The Tor Browser: media/libjpeg/jidctfst.c@b8a032363ba2 (annotated)

media/libjpeg/jidctfst.c@b8a032363ba2 (annotated)

media/libjpeg/jidctfst.c

Thu, 22 Jan 2015 13:21:57 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Thu, 22 Jan 2015 13:21:57 +0100
branch: TOR_BUG_9701
changeset 15: b8a032363ba2
permissions: -rw-r--r--

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

 /*
  * jidctfst.c
  *
  * Copyright (C) 1994-1998, Thomas G. Lane.
  * This file is part of the Independent JPEG Group's software.
  * For conditions of distribution and use, see the accompanying README file.
  *
  * This file contains a fast, not so accurate integer implementation of the
  * inverse DCT (Discrete Cosine Transform).  In the IJG code, this routine
  * must also perform dequantization of the input coefficients.
  *
  * A 2-D IDCT can be done by 1-D IDCT on each column followed by 1-D IDCT
  * on each row (or vice versa, but it's more convenient to emit a row at
  * a time).  Direct algorithms are also available, but they are much more
  * complex and seem not to be any faster when reduced to code.
  *
  * This implementation is based on Arai, Agui, and Nakajima's algorithm for
  * scaled DCT.  Their original paper (Trans. IEICE E-71(11):1095) is in
  * Japanese, but the algorithm is described in the Pennebaker & Mitchell
  * JPEG textbook (see REFERENCES section in file README).  The following code
  * is based directly on figure 4-8 in P&M.
  * While an 8-point DCT cannot be done in less than 11 multiplies, it is
  * possible to arrange the computation so that many of the multiplies are
  * simple scalings of the final outputs.  These multiplies can then be
  * folded into the multiplications or divisions by the JPEG quantization
  * table entries.  The AA&N method leaves only 5 multiplies and 29 adds
  * to be done in the DCT itself.
  * The primary disadvantage of this method is that with fixed-point math,
  * accuracy is lost due to imprecise representation of the scaled
  * quantization values.  The smaller the quantization table entry, the less
  * precise the scaled value, so this implementation does worse with high-
  * quality-setting files than with low-quality ones.
  */
 #define JPEG_INTERNALS
 #include "jinclude.h"
 #include "jpeglib.h"
 #include "jdct.h"		/* Private declarations for DCT subsystem */
 #ifdef DCT_IFAST_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 decisions are generally the same as in the LL&M algorithm;
  * see jidctint.c for more details.  However, we choose to descale
  * (right shift) multiplication products as soon as they are formed,
  * rather than carrying additional fractional bits into subsequent additions.
  * This compromises accuracy slightly, but it lets us save a few shifts.
  * More importantly, 16-bit arithmetic is then adequate (for 8-bit samples)
  * everywhere except in the multiplications proper; this saves a good deal
  * of work on 16-bit-int machines.
  *
  * The dequantized coefficients are not integers because the AA&N scaling
  * factors have been incorporated.  We represent them scaled up by PASS1_BITS,
  * so that the first and second IDCT rounds have the same input scaling.
  * For 8-bit JSAMPLEs, we choose IFAST_SCALE_BITS = PASS1_BITS so as to
  * avoid a descaling shift; this compromises accuracy rather drastically
