| /* |
| * IDCT implementation using the MIPS DSP ASE (little endian version) |
| * |
| * 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 |
| |
| |
| // this table of constants has been moved from mips_idct_le/_be.s to |
| // avoid having to make the assembler code position independent |
| static const int mips_idct_coefs[4] = { |
| 0x45464546, // FIX( 1.082392200 / 2) = 17734 = 0x4546 |
| 0x5A825A82, // FIX( 1.414213562 / 2) = 23170 = 0x5A82 |
| 0x76427642, // FIX( 1.847759065 / 2) = 30274 = 0x7642 |
| 0xAC61AC61 // FIX(-2.613125930 / 4) = -21407 = 0xAC61 |
| }; |
| |
| void mips_idct_columns(JCOEF * inptr, IFAST_MULT_TYPE * quantptr, |
| DCTELEM * wsptr, const int * mips_idct_coefs); |
| void mips_idct_rows(DCTELEM * wsptr, JSAMPARRAY output_buf, |
| JDIMENSION output_col, const int * mips_idct_coefs); |
| |
| |
| /* |
| * Perform dequantization and inverse DCT on one block of coefficients. |
| */ |
| |
| GLOBAL(void) |
| jpeg_idct_mips (j_decompress_ptr cinfo, jpeg_component_info * compptr, |
| JCOEFPTR coef_block, |
| JSAMPARRAY output_buf, JDIMENSION output_col) |
| { |
| JCOEFPTR inptr; |
| IFAST_MULT_TYPE * quantptr; |
| DCTELEM workspace[DCTSIZE2]; /* buffers data between passes */ |
| |
| /* Pass 1: process columns from input, store into work array. */ |
| |
| inptr = coef_block; |
| quantptr = (IFAST_MULT_TYPE *) compptr->dct_table; |
| |
| mips_idct_columns(inptr, quantptr, workspace, mips_idct_coefs); |
| |
| /* 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. */ |
| |
| mips_idct_rows(workspace, output_buf, output_col, mips_idct_coefs); |
| |
| } |
| |
| #endif /* DCT_IFAST_SUPPORTED */ |