Source code of Windows XP (NT5)
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#include "stdafx.h"
#pragma hdrstop
/***************************************************************************
*
* INTEL Corporation Proprietary Information
*
*
* Copyright (c) 1996 Intel Corporation.
* All rights reserved.
*
***************************************************************************
*/
/*
* jidctfst.c
*
* Copyright (C) 1994-1996, 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
//#define DESCALE(x,n) RIGHT_SHIFT((x) + (ONE << ((n)-1)), n)
/* 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))
#define MULTIPLY(var,const) ((DCTELEM) ((var) * (const)))
/* 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))
#define DEQUANTIZE(coef,quantval) (((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
static const long x5a825a825a825a82 = 0x0000016a ;
static const long x539f539f539f539f = 0xfffffd63 ;
static const long x4546454645464546 = 0x00000115 ;
static const long x61f861f861f861f8 = 0x000001d9 ;
/*
* Perform dequantization and inverse DCT on one block of coefficients.
*/
GLOBAL(void)
pidct8x8aan (JCOEFPTR coef_block, short * wsptr, short * quantptr,
JSAMPARRAY output_buf, JDIMENSION output_col, JSAMPLE *range_limit )
{
INT32 locdwinptr, locdwqptr, locdwwsptr, locwctr ;
short locwcounter, locwtmp0, locwtmp1 ;
short locwtmp3, scratch1, scratch2, scratch3 ;
// do the 2-Dal idct and store the corresponding results
// from the range_limit array
// pidct(coef_block, quantptr, wsptr, output_buf, output_col, range_limit) ;
__asm {
mov esi, coef_block ; source coeff
mov edi, quantptr ; quant pointer
mov locdwinptr, esi
mov eax, wsptr ; temp storage pointer
mov locdwqptr, edi
mov locdwwsptr, eax
mov locwcounter, 8
;; perform the 1D-idct on each of the eight columns
idct_column:
mov esi, locdwinptr
mov edi, locdwqptr
mov ax, word ptr [esi+16*0]
mov bx, word ptr [esi+16*4]
imul ax, word ptr [edi+16*0]
mov cx, word ptr [esi+16*2]
imul bx, word ptr [edi+16*4]
mov dx, word ptr [esi+16*6]
imul cx, word ptr [edi+16*2]
imul dx, word ptr [edi+16*6]
;;;; at this point C0, C2, C4 and C6 have been dequantized
mov scratch1, ax
add ax, bx ; tmp10 in ax
sub scratch1, bx ; tmp11
mov bx, cx
add cx, dx ; tmp13 in cx
sub bx, dx ; tmp1 - tmp3 in bx
mov dx, ax
movsx ebx, bx ; sign extend bx: get ready to do imul
add ax, cx ; tmp0 in ax
imul ebx, dword ptr x5a825a825a825a82
sub dx, cx ; tmp3 in dx
mov locwtmp0, ax
mov locwtmp3, dx
sar ebx, 8 ; bx now has (tmp1-tmp3)*1.414
mov ax, scratch1 ; copy of tmp11
sub bx, cx ; tmp12 in bx
add ax, bx ; tmp1 in ax
sub scratch1, bx ; tmp2
mov locwtmp1, ax
;;;;;completed computing/storing the even part;;;;;;;;;;
mov ax, [esi+16*1] ; get C1
imul ax, [edi+16*1]
