#if !defined(_FX_JPEG_TURBO_) | |
/* | |
* 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 */ | |
#endif //_FX_JPEG_TURBO_ |