| /* |
| * jidctfst.c |
| * |
| * This file was part of the Independent JPEG Group's software: |
| * Copyright (C) 1994-1998, Thomas G. Lane. |
| * libjpeg-turbo Modifications: |
| * Copyright (C) 2015, D. R. Commander. |
| * For conditions of distribution and use, see the accompanying README.ijg |
| * 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.ijg). 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 ((JLONG)277) /* FIX(1.082392200) */ |
| #define FIX_1_414213562 ((JLONG)362) /* FIX(1.414213562) */ |
| #define FIX_1_847759065 ((JLONG)473) /* FIX(1.847759065) */ |
| #define FIX_2_613125930 ((JLONG)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 JLONG 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 JLONG, 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 JLONG 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 */ |
