Pass 2: process 4 rows from work array, store into output array. */

  wsptr = workspace;
  for (ctr = 0; ctr < 4; ctr++) {
    outptr = output_buf[ctr] + output_col;
    /* It's not clear whether a zero row test is worthwhile here ... */

#ifndef NO_ZERO_ROW_TEST
    if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 &&
        wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) {
      /* AC terms all zero */
      JSAMPLE dcval = range_limit[(int)DESCALE((JLONG)wsptr[0],
                                               PASS1_BITS + 3) & RANGE_MASK];

      outptr[0] = dcval;
      outptr[1] = dcval;
      outptr[2] = dcval;
      outptr[3] = dcval;

      wsptr += DCTSIZE;         /* advance pointer to next row */
      continue;
    }
#endif

    /* Even part */

    tmp0 = LEFT_SHIFT((JLONG)wsptr[0], CONST_BITS + 1);

    tmp2 = MULTIPLY((JLONG)wsptr[2],  FIX_1_847759065) +
           MULTIPLY((JLONG)wsptr[6], -FIX_0_765366865);

    tmp10 = tmp0 + tmp2;
    tmp12 = tmp0 - tmp2;

    /* Odd part */

    z1 = (JLONG)wsptr[7];
    z2 = (JLONG)wsptr[5];
    z3 = (JLONG)wsptr[3];
    z4 = (JLONG)wsptr[1];

    tmp0 = MULTIPLY(z1, -FIX_0_211164243) + /* sqrt(2) * ( c3-c1) */
           MULTIPLY(z2,  FIX_1_451774981) + /* sqrt(2) * ( c3+c7) */
           MULTIPLY(z3, -FIX_2_172734803) + /* sqrt(2) * (-c1-c5) */
           MULTIPLY(z4,  FIX_1_061594337);  /* sqrt(2) * ( c5+c7) */

    tmp2 = MULTIPLY(z1, -FIX_0_509795579) + /* sqrt(2) * (c7-c5) */
           MULTIPLY(z2, -FIX_0_601344887) + /* sqrt(2) * (c5-c1) */
           MULTIPLY(z3, FIX_0_899976223) +  /* sqrt(2) * (c3-c7) */
           MULTIPLY(z4, FIX_2_562915447);   /* sqrt(2) * (c1+c3) */

    /* Final output stage */

    outptr[0] = range_limit[(int)DESCALE(tmp10 + tmp2,
                                         CONST_BITS + PASS1_BITS + 3 + 1) &
                            RANGE_MASK];
    outptr[3] = range_limit[(int)DESCALE(tmp10 - tmp2,
                                         CONST_BITS + PASS1_BITS + 3 + 1) &
                            RANGE_MASK];
    outptr[1] = range_limit[(int)DESCALE(tmp12 + tmp0,
                                         CONST_BITS + PASS1_BITS + 3 + 1) &
                            RANGE_MASK];
    outptr[2] = range_limit[(int)DESCALE(tmp12 - tmp0,
                                         CONST_BITS + PASS1_BITS + 3 + 1) &
                            RANGE_MASK];

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


/*
 * Perform dequantization and inverse DCT on one block of coefficients,
 * producing a reduced-size 2x2 output block.
 */

GLOBAL(void)
jpeg_idct_2x2(j_decompress_ptr cinfo, jpeg_component_info *compptr,
              JCOEFPTR coef_block, JSAMPARRAY output_buf,
              JDIMENSION output_col)
{
  JLONG tmp0, tmp10, z1;
  JCOEFPTR inptr;
  ISLOW_MULT_TYPE *quantptr;
  int *wsptr;
  JSAMPROW outptr;
  JSAMPLE *range_limit = IDCT_range_limit(cinfo);
  int ctr;
  int workspace[DCTSIZE * 2];   /* buffers data between passes */
  SHIFT_TEMPS

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

  inptr = coef_block;
  quantptr = (ISLOW_MULT_TYPE *)compptr->dct_table;
  wsptr = workspace;
  for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) {
    /* Don't bother to process columns 2,4,6 */
    if (ctr == DCTSIZE - 2 || ctr == DCTSIZE - 4 || ctr == DCTSIZE - 6)
      continue;
    if (inptr[DCTSIZE * 1] == 0 && inptr[DCTSIZE * 3] == 0 &&
        inptr[DCTSIZE * 5] == 0 && inptr[DCTSIZE * 7] == 0) {
      /* AC terms all zero; we need not examine terms 2,4,6 for 2x2 output */
      int dcval = LEFT_SHIFT(DEQUANTIZE(inptr[DCTSIZE * 0],
                             quantptr[DCTSIZE * 0]), PASS1_BITS);

      wsptr[DCTSIZE * 0] = dcval;
      wsptr[DCTSIZE * 1] = dcval;

      continue;
    }

    /* Even part */

    z1 = DEQUANTIZE(inptr[DCTSIZE * 0], quantptr[DCTSIZE * 0]);
    tmp10 = LEFT_SHIFT(z1, CONST_BITS + 2);