  * for small quantization table entries, but it saves a lot of shifts.
  * For 12-bit JSAMPLEs, there's no hope of using 16x16 multiplies anyway,
  * so we use a much larger scaling factor to preserve accuracy.
  *
  * A final compromise is to represent the multiplicative constants to only
  * 8 fractional bits, rather than 13.  This saves some shifting work on some
  * machines, and may also reduce the cost of multiplication (since there
  * are fewer one-bits in the constants).
  */
 #if BITS_IN_JSAMPLE == 8
 #define CONST_BITS  8
 #define PASS1_BITS  2
 #else
 #define CONST_BITS  8
 #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 == 8
 #define FIX_1_082392200  ((INT32)  277)		/* FIX(1.082392200) */
 #define FIX_1_414213562  ((INT32)  362)		/* FIX(1.414213562) */
 #define FIX_1_847759065  ((INT32)  473)		/* FIX(1.847759065) */
 #define FIX_2_613125930  ((INT32)  669)		/* FIX(2.613125930) */
 #else
 #define FIX_1_082392200  FIX(1.082392200)
 #define FIX_1_414213562  FIX(1.414213562)
 #define FIX_1_847759065  FIX(1.847759065)
 #define FIX_2_613125930  FIX(2.613125930)
 #endif
 /* We can gain a little more speed, with a further compromise in accuracy,
  * by omitting the addition in a descaling shift.  This yields an incorrectly
  * rounded result half the time...
  */
 #ifndef USE_ACCURATE_ROUNDING
 #undef DESCALE
 #define DESCALE(x,n)  RIGHT_SHIFT(x, n)
 #endif
 /* Multiply a DCTELEM variable by an INT32 constant, and immediately
  * descale to yield a DCTELEM result.
  */
 #define MULTIPLY(var,const)  ((DCTELEM) DESCALE((var) * (const), CONST_BITS))
 /* Dequantize a coefficient by multiplying it by the multiplier-table
  * entry; produce a DCTELEM result.  For 8-bit data a 16x16->16
  * multiplication will do.  For 12-bit data, the multiplier table is
  * declared INT32, so a 32-bit multiply will be used.
  */
 #if BITS_IN_JSAMPLE == 8
 #define DEQUANTIZE(coef,quantval)  (((IFAST_MULT_TYPE) (coef)) * (quantval))
 #else
 #define DEQUANTIZE(coef,quantval)  \
 	DESCALE((coef)*(quantval), IFAST_SCALE_BITS-PASS1_BITS)
 #endif
 /* Like DESCALE, but applies to a DCTELEM and produces an int.
  * We assume that int right shift is unsigned if INT32 right shift is.
  */
 #ifdef RIGHT_SHIFT_IS_UNSIGNED
 #define ISHIFT_TEMPS	DCTELEM ishift_temp;
 #if BITS_IN_JSAMPLE == 8
 #define DCTELEMBITS  16		/* DCTELEM may be 16 or 32 bits */
 #else
 #define DCTELEMBITS  32		/* DCTELEM must be 32 bits */
 #endif
 #define IRIGHT_SHIFT(x,shft)  \
     ((ishift_temp = (x)) < 0 ? \
      (ishift_temp >> (shft)) | ((~((DCTELEM) 0)) << (DCTELEMBITS-(shft))) : \
      (ishift_temp >> (shft)))
 #else
 #define ISHIFT_TEMPS
 #define IRIGHT_SHIFT(x,shft)	((x) >> (shft))
 #endif
 #ifdef USE_ACCURATE_ROUNDING
 #define IDESCALE(x,n)  ((int) IRIGHT_SHIFT((x) + (1 << ((n)-1)), n))
 #else
 #define IDESCALE(x,n)  ((int) IRIGHT_SHIFT(x, n))
 #endif
 /*
  * Perform dequantization and inverse DCT on one block of coefficients.
  */
 GLOBAL(void)
 jpeg_idct_ifast (j_decompress_ptr cinfo, jpeg_component_info * compptr,
 		 JCOEFPTR coef_block,
 		 JSAMPARRAY output_buf, JDIMENSION output_col)
 {
   DCTELEM tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
   DCTELEM tmp10, tmp11, tmp12, tmp13;
   DCTELEM z5, z10, z11, z12, z13;
   JCOEFPTR inptr;
   IFAST_MULT_TYPE * quantptr;
   int * wsptr;
   JSAMPROW outptr;