mov bx, [esi+16*7] ; get C7
mov cx, [esi+16*3]
imul bx, [edi+16*7]
mov dx, [esi+16*5]
imul cx, [edi+16*3]
imul dx, [edi+16*5]
mov scratch2, ax
add ax, bx ; z11 in ax
sub scratch2, bx ; z12
mov bx, dx ; copy of deQ C5
add dx, cx ; z13 in dx
sub bx, cx ; z10 in bx
mov cx, ax ; copy of z11
add ax, dx ; tmp7 in ax
sub cx, dx ; partial tmp11
movsx ecx, cx
mov dx, bx ; copy of z10
add bx, scratch2 ; partial z5
imul ecx, dword ptr x5a825a825a825a82
movsx edx, dx ; sign extend z10: get ready for imul
movsx ebx, bx ; sign extend partial z5 for imul
imul edx, dword ptr x539f539f539f539f ; partial tmp12
imul ebx, dword ptr x61f861f861f861f8 ; partial z5 product
mov di, scratch2
movsx edi, di ; sign extend z12: get ready for imul
sar ecx, 8 ; tmp11 in cx
sar ebx, 8 ; z5 in bx
imul edi, dword ptr x4546454645464546
sar edx, 8
sar edi, 8
sub di, bx ; tmp10
add dx, bx ; tmp12 in dx
sub dx, ax ; tmp6 in dx
sub cx, dx ; tmp5 in cx
add di, cx ; tmp4
mov scratch3, di
;;; completed calculating the odd part ;;;;;;;;;;;
mov edi, dword ptr locdwwsptr ; get address of temp. destn
mov si, ax ; copy of tmp7
mov bx, locwtmp0 ; get tmp0
add ax, locwtmp0 ; wsptr[0]
sub bx, si ; wsptr[7]
mov word ptr [edi+16*0], ax
mov word ptr [edi+16*7], bx
mov ax, dx ; copy of tmp6
mov bx, locwtmp1
add dx, bx ; wsptr[1]
sub bx, ax ; wsptr[6]
mov word ptr [edi+16*1], dx
mov word ptr [edi+16*6], bx
mov dx, cx ; copy of tmp5
mov bx, scratch1
add cx, bx ; wsptr[2]
sub bx, dx ; wsptr[5]
mov word ptr [edi+16*2], cx
mov word ptr [edi+16*5], bx
mov cx, scratch3 ; copy of tmp4
mov ax, locwtmp3
add scratch3, ax ; wsptr[4]
sub ax, cx ; wsptr[3]
mov bx, scratch3
mov word ptr [edi+16*4], bx
mov word ptr [edi+16*3], ax
;;;;; completed storing 1D idct of one column ;;;;;;;;
;; update inptr, qptr and wsptr for next column
add locdwinptr, 2
add locdwqptr, 2
add locdwwsptr, 2
mov ax, locwcounter ; get loop count
dec ax ; another loop done
mov locwcounter, ax
jnz idct_column
;;;;;;; end of 1D idct on all columns ;;;;;;;
;;;;;;; temp result is stored in wsptr ;;;;;;;
;;;;;;; perform 1D-idct on each row and store final result
mov esi, wsptr ; initialize source ptr to original wsptr
mov locwctr, 0
mov locwcounter, 8
mov locdwwsptr, esi
idct_row:
mov edi, output_buf
mov esi, locdwwsptr
add edi, locwctr
mov edi, [edi] ; get output_buf[ctr]
add edi, output_col ; now edi is pointing to the resp. row
add locwctr, 4
;; get even coeffs. and do the even part
mov ax, word ptr [esi+2*0]
mov bx, word ptr [esi+2*4]
mov cx, word ptr [esi+2*2]
mov dx, word ptr [esi+2*6]
mov scratch1, ax
add ax, bx ; tmp10 in ax
sub scratch1, bx ; tmp11
mov bx, cx
add cx, dx ; tmp13 in cx
sub bx, dx ; tmp1 - tmp3 in bx
mov dx, ax
movsx ebx, bx ; sign extend bx: get ready to do imul
