| /* |
| * jidctflt.c |
| * |
| * Copyright (C) 1994-1998, Thomas G. Lane. |
| * This file is part of the Independent JPEG Group's software. |
| * |
| * The authors make NO WARRANTY or representation, either express or implied, |
| * with respect to this software, its quality, accuracy, merchantability, or |
| * fitness for a particular purpose. This software is provided "AS IS", and you, |
| * its user, assume the entire risk as to its quality and accuracy. |
| * |
| * This software is copyright (C) 1991-1998, Thomas G. Lane. |
| * All Rights Reserved except as specified below. |
| * |
| * Permission is hereby granted to use, copy, modify, and distribute this |
| * software (or portions thereof) for any purpose, without fee, subject to these |
| * conditions: |
| * (1) If any part of the source code for this software is distributed, then this |
| * README file must be included, with this copyright and no-warranty notice |
| * unaltered; and any additions, deletions, or changes to the original files |
| * must be clearly indicated in accompanying documentation. |
| * (2) If only executable code is distributed, then the accompanying |
| * documentation must state that "this software is based in part on the work of |
| * the Independent JPEG Group". |
| * (3) Permission for use of this software is granted only if the user accepts |
| * full responsibility for any undesirable consequences; the authors accept |
| * NO LIABILITY for damages of any kind. |
| * |
| * These conditions apply to any software derived from or based on the IJG code, |
| * not just to the unmodified library. If you use our work, you ought to |
| * acknowledge us. |
| * |
| * Permission is NOT granted for the use of any IJG author's name or company name |
| * in advertising or publicity relating to this software or products derived from |
| * it. This software may be referred to only as "the Independent JPEG Group's |
| * software". |
| * |
| * We specifically permit and encourage the use of this software as the basis of |
| * commercial products, provided that all warranty or liability claims are |
| * assumed by the product vendor. |
| * |
| * |
| * 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). 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. |
| */ |
| |
| #include <stdint.h> |
| #include "tinyjpeg-internal.h" |
| |
| #define FAST_FLOAT float |
| #define DCTSIZE 8 |
| #define DCTSIZE2 (DCTSIZE*DCTSIZE) |
| |
| #define DEQUANTIZE(coef,quantval) (((FAST_FLOAT) (coef)) * (quantval)) |
| |
| #if 1 && defined(__GNUC__) && (defined(__i686__) || defined(__x86_64__)) |
| |
| static inline unsigned char descale_and_clamp(int x, int shift) |
| { |
| __asm__ ( |
| "add %3,%1\n" |
| "\tsar %2,%1\n" |
| "\tsub $-128,%1\n" |
| "\tcmovl %5,%1\n" /* Use the sub to compare to 0 */ |
| "\tcmpl %4,%1\n" |
| "\tcmovg %4,%1\n" |
| : "=r"(x) |
| : "0"(x), "Ir"(shift), "ir"(1UL<<(shift-1)), "r" (0xff), "r" (0) |
| ); |
| return x; |
| } |
| |
| #else |
| static inline unsigned char descale_and_clamp(int x, int shift) |
| { |
| x += (1UL<<(shift-1)); |
| if (x<0) |
| x = (x >> shift) | ((~(0UL)) << (32-(shift))); |
| else |
| x >>= shift; |
| x += 128; |
| if (x>255) |
| return 255; |
| else if (x<0) |
| return 0; |
| else |
| return x; |
| } |
| #endif |
| |
| /* |
| * Perform dequantization and inverse DCT on one block of coefficients. |
| */ |
| |
| void |
| tinyjpeg_idct_float (struct component *compptr, uint8_t *output_buf, int stride) |
| { |
| FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7; |
| FAST_FLOAT tmp10, tmp11, tmp12, tmp13; |
| FAST_FLOAT z5, z10, z11, z12, z13; |
| int16_t *inptr; |
| FAST_FLOAT *quantptr; |
| FAST_FLOAT *wsptr; |
| uint8_t *outptr; |
| int ctr; |
| FAST_FLOAT workspace[DCTSIZE2]; /* buffers data between passes */ |
| |
| /* Pass 1: process columns from input, store into work array. */ |
| |
| inptr = compptr->DCT; |
| quantptr = compptr->Q_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]); |
| |
| 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 = (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]); |
| 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 = (z11 - z13) * ((FAST_FLOAT) 1.414213562); /* 2*c4 */ |
| |
| z5 = (z10 + z12) * ((FAST_FLOAT) 1.847759065); /* 2*c2 */ |
| tmp10 = ((FAST_FLOAT) 1.082392200) * z12 - z5; /* 2*(c2-c6) */ |
| tmp12 = ((FAST_FLOAT) -2.613125930) * z10 + z5; /* -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*4] = tmp3 + tmp4; |
| wsptr[DCTSIZE*3] = 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. */ |
| |
| wsptr = workspace; |
| outptr = output_buf; |
| for (ctr = 0; ctr < DCTSIZE; ctr++) { |
| /* 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 */ |
| |
| tmp10 = wsptr[0] + wsptr[4]; |
| tmp11 = wsptr[0] - 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 = ((FAST_FLOAT) 1.082392200) * z12 - z5; /* 2*(c2-c6) */ |
| tmp12 = ((FAST_FLOAT) -2.613125930) * z10 + z5; /* -2*(c2+c6) */ |
| |
| tmp6 = tmp12 - tmp7; |
| tmp5 = tmp11 - tmp6; |
| tmp4 = tmp10 + tmp5; |
| |
| /* Final output stage: scale down by a factor of 8 and range-limit */ |
| |
| outptr[0] = descale_and_clamp((int)(tmp0 + tmp7), 3); |
| outptr[7] = descale_and_clamp((int)(tmp0 - tmp7), 3); |
| outptr[1] = descale_and_clamp((int)(tmp1 + tmp6), 3); |
| outptr[6] = descale_and_clamp((int)(tmp1 - tmp6), 3); |
| outptr[2] = descale_and_clamp((int)(tmp2 + tmp5), 3); |
| outptr[5] = descale_and_clamp((int)(tmp2 - tmp5), 3); |
| outptr[4] = descale_and_clamp((int)(tmp3 + tmp4), 3); |
| outptr[3] = descale_and_clamp((int)(tmp3 - tmp4), 3); |
| |
| |
| wsptr += DCTSIZE; /* advance pointer to next row */ |
| outptr += stride; |
| } |
| } |