   JSAMPLE *range_limit = IDCT_range_limit(cinfo);
   int ctr;
   int workspace[DCTSIZE2];	/* buffers data between passes */
   SHIFT_TEMPS			/* for DESCALE */
   ISHIFT_TEMPS			/* for IDESCALE */
   /* Pass 1: process columns from input, store into work array. */
   inptr = coef_block;
   quantptr = (IFAST_MULT_TYPE *) compptr->dct_table;
   wsptr = workspace;
   for (ctr = DCTSIZE; ctr > 0; ctr--) {
     /* Due to quantization, we will usually find that many of the input
      * coefficients are zero, especially the AC terms.  We can exploit this
      * by short-circuiting the IDCT calculation for any column in which all
      * the AC terms are zero.  In that case each output is equal to the
      * DC coefficient (with scale factor as needed).
      * With typical images and quantization tables, half or more of the
      * column DCT calculations can be simplified this way.
      */
     if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*2] == 0 &&
 	inptr[DCTSIZE*3] == 0 && inptr[DCTSIZE*4] == 0 &&
 	inptr[DCTSIZE*5] == 0 && inptr[DCTSIZE*6] == 0 &&
 	inptr[DCTSIZE*7] == 0) {
       /* AC terms all zero */
       int dcval = (int) DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
       wsptr[DCTSIZE*0] = dcval;
       wsptr[DCTSIZE*1] = dcval;
       wsptr[DCTSIZE*2] = dcval;
       wsptr[DCTSIZE*3] = dcval;
       wsptr[DCTSIZE*4] = dcval;
       wsptr[DCTSIZE*5] = dcval;
       wsptr[DCTSIZE*6] = dcval;
       wsptr[DCTSIZE*7] = dcval;
       inptr++;			/* advance pointers to next column */
       quantptr++;
       wsptr++;
       continue;
     }
     /* Even part */
     tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
     tmp1 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]);
     tmp2 = DEQUANTIZE(inptr[DCTSIZE*4], quantptr[DCTSIZE*4]);
     tmp3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]);
     tmp10 = tmp0 + tmp2;	/* phase 3 */
     tmp11 = tmp0 - tmp2;
     tmp13 = tmp1 + tmp3;	/* phases 5-3 */
     tmp12 = MULTIPLY(tmp1 - tmp3, FIX_1_414213562) - tmp13; /* 2*c4 */
     tmp0 = tmp10 + tmp13;	/* phase 2 */
     tmp3 = tmp10 - tmp13;
     tmp1 = tmp11 + tmp12;
     tmp2 = tmp11 - tmp12;
     /* Odd part */
     tmp4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
     tmp5 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
     tmp6 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
     tmp7 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
     z13 = tmp6 + tmp5;		/* phase 6 */
     z10 = tmp6 - tmp5;
     z11 = tmp4 + tmp7;
     z12 = tmp4 - tmp7;
     tmp7 = z11 + z13;		/* phase 5 */
     tmp11 = MULTIPLY(z11 - z13, FIX_1_414213562); /* 2*c4 */
     z5 = MULTIPLY(z10 + z12, FIX_1_847759065); /* 2*c2 */
     tmp10 = MULTIPLY(z12, FIX_1_082392200) - z5; /* 2*(c2-c6) */
     tmp12 = MULTIPLY(z10, - FIX_2_613125930) + z5; /* -2*(c2+c6) */
     tmp6 = tmp12 - tmp7;	/* phase 2 */
     tmp5 = tmp11 - tmp6;
     tmp4 = tmp10 + tmp5;
     wsptr[DCTSIZE*0] = (int) (tmp0 + tmp7);
     wsptr[DCTSIZE*7] = (int) (tmp0 - tmp7);
     wsptr[DCTSIZE*1] = (int) (tmp1 + tmp6);
     wsptr[DCTSIZE*6] = (int) (tmp1 - tmp6);
     wsptr[DCTSIZE*2] = (int) (tmp2 + tmp5);
     wsptr[DCTSIZE*5] = (int) (tmp2 - tmp5);
     wsptr[DCTSIZE*4] = (int) (tmp3 + tmp4);
     wsptr[DCTSIZE*3] = (int) (tmp3 - tmp4);
     inptr++;			/* advance pointers to next column */
     quantptr++;