add ax, cx ; tmp0 in ax
imul ebx, dword ptr x5a825a825a825a82
sub dx, cx ; tmp3 in dx
mov locwtmp0, ax
mov locwtmp3, dx
sar ebx, 8 ; bx now has (tmp1-tmp3)*1.414
mov ax, scratch1 ; copy of tmp11
sub bx, cx ; tmp12 in bx
add ax, bx ; tmp1 in ax
sub scratch1, bx ; tmp2
mov locwtmp1, ax
;;;;;completed computing/storing the even part;;;;;;;;;;
mov ax, [esi+2*1] ; get C1
mov bx, [esi+2*7] ; get C7
mov cx, [esi+2*3]
mov dx, [esi+2*5]
mov scratch2, ax
add ax, bx ; z11 in ax
sub scratch2, bx ; z12
mov bx, dx ; copy of deQ C5
add dx, cx ; z13 in dx
sub bx, cx ; z10 in bx
mov cx, ax ; copy of z11
add ax, dx ; tmp7 in ax
sub cx, dx ; partial tmp11
movsx ecx, cx
mov dx, bx ; copy of z10
add bx, scratch2 ; partial z5
imul ecx, dword ptr x5a825a825a825a82
movsx edx, dx ; sign extend z10: get ready for imul
movsx ebx, bx ; sign extend partial z5 for imul
imul edx, dword ptr x539f539f539f539f ; partial tmp12
imul ebx, dword ptr x61f861f861f861f8 ; partial z5 product
mov si, scratch2
movsx esi, si ; sign extend z12: get ready for imul
sar ecx, 8 ; tmp11 in cx
sar ebx, 8 ; z5 in bx
imul esi, dword ptr x4546454645464546
sar edx, 8
sar esi, 8
sub si, bx ; tmp10
add dx, bx ; tmp12 in dx
sub dx, ax ; tmp6 in dx
sub cx, dx ; tmp5 in cx
add si, cx ; tmp4
mov scratch3, si
;;; completed calculating the odd part ;;;;;;;;;;;
mov si, ax ; copy of tmp7
mov bx, locwtmp0 ; get tmp0
add ax, locwtmp0 ; wsptr[0]
sub bx, si ; wsptr[7]
mov esi, range_limit ; initialize esi to range_limit pointer
sar ax, 5
sar bx, 5
and eax, 3ffh
and ebx, 3ffh
mov al, byte ptr [esi][eax]
mov bl, byte ptr [esi][ebx]
mov byte ptr [edi+0], al
mov byte ptr [edi+7], bl
mov ax, dx ; copy of tmp6
mov bx, locwtmp1
add dx, bx ; wsptr[1]
sub bx, ax ; wsptr[6]
sar dx, 5
sar bx, 5
and edx, 3ffh
and ebx, 3ffh
mov dl, byte ptr [esi][edx]
mov bl, byte ptr [esi][ebx]
mov byte ptr [edi+1], dl
mov byte ptr [edi+6], bl
mov dx, cx ; copy of tmp5
mov bx, scratch1
add cx, bx ; wsptr[2]
sub bx, dx ; wsptr[5]
sar cx, 5
sar bx, 5
and ecx, 3ffh
and ebx, 3ffh
mov cl, byte ptr [esi][ecx]
mov bl, byte ptr [esi][ebx]
mov byte ptr [edi+2], cl
mov byte ptr [edi+5], bl
mov cx, scratch3 ; copy of tmp4
mov ax, locwtmp3
add scratch3, ax ; wsptr[4]
sub ax, cx ; wsptr[3]
sar scratch3, 5
sar ax, 5
mov cx, scratch3
and ecx, 3ffh
and eax, 3ffh
mov bl, byte ptr [esi][ecx]
mov al, byte ptr [esi][eax]
mov byte ptr [edi+4], bl
mov byte ptr [edi+3], al
;;;;; completed storing 1D idct of one row ;;;;;;;;
;; update the source pointer (wsptr) for next row
add locdwwsptr, 16
mov ax, locwcounter ; get loop count
dec ax ; another loop done
mov locwcounter, ax
jnz idct_row
;; end of 1D idct on all rows
;; final result is stored in outptr
} /* end of __asm */
}
#endif /* DCT_IFAST_SUPPORTED */