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doom3-bfg/neo/renderer/jpeg-6/jidctfst.cpp
Brian Harris 5016f605b8 Initial commit
2012-11-26 12:58:24 -06:00

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/*
* jidctfst.c
*
* Copyright (C) 1994-1995, 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 8 x8 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] | inptr[DCTSIZE * 2] | inptr[DCTSIZE * 3] |
inptr[DCTSIZE * 4] | inptr[DCTSIZE * 5] | inptr[DCTSIZE * 6] |
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] | wsptr[2] | wsptr[3] | wsptr[4] | wsptr[5] | wsptr[6] |
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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