You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
368 lines
13 KiB
368 lines
13 KiB
/* |
|
* 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 */
|
|
|