JIDCTRED.c
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上传日期:2022-05-11
资源大小:5032k
文件大小:14k
源码类别:
网络截获/分析
开发平台:
Visual C++
- ////////////////////////////////////////////////////////////////////////
- //
- // Note : this file is included as part of the Smaller Animals Software
- // JpegFile package. Though this file has not been modified from it's
- // original IJG 6a form, it is not the responsibility on the Independent
- // JPEG Group to answer questions regarding this code.
- //
- // Any questions you have about this code should be addressed to :
- //
- // CHRISDL@PAGESZ.NET - the distributor of this package.
- //
- // Remember, by including this code in the JpegFile package, Smaller
- // Animals Software assumes all responsibilities for answering questions
- // about it. If we (SA Software) can't answer your questions ourselves, we
- // will direct you to people who can.
- //
- // Thanks, CDL.
- //
- ////////////////////////////////////////////////////////////////////////
- /*
- * jidctred.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 inverse-DCT routines that produce reduced-size output:
- * either 4x4, 2x2, or 1x1 pixels from an 8x8 DCT block.
- *
- * The implementation is based on the Loeffler, Ligtenberg and Moschytz (LL&M)
- * algorithm used in jidctint.c. We simply replace each 8-to-8 1-D IDCT step
- * with an 8-to-4 step that produces the four averages of two adjacent outputs
- * (or an 8-to-2 step producing two averages of four outputs, for 2x2 output).
- * These steps were derived by computing the corresponding values at the end
- * of the normal LL&M code, then simplifying as much as possible.
- *
- * 1x1 is trivial: just take the DC coefficient divided by 8.
- *
- * See jidctint.c for additional comments.
- */
- #define JPEG_INTERNALS
- #include "jinclude.h"
- #include "jpeglib.h"
- #include "jdct.h" /* Private declarations for DCT subsystem */
- #ifdef IDCT_SCALING_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 is the same as in jidctint.c. */
- #if BITS_IN_JSAMPLE == 8
- #define CONST_BITS 13
- #define PASS1_BITS 2
- #else
- #define CONST_BITS 13
- #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 == 13
- #define FIX_0_211164243 ((long) 1730) /* FIX(0.211164243) */
- #define FIX_0_509795579 ((long) 4176) /* FIX(0.509795579) */
- #define FIX_0_601344887 ((long) 4926) /* FIX(0.601344887) */
- #define FIX_0_720959822 ((long) 5906) /* FIX(0.720959822) */
- #define FIX_0_765366865 ((long) 6270) /* FIX(0.765366865) */
- #define FIX_0_850430095 ((long) 6967) /* FIX(0.850430095) */
- #define FIX_0_899976223 ((long) 7373) /* FIX(0.899976223) */
- #define FIX_1_061594337 ((long) 8697) /* FIX(1.061594337) */
- #define FIX_1_272758580 ((long) 10426) /* FIX(1.272758580) */
- #define FIX_1_451774981 ((long) 11893) /* FIX(1.451774981) */
- #define FIX_1_847759065 ((long) 15137) /* FIX(1.847759065) */
- #define FIX_2_172734803 ((long) 17799) /* FIX(2.172734803) */
- #define FIX_2_562915447 ((long) 20995) /* FIX(2.562915447) */
- #define FIX_3_624509785 ((long) 29692) /* FIX(3.624509785) */
- #else
- #define FIX_0_211164243 FIX(0.211164243)
- #define FIX_0_509795579 FIX(0.509795579)
- #define FIX_0_601344887 FIX(0.601344887)
- #define FIX_0_720959822 FIX(0.720959822)
- #define FIX_0_765366865 FIX(0.765366865)
- #define FIX_0_850430095 FIX(0.850430095)
- #define FIX_0_899976223 FIX(0.899976223)
- #define FIX_1_061594337 FIX(1.061594337)
- #define FIX_1_272758580 FIX(1.272758580)
- #define FIX_1_451774981 FIX(1.451774981)
- #define FIX_1_847759065 FIX(1.847759065)
- #define FIX_2_172734803 FIX(2.172734803)
- #define FIX_2_562915447 FIX(2.562915447)
- #define FIX_3_624509785 FIX(3.624509785)
- #endif
- /* Multiply an long variable by an long constant to yield an long result.
