mirror of https://github.com/opencv/opencv.git
Open Source Computer Vision Library
https://opencv.org/
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.
224 lines
7.4 KiB
224 lines
7.4 KiB
/* |
|
* jfdctfst.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 |
|
* forward DCT (Discrete Cosine Transform). |
|
* |
|
* A 2-D DCT can be done by 1-D DCT on each row followed by 1-D DCT |
|
* on each column. 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 jfdctint.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. |
|
* |
|
* Again to save a few shifts, the intermediate results between pass 1 and |
|
* pass 2 are not upscaled, but are represented only to integral precision. |
|
* |
|
* 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). |
|
*/ |
|
|
|
#define CONST_BITS 8 |
|
|
|
|
|
/* 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_0_382683433 ((INT32) 98) /* FIX(0.382683433) */ |
|
#define FIX_0_541196100 ((INT32) 139) /* FIX(0.541196100) */ |
|
#define FIX_0_707106781 ((INT32) 181) /* FIX(0.707106781) */ |
|
#define FIX_1_306562965 ((INT32) 334) /* FIX(1.306562965) */ |
|
#else |
|
#define FIX_0_382683433 FIX(0.382683433) |
|
#define FIX_0_541196100 FIX(0.541196100) |
|
#define FIX_0_707106781 FIX(0.707106781) |
|
#define FIX_1_306562965 FIX(1.306562965) |
|
#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)) |
|
|
|
|
|
/* |
|
* Perform the forward DCT on one block of samples. |
|
*/ |
|
|
|
GLOBAL(void) |
|
jpeg_fdct_ifast (DCTELEM * data) |
|
{ |
|
DCTELEM tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7; |
|
DCTELEM tmp10, tmp11, tmp12, tmp13; |
|
DCTELEM z1, z2, z3, z4, z5, z11, z13; |
|
DCTELEM *dataptr; |
|
int ctr; |
|
SHIFT_TEMPS |
|
|
|
/* Pass 1: process rows. */ |
|
|
|
dataptr = data; |
|
for (ctr = DCTSIZE-1; ctr >= 0; ctr--) { |
|
tmp0 = dataptr[0] + dataptr[7]; |
|
tmp7 = dataptr[0] - dataptr[7]; |
|
tmp1 = dataptr[1] + dataptr[6]; |
|
tmp6 = dataptr[1] - dataptr[6]; |
|
tmp2 = dataptr[2] + dataptr[5]; |
|
tmp5 = dataptr[2] - dataptr[5]; |
|
tmp3 = dataptr[3] + dataptr[4]; |
|
tmp4 = dataptr[3] - dataptr[4]; |
|
|
|
/* Even part */ |
|
|
|
tmp10 = tmp0 + tmp3; /* phase 2 */ |
|
tmp13 = tmp0 - tmp3; |
|
tmp11 = tmp1 + tmp2; |
|
tmp12 = tmp1 - tmp2; |
|
|
|
dataptr[0] = tmp10 + tmp11; /* phase 3 */ |
|
dataptr[4] = tmp10 - tmp11; |
|
|
|
z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781); /* c4 */ |
|
dataptr[2] = tmp13 + z1; /* phase 5 */ |
|
dataptr[6] = tmp13 - z1; |
|
|
|
/* Odd part */ |
|
|
|
tmp10 = tmp4 + tmp5; /* phase 2 */ |
|
tmp11 = tmp5 + tmp6; |
|
tmp12 = tmp6 + tmp7; |
|
|
|
/* The rotator is modified from fig 4-8 to avoid extra negations. */ |
|
z5 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */ |
|
z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5; /* c2-c6 */ |
|
z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5; /* c2+c6 */ |
|
z3 = MULTIPLY(tmp11, FIX_0_707106781); /* c4 */ |
|
|
|
z11 = tmp7 + z3; /* phase 5 */ |
|
z13 = tmp7 - z3; |
|
|
|
dataptr[5] = z13 + z2; /* phase 6 */ |
|
dataptr[3] = z13 - z2; |
|
dataptr[1] = z11 + z4; |
|
dataptr[7] = z11 - z4; |
|
|
|
dataptr += DCTSIZE; /* advance pointer to next row */ |
|
} |
|
|
|
/* Pass 2: process columns. */ |
|
|
|
dataptr = data; |
|
for (ctr = DCTSIZE-1; ctr >= 0; ctr--) { |
|
tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7]; |
|
tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7]; |
|
tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6]; |
|
tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6]; |
|
tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5]; |
|
tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5]; |
|
tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4]; |
|
tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4]; |
|
|
|
/* Even part */ |
|
|
|
tmp10 = tmp0 + tmp3; /* phase 2 */ |
|
tmp13 = tmp0 - tmp3; |
|
tmp11 = tmp1 + tmp2; |
|
tmp12 = tmp1 - tmp2; |
|
|
|
dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */ |
|
dataptr[DCTSIZE*4] = tmp10 - tmp11; |
|
|
|
z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781); /* c4 */ |
|
dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */ |
|
dataptr[DCTSIZE*6] = tmp13 - z1; |
|
|
|
/* Odd part */ |
|
|
|
tmp10 = tmp4 + tmp5; /* phase 2 */ |
|
tmp11 = tmp5 + tmp6; |
|
tmp12 = tmp6 + tmp7; |
|
|
|
/* The rotator is modified from fig 4-8 to avoid extra negations. */ |
|
z5 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */ |
|
z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5; /* c2-c6 */ |
|
z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5; /* c2+c6 */ |
|
z3 = MULTIPLY(tmp11, FIX_0_707106781); /* c4 */ |
|
|
|
z11 = tmp7 + z3; /* phase 5 */ |
|
z13 = tmp7 - z3; |
|
|
|
dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */ |
|
dataptr[DCTSIZE*3] = z13 - z2; |
|
dataptr[DCTSIZE*1] = z11 + z4; |
|
dataptr[DCTSIZE*7] = z11 - z4; |
|
|
|
dataptr++; /* advance pointer to next column */ |
|
} |
|
} |
|
|
|
#endif /* DCT_IFAST_SUPPORTED */
|
|
|