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Diffstat (limited to 'src/jpeg-6/jidctfst.c')
| -rw-r--r-- | src/jpeg-6/jidctfst.c | 367 |
1 files changed, 367 insertions, 0 deletions
diff --git a/src/jpeg-6/jidctfst.c b/src/jpeg-6/jidctfst.c new file mode 100644 index 0000000..5736817 --- /dev/null +++ b/src/jpeg-6/jidctfst.c @@ -0,0 +1,367 @@ +/* + * jidctfst.c + * + * Copyright (C) 1994-1995, 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] | inptr[DCTSIZE*2] | inptr[DCTSIZE*3] | + inptr[DCTSIZE*4] | inptr[DCTSIZE*5] | inptr[DCTSIZE*6] | + 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] | wsptr[2] | wsptr[3] | wsptr[4] | wsptr[5] | wsptr[6] | + 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 */ |