| /* |
| * jidctflt.c |
| * |
| * This file was part of the Independent JPEG Group's software: |
| * Copyright (C) 1994-1998, Thomas G. Lane. |
| * Modified 2010 by Guido Vollbeding. |
| * libjpeg-turbo Modifications: |
| * Copyright (C) 2014, 2022, D. R. Commander. |
| * For conditions of distribution and use, see the accompanying README.ijg |
| * file. |
| * |
| * This file contains a floating-point implementation of the |
| * inverse DCT (Discrete Cosine Transform). In the IJG code, this routine |
| * must also perform dequantization of the input coefficients. |
| * |
| * This implementation should be more accurate than either of the integer |
| * IDCT implementations. However, it may not give the same results on all |
| * machines because of differences in roundoff behavior. Speed will depend |
| * on the hardware's floating point capacity. |
| * |
| * 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 a fixed-point |
| * implementation, accuracy is lost due to imprecise representation of the |
| * scaled quantization values. However, that problem does not arise if |
| * we use floating point arithmetic. |
| */ |
| |
| #define JPEG_INTERNALS |
| #include "jinclude.h" |
| #include "jpeglib.h" |
| #include "jdct.h" /* Private declarations for DCT subsystem */ |
| |
| #ifdef DCT_FLOAT_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 |
| |
| |
| /* Dequantize a coefficient by multiplying it by the multiplier-table |
| * entry; produce a float result. |
| */ |
| |
| #define DEQUANTIZE(coef, quantval) (((FAST_FLOAT)(coef)) * (quantval)) |
| |
| |
| /* |
| * Perform dequantization and inverse DCT on one block of coefficients. |
| */ |
| |
| GLOBAL(void) |
| _jpeg_idct_float(j_decompress_ptr cinfo, jpeg_component_info *compptr, |
| JCOEFPTR coef_block, _JSAMPARRAY output_buf, |
| JDIMENSION output_col) |
| { |
| FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7; |
| FAST_FLOAT tmp10, tmp11, tmp12, tmp13; |
| FAST_FLOAT z5, z10, z11, z12, z13; |
| JCOEFPTR inptr; |
| FLOAT_MULT_TYPE *quantptr; |
| FAST_FLOAT *wsptr; |
| _JSAMPROW outptr; |
| _JSAMPLE *range_limit = (_JSAMPLE *)cinfo->sample_range_limit; |
| int ctr; |
| FAST_FLOAT workspace[DCTSIZE2]; /* buffers data between passes */ |
| #define _0_125 ((FLOAT_MULT_TYPE)0.125) |
| |
| /* Pass 1: process columns from input, store into work array. */ |
| |
| inptr = coef_block; |
| quantptr = (FLOAT_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 */ |
| FAST_FLOAT dcval = DEQUANTIZE(inptr[DCTSIZE * 0], |
| quantptr[DCTSIZE * 0] * _0_125); |
| |
| 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] * _0_125); |
| tmp1 = DEQUANTIZE(inptr[DCTSIZE * 2], quantptr[DCTSIZE * 2] * _0_125); |
| tmp2 = DEQUANTIZE(inptr[DCTSIZE * 4], quantptr[DCTSIZE * 4] * _0_125); |
| tmp3 = DEQUANTIZE(inptr[DCTSIZE * 6], quantptr[DCTSIZE * 6] * _0_125); |
| |
| tmp10 = tmp0 + tmp2; /* phase 3 */ |
| tmp11 = tmp0 - tmp2; |
| |
| tmp13 = tmp1 + tmp3; /* phases 5-3 */ |
| tmp12 = (tmp1 - tmp3) * ((FAST_FLOAT)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] * _0_125); |