- * For 8-bit samples with the recommended scaling, all the variable
- * and constant values involved are no more than 16 bits wide, so a
- * 16x16->32 bit multiply can be used instead of a full 32x32 multiply.
- * For 12-bit samples, a full 32-bit multiplication will be needed.
- */
- #if BITS_IN_JSAMPLE == 8
- #define MULTIPLY(var,const) MULTIPLY16C16(var,const)
- #else
- #define MULTIPLY(var,const) ((var) * (const))
- #endif
- /* Dequantize a coefficient by multiplying it by the multiplier-table
- * entry; produce an int result. In this module, both inputs and result
- * are 16 bits or less, so either int or short multiply will work.
- */
- #define DEQUANTIZE(coef,quantval) (((ISLOW_MULT_TYPE) (coef)) * (quantval))
- /*
- * Perform dequantization and inverse DCT on one block of coefficients,
- * producing a reduced-size 4x4 output block.
- */
- GLOBAL(void)
- jpeg_idct_4x4 (j_decompress_ptr cinfo, jpeg_component_info * compptr,
- JCOEFPTR coef_block,
- JSAMPARRAY output_buf, JDIMENSION output_col)
- {
- long tmp0, tmp2, tmp10, tmp12;
- long z1, z2, z3, z4;
- JCOEFPTR inptr;
- ISLOW_MULT_TYPE * quantptr;
- int * wsptr;
- JSAMPROW outptr;
- JSAMPLE *range_limit = IDCT_range_limit(cinfo);
- int ctr;
- int workspace[DCTSIZE*4]; /* buffers data between passes */
- SHIFT_TEMPS
- /* Pass 1: process columns from input, store into work array. */
- inptr = coef_block;
- quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
- wsptr = workspace;
- for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) {
- /* Don't bother to process column 4, because second pass won't use it */
- if (ctr == DCTSIZE-4)
- continue;
- if ((inptr[DCTSIZE*1] | inptr[DCTSIZE*2] | inptr[DCTSIZE*3] |
- inptr[DCTSIZE*5] | inptr[DCTSIZE*6] | inptr[DCTSIZE*7]) == 0) {
- /* AC terms all zero; we need not examine term 4 for 4x4 output */
- int dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]) << PASS1_BITS;
- wsptr[DCTSIZE*0] = dcval;
- wsptr[DCTSIZE*1] = dcval;
- wsptr[DCTSIZE*2] = dcval;
- wsptr[DCTSIZE*3] = dcval;
- continue;
- }
- /* Even part */
- tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
- tmp0 <<= (CONST_BITS+1);
- z2 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]);
- z3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]);
- tmp2 = MULTIPLY(z2, FIX_1_847759065) + MULTIPLY(z3, - FIX_0_765366865);
- tmp10 = tmp0 + tmp2;
- tmp12 = tmp0 - tmp2;
- /* Odd part */
- z1 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
- z2 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
- z3 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
- z4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
- tmp0 = MULTIPLY(z1, - FIX_0_211164243) /* sqrt(2) * (c3-c1) */
- + MULTIPLY(z2, FIX_1_451774981) /* sqrt(2) * (c3+c7) */