    /* Odd part */

    z1 = DEQUANTIZE(inptr[DCTSIZE * 7], quantptr[DCTSIZE * 7]);
    tmp0 = MULTIPLY(z1, -FIX_0_720959822);  /* sqrt(2) * ( c7-c5+c3-c1) */
    z1 = DEQUANTIZE(inptr[DCTSIZE * 5], quantptr[DCTSIZE * 5]);
    tmp0 += MULTIPLY(z1, FIX_0_850430095);  /* sqrt(2) * (-c1+c3+c5+c7) */
    z1 = DEQUANTIZE(inptr[DCTSIZE * 3], quantptr[DCTSIZE * 3]);
    tmp0 += MULTIPLY(z1, -FIX_1_272758580); /* sqrt(2) * (-c1+c3-c5-c7) */
    z1 = DEQUANTIZE(inptr[DCTSIZE * 1], quantptr[DCTSIZE * 1]);
    tmp0 += MULTIPLY(z1, FIX_3_624509785);  /* sqrt(2) * ( c1+c3+c5+c7) */

    /* Final output stage */

    wsptr[DCTSIZE * 0] =
      (int)DESCALE(tmp10 + tmp0, CONST_BITS - PASS1_BITS + 2);
    wsptr[DCTSIZE * 1] =
      (int)DESCALE(tmp10 - tmp0, CONST_BITS - PASS1_BITS + 2);
  }

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

  wsptr = workspace;
  for (ctr = 0; ctr < 2; ctr++) {
    outptr = output_buf[ctr] + output_col;
    /* It's not clear whether a zero row test is worthwhile here ... */

#ifndef NO_ZERO_ROW_TEST
    if (wsptr[1] == 0 && wsptr[3] == 0 && wsptr[5] == 0 && wsptr[7] == 0) {
      /* AC terms all zero */
      JSAMPLE dcval = range_limit[(int)DESCALE((JLONG)wsptr[0],
                                               PASS1_BITS + 3) & RANGE_MASK];

      outptr[0] = dcval;
      outptr[1] = dcval;

      wsptr += DCTSIZE;         /* advance pointer to next row */
      continue;
    }
#endif

    /* Even part */

    tmp10 = LEFT_SHIFT((JLONG)wsptr[0], CONST_BITS + 2);

    /* Odd part */

    tmp0 = MULTIPLY((JLONG)wsptr[7], -FIX_0_720959822) + /* sqrt(2) * ( c7-c5+c3-c1) */
           MULTIPLY((JLONG)wsptr[5],  FIX_0_850430095) + /* sqrt(2) * (-c1+c3+c5+c7) */
           MULTIPLY((JLONG)wsptr[3], -FIX_1_272758580) + /* sqrt(2) * (-c1+c3-c5-c7) */
           MULTIPLY((JLONG)wsptr[1],  FIX_3_624509785);  /* sqrt(2) * ( c1+c3+c5+c7) */

    /* Final output stage */

    outptr[0] = range_limit[(int)DESCALE(tmp10 + tmp0,
                                         CONST_BITS + PASS1_BITS + 3 + 2) &
                            RANGE_MASK];
    outptr[1] = range_limit[(int)DESCALE(tmp10 - tmp0,
                                         CONST_BITS + PASS1_BITS + 3 + 2) &
                            RANGE_MASK];

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


/*
 * Perform dequantization and inverse DCT on one block of coefficients,
 * producing a reduced-size 1x1 output block.
 */

GLOBAL(void)
jpeg_idct_1x1(j_decompress_ptr cinfo, jpeg_component_info *compptr,
              JCOEFPTR coef_block, JSAMPARRAY output_buf,
              JDIMENSION output_col)
{
  int dcval;
  ISLOW_MULT_TYPE *quantptr;
  JSAMPLE *range_limit = IDCT_range_limit(cinfo);
  SHIFT_TEMPS

  /* We hardly need an inverse DCT routine for this: just take the
   * average pixel value, which is one-eighth of the DC coefficient.
   */
  quantptr = (ISLOW_MULT_TYPE *)compptr->dct_table;
  dcval = DEQUANTIZE(coef_block[0], quantptr[0]);
  dcval = (int)DESCALE((JLONG)dcval, 3);

  output_buf[0][output_col] = range_limit[dcval & RANGE_MASK];
}

#endif /* IDCT_SCALING_SUPPORTED */

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jidctred.c