| tmp5 = DEQUANTIZE(inptr[DCTSIZE * 3], quantptr[DCTSIZE * 3] * _0_125); |
| tmp6 = DEQUANTIZE(inptr[DCTSIZE * 5], quantptr[DCTSIZE * 5] * _0_125); |
| tmp7 = DEQUANTIZE(inptr[DCTSIZE * 7], quantptr[DCTSIZE * 7] * _0_125); |
| |
| z13 = tmp6 + tmp5; /* phase 6 */ |
| z10 = tmp6 - tmp5; |
| z11 = tmp4 + tmp7; |
| z12 = tmp4 - tmp7; |
| |
| tmp7 = z11 + z13; /* phase 5 */ |
| tmp11 = (z11 - z13) * ((FAST_FLOAT)1.414213562); /* 2*c4 */ |
| |
| z5 = (z10 + z12) * ((FAST_FLOAT)1.847759065); /* 2*c2 */ |
| tmp10 = z5 - z12 * ((FAST_FLOAT)1.082392200); /* 2*(c2-c6) */ |
| tmp12 = z5 - z10 * ((FAST_FLOAT)2.613125930); /* 2*(c2+c6) */ |
| |
| tmp6 = tmp12 - tmp7; /* phase 2 */ |
| tmp5 = tmp11 - tmp6; |
| tmp4 = tmp10 - tmp5; |
| |
| wsptr[DCTSIZE * 0] = tmp0 + tmp7; |
| wsptr[DCTSIZE * 7] = tmp0 - tmp7; |
| wsptr[DCTSIZE * 1] = tmp1 + tmp6; |
| wsptr[DCTSIZE * 6] = tmp1 - tmp6; |
| wsptr[DCTSIZE * 2] = tmp2 + tmp5; |
| wsptr[DCTSIZE * 5] = tmp2 - tmp5; |
| wsptr[DCTSIZE * 3] = tmp3 + tmp4; |
| wsptr[DCTSIZE * 4] = tmp3 - tmp4; |
| |
| inptr++; /* advance pointers to next column */ |
| quantptr++; |
| wsptr++; |
| } |
| |
| /* Pass 2: process rows from work array, store into output array. */ |
| |
| 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). |
| * And testing floats for zero is relatively expensive, so we don't bother. |
| */ |
| |
| /* Even part */ |
| |
| /* Apply signed->unsigned and prepare float->int conversion */ |
| z5 = wsptr[0] + ((FAST_FLOAT)_CENTERJSAMPLE + (FAST_FLOAT)0.5); |
| tmp10 = z5 + wsptr[4]; |
| tmp11 = z5 - wsptr[4]; |
| |
| tmp13 = wsptr[2] + wsptr[6]; |
| tmp12 = (wsptr[2] - wsptr[6]) * ((FAST_FLOAT)1.414213562) - tmp13; |
| |
| tmp0 = tmp10 + tmp13; |
| tmp3 = tmp10 - tmp13; |
| tmp1 = tmp11 + tmp12; |
| tmp2 = tmp11 - tmp12; |
| |
| /* Odd part */ |
| |
| z13 = wsptr[5] + wsptr[3]; |
| z10 = wsptr[5] - wsptr[3]; |
| z11 = wsptr[1] + wsptr[7]; |
| z12 = wsptr[1] - wsptr[7]; |
| |
| tmp7 = z11 + z13; |
| tmp11 = (z11 - z13) * ((FAST_FLOAT)1.414213562); |
| |
| z5 = (z10 + z12) * ((FAST_FLOAT)1.847759065); /* 2*c2 */ |
| tmp10 = z5 - z12 * ((FAST_FLOAT)1.082392200); /* 2*(c2-c6) */ |
| tmp12 = z5 - z10 * ((FAST_FLOAT)2.613125930); /* 2*(c2+c6) */ |
| |
| tmp6 = tmp12 - tmp7; |
| tmp5 = tmp11 - tmp6; |
| tmp4 = tmp10 - tmp5; |
| |
| /* Final output stage: float->int conversion and range-limit */ |
| |
| outptr[0] = range_limit[((int)(tmp0 + tmp7)) & RANGE_MASK]; |
| outptr[7] = range_limit[((int)(tmp0 - tmp7)) & RANGE_MASK]; |
| outptr[1] = range_limit[((int)(tmp1 + tmp6)) & RANGE_MASK]; |
| outptr[6] = range_limit[((int)(tmp1 - tmp6)) & RANGE_MASK]; |
| outptr[2] = range_limit[((int)(tmp2 + tmp5)) & RANGE_MASK]; |
| outptr[5] = range_limit[((int)(tmp2 - tmp5)) & RANGE_MASK]; |
| outptr[3] = range_limit[((int)(tmp3 + tmp4)) & RANGE_MASK]; |
| outptr[4] = range_limit[((int)(tmp3 - tmp4)) & RANGE_MASK]; |
| |
| wsptr += DCTSIZE; /* advance pointer to next row */ |
| } |
| } |
| |
| #endif /* DCT_FLOAT_SUPPORTED */ |