- + MULTIPLY(z3, - FIX_2_172734803) /* sqrt(2) * (-c1-c5) */
- + MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * (c5+c7) */
- tmp2 = MULTIPLY(z1, - FIX_0_509795579) /* sqrt(2) * (c7-c5) */
- + MULTIPLY(z2, - FIX_0_601344887) /* sqrt(2) * (c5-c1) */
- + MULTIPLY(z3, FIX_0_899976223) /* sqrt(2) * (c3-c7) */
- + MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */
- /* Final output stage */
- wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp2, CONST_BITS-PASS1_BITS+1);
- wsptr[DCTSIZE*3] = (int) DESCALE(tmp10 - tmp2, CONST_BITS-PASS1_BITS+1);
- wsptr[DCTSIZE*1] = (int) DESCALE(tmp12 + tmp0, CONST_BITS-PASS1_BITS+1);
- wsptr[DCTSIZE*2] = (int) DESCALE(tmp12 - tmp0, CONST_BITS-PASS1_BITS+1);
- }
- /* Pass 2: process 4 rows from work array, store into output array. */
- wsptr = workspace;
- for (ctr = 0; ctr < 4; ctr++) {
- outptr = output_buf[ctr] + output_col;
- /* It's not clear whether a zero row test is worthwhile here ... */
- #ifndef NO_ZERO_ROW_TEST
- if ((wsptr[1] | wsptr[2] | wsptr[3] | wsptr[5] | wsptr[6] |
- wsptr[7]) == 0) {
- /* AC terms all zero */
- JSAMPLE dcval = range_limit[(int) DESCALE((long) wsptr[0], PASS1_BITS+3)
- & RANGE_MASK];
- outptr[0] = dcval;
- outptr[1] = dcval;
- outptr[2] = dcval;
- outptr[3] = dcval;
- wsptr += DCTSIZE; /* advance pointer to next row */
- continue;
- }
- #endif
- /* Even part */
- tmp0 = ((long) wsptr[0]) << (CONST_BITS+1);
- tmp2 = MULTIPLY((long) wsptr[2], FIX_1_847759065)
- + MULTIPLY((long) wsptr[6], - FIX_0_765366865);
- tmp10 = tmp0 + tmp2;
- tmp12 = tmp0 - tmp2;
- /* Odd part */
- z1 = (long) wsptr[7];
- z2 = (long) wsptr[5];
- z3 = (long) wsptr[3];
- z4 = (long) wsptr[1];
- tmp0 = MULTIPLY(z1, - FIX_0_211164243) /* sqrt(2) * (c3-c1) */
- + MULTIPLY(z2, FIX_1_451774981) /* sqrt(2) * (c3+c7) */
- + MULTIPLY(z3, - FIX_2_172734803) /* sqrt(2) * (-c1-c5) */
- + MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * (c5+c7) */
- tmp2 = MULTIPLY(z1, - FIX_0_509795579) /* sqrt(2) * (c7-c5) */
- + MULTIPLY(z2, - FIX_0_601344887) /* sqrt(2) * (c5-c1) */
- + MULTIPLY(z3, FIX_0_899976223) /* sqrt(2) * (c3-c7) */
- + MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */
- /* Final output stage */
- outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp2,
- CONST_BITS+PASS1_BITS+3+1)
- & RANGE_MASK];
- outptr[3] = range_limit[(int) DESCALE(tmp10 - tmp2,
- CONST_BITS+PASS1_BITS+3+1)
- & RANGE_MASK];
- outptr[1] = range_limit[(int) DESCALE(tmp12 + tmp0,
- CONST_BITS+PASS1_BITS+3+1)
- & RANGE_MASK];
- outptr[2] = range_limit[(int) DESCALE(tmp12 - tmp0,
- CONST_BITS+PASS1_BITS+3+1)
- & RANGE_MASK];
- wsptr += DCTSIZE; /* advance pointer to next row */
- }
- }
- /*
- * Perform dequantization and inverse DCT on one block of coefficients,
- * producing a reduced-size 2x2 output block.