     wsptr++;
   }
   /* Pass 2: process rows from work array, store into output array. */
   /* Note that we must descale the results by a factor of 8 == 2**3, */
   /* and also undo the PASS1_BITS scaling. */
   wsptr = workspace;
   for (ctr = 0; ctr < DCTSIZE; ctr++) {
     outptr = output_buf[ctr] + output_col;
     /* Rows of zeroes can be exploited in the same way as we did with columns.
      * However, the column calculation has created many nonzero AC terms, so
      * the simplification applies less often (typically 5% to 10% of the time).
      * On machines with very fast multiplication, it's possible that the
      * test takes more time than it's worth.  In that case this section
      * may be commented out.
      */
 #ifndef NO_ZERO_ROW_TEST
     if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 && wsptr[4] == 0 &&
 	wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) {
       /* AC terms all zero */
       JSAMPLE dcval = range_limit[IDESCALE(wsptr[0], PASS1_BITS+3)
 				  & RANGE_MASK];
       outptr[0] = dcval;
       outptr[1] = dcval;
       outptr[2] = dcval;
       outptr[3] = dcval;
       outptr[4] = dcval;
       outptr[5] = dcval;
       outptr[6] = dcval;
       outptr[7] = dcval;
       wsptr += DCTSIZE;		/* advance pointer to next row */
       continue;
     }
 #endif
     /* Even part */
     tmp10 = ((DCTELEM) wsptr[0] + (DCTELEM) wsptr[4]);
     tmp11 = ((DCTELEM) wsptr[0] - (DCTELEM) wsptr[4]);
     tmp13 = ((DCTELEM) wsptr[2] + (DCTELEM) wsptr[6]);
     tmp12 = MULTIPLY((DCTELEM) wsptr[2] - (DCTELEM) wsptr[6], FIX_1_414213562)
 	    - tmp13;
     tmp0 = tmp10 + tmp13;
     tmp3 = tmp10 - tmp13;
     tmp1 = tmp11 + tmp12;
     tmp2 = tmp11 - tmp12;
     /* Odd part */
     z13 = (DCTELEM) wsptr[5] + (DCTELEM) wsptr[3];
     z10 = (DCTELEM) wsptr[5] - (DCTELEM) wsptr[3];
     z11 = (DCTELEM) wsptr[1] + (DCTELEM) wsptr[7];
     z12 = (DCTELEM) wsptr[1] - (DCTELEM) wsptr[7];
     tmp7 = z11 + z13;		/* phase 5 */
     tmp11 = MULTIPLY(z11 - z13, FIX_1_414213562); /* 2*c4 */
     z5 = MULTIPLY(z10 + z12, FIX_1_847759065); /* 2*c2 */
     tmp10 = MULTIPLY(z12, FIX_1_082392200) - z5; /* 2*(c2-c6) */
     tmp12 = MULTIPLY(z10, - FIX_2_613125930) + z5; /* -2*(c2+c6) */
     tmp6 = tmp12 - tmp7;	/* phase 2 */
     tmp5 = tmp11 - tmp6;
     tmp4 = tmp10 + tmp5;
     /* Final output stage: scale down by a factor of 8 and range-limit */
     outptr[0] = range_limit[IDESCALE(tmp0 + tmp7, PASS1_BITS+3)
 			    & RANGE_MASK];
     outptr[7] = range_limit[IDESCALE(tmp0 - tmp7, PASS1_BITS+3)
 			    & RANGE_MASK];
     outptr[1] = range_limit[IDESCALE(tmp1 + tmp6, PASS1_BITS+3)
 			    & RANGE_MASK];
     outptr[6] = range_limit[IDESCALE(tmp1 - tmp6, PASS1_BITS+3)
 			    & RANGE_MASK];
     outptr[2] = range_limit[IDESCALE(tmp2 + tmp5, PASS1_BITS+3)
 			    & RANGE_MASK];
     outptr[5] = range_limit[IDESCALE(tmp2 - tmp5, PASS1_BITS+3)
 			    & RANGE_MASK];
     outptr[4] = range_limit[IDESCALE(tmp3 + tmp4, PASS1_BITS+3)
 			    & RANGE_MASK];
     outptr[3] = range_limit[IDESCALE(tmp3 - tmp4, PASS1_BITS+3)
 			    & RANGE_MASK];
     wsptr += DCTSIZE;		/* advance pointer to next row */
   }
 }
 #endif /* DCT_IFAST_SUPPORTED */

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media/libjpeg/jidctfst.c@b8a032363ba2 (annotated)

media/libjpeg/jidctfst.c