- */
- GLOBAL(void)
- jpeg_idct_2x2 (j_decompress_ptr cinfo, jpeg_component_info * compptr,
- JCOEFPTR coef_block,
- JSAMPARRAY output_buf, JDIMENSION output_col)
- {
- long tmp0, tmp10, z1;
- JCOEFPTR inptr;
- ISLOW_MULT_TYPE * quantptr;
- int * wsptr;
- JSAMPROW outptr;
- JSAMPLE *range_limit = IDCT_range_limit(cinfo);
- int ctr;
- int workspace[DCTSIZE*2]; /* buffers data between passes */
- SHIFT_TEMPS
- /* Pass 1: process columns from input, store into work array. */
- inptr = coef_block;
- quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
- wsptr = workspace;
- for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) {
- /* Don't bother to process columns 2,4,6 */
- if (ctr == DCTSIZE-2 || ctr == DCTSIZE-4 || ctr == DCTSIZE-6)
- continue;
- if ((inptr[DCTSIZE*1] | inptr[DCTSIZE*3] |
- inptr[DCTSIZE*5] | inptr[DCTSIZE*7]) == 0) {
- /* AC terms all zero; we need not examine terms 2,4,6 for 2x2 output */
- int dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]) << PASS1_BITS;
- wsptr[DCTSIZE*0] = dcval;
- wsptr[DCTSIZE*1] = dcval;
- continue;
- }
- /* Even part */
- z1 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
- tmp10 = z1 << (CONST_BITS+2);
- /* Odd part */
- z1 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
- tmp0 = MULTIPLY(z1, - FIX_0_720959822); /* sqrt(2) * (c7-c5+c3-c1) */
- z1 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
- tmp0 += MULTIPLY(z1, FIX_0_850430095); /* sqrt(2) * (-c1+c3+c5+c7) */
- z1 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
- tmp0 += MULTIPLY(z1, - FIX_1_272758580); /* sqrt(2) * (-c1+c3-c5-c7) */
- z1 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
- tmp0 += MULTIPLY(z1, FIX_3_624509785); /* sqrt(2) * (c1+c3+c5+c7) */
- /* Final output stage */
- wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp0, CONST_BITS-PASS1_BITS+2);
- wsptr[DCTSIZE*1] = (int) DESCALE(tmp10 - tmp0, CONST_BITS-PASS1_BITS+2);
- }
- /* Pass 2: process 2 rows from work array, store into output array. */
- wsptr = workspace;
- for (ctr = 0; ctr < 2; ctr++) {
- outptr = output_buf[ctr] + output_col;
- /* It's not clear whether a zero row test is worthwhile here ... */
- #ifndef NO_ZERO_ROW_TEST
- if ((wsptr[1] | wsptr[3] | wsptr[5] | wsptr[7]) == 0) {
- /* AC terms all zero */
- JSAMPLE dcval = range_limit[(int) DESCALE((long) wsptr[0], PASS1_BITS+3)
- & RANGE_MASK];
- outptr[0] = dcval;
- outptr[1] = dcval;
- wsptr += DCTSIZE; /* advance pointer to next row */
- continue;
- }
- #endif
- /* Even part */
- tmp10 = ((long) wsptr[0]) << (CONST_BITS+2);
- /* Odd part */
- tmp0 = MULTIPLY((long) wsptr[7], - FIX_0_720959822) /* sqrt(2) * (c7-c5+c3-c1) */
- + MULTIPLY((long) wsptr[5], FIX_0_850430095) /* sqrt(2) * (-c1+c3+c5+c7) */
- + MULTIPLY((long) wsptr[3], - FIX_1_272758580) /* sqrt(2) * (-c1+c3-c5-c7) */
- + MULTIPLY((long) wsptr[1], FIX_3_624509785); /* sqrt(2) * (c1+c3+c5+c7) */
- /* Final output stage */
- outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp0,
- CONST_BITS+PASS1_BITS+3+2)
- & RANGE_MASK];
- outptr[1] = range_limit[(int) DESCALE(tmp10 - tmp0,
- CONST_BITS+PASS1_BITS+3+2)
- & RANGE_MASK];
- wsptr += DCTSIZE; /* advance pointer to next row */
- }
- }
- /*
- * Perform dequantization and inverse DCT on one block of coefficients,
- * producing a reduced-size 1x1 output block.
- */
- GLOBAL(void)
- jpeg_idct_1x1 (j_decompress_ptr cinfo, jpeg_component_info * compptr,
- JCOEFPTR coef_block,
- JSAMPARRAY output_buf, JDIMENSION output_col)
- {
- int dcval;
- ISLOW_MULT_TYPE * quantptr;
- JSAMPLE *range_limit = IDCT_range_limit(cinfo);
- SHIFT_TEMPS
- /* We hardly need an inverse DCT routine for this: just take the
- * average pixel value, which is one-eighth of the DC coefficient.
- */
- quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
- dcval = DEQUANTIZE(coef_block[0], quantptr[0]);
- dcval = (int) DESCALE((long) dcval, 3);
- output_buf[0][output_col] = range_limit[dcval & RANGE_MASK];
- }
- #endif /* IDCT_SCALING_SUPPORTED */