Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 1 | /* |
| 2 | * jfdctfst.c |
| 3 | * |
DRC | 1e32fe3 | 2015-10-14 17:32:39 -0500 | [diff] [blame] | 4 | * This file was part of the Independent JPEG Group's software: |
Thomas G. Lane | 489583f | 1996-02-07 00:00:00 +0000 | [diff] [blame] | 5 | * Copyright (C) 1994-1996, Thomas G. Lane. |
DRC | 1e32fe3 | 2015-10-14 17:32:39 -0500 | [diff] [blame] | 6 | * libjpeg-turbo Modifications: |
| 7 | * Copyright (C) 2015, D. R. Commander |
DRC | 7e3acc0 | 2015-10-10 10:25:46 -0500 | [diff] [blame] | 8 | * For conditions of distribution and use, see the accompanying README.ijg |
| 9 | * file. |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 10 | * |
| 11 | * This file contains a fast, not so accurate integer implementation of the |
| 12 | * forward DCT (Discrete Cosine Transform). |
| 13 | * |
| 14 | * A 2-D DCT can be done by 1-D DCT on each row followed by 1-D DCT |
| 15 | * on each column. Direct algorithms are also available, but they are |
| 16 | * much more complex and seem not to be any faster when reduced to code. |
| 17 | * |
| 18 | * This implementation is based on Arai, Agui, and Nakajima's algorithm for |
| 19 | * scaled DCT. Their original paper (Trans. IEICE E-71(11):1095) is in |
| 20 | * Japanese, but the algorithm is described in the Pennebaker & Mitchell |
DRC | 7e3acc0 | 2015-10-10 10:25:46 -0500 | [diff] [blame] | 21 | * JPEG textbook (see REFERENCES section in file README.ijg). The following |
| 22 | * code is based directly on figure 4-8 in P&M. |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 23 | * While an 8-point DCT cannot be done in less than 11 multiplies, it is |
| 24 | * possible to arrange the computation so that many of the multiplies are |
| 25 | * simple scalings of the final outputs. These multiplies can then be |
| 26 | * folded into the multiplications or divisions by the JPEG quantization |
| 27 | * table entries. The AA&N method leaves only 5 multiplies and 29 adds |
| 28 | * to be done in the DCT itself. |
| 29 | * The primary disadvantage of this method is that with fixed-point math, |
| 30 | * accuracy is lost due to imprecise representation of the scaled |
| 31 | * quantization values. The smaller the quantization table entry, the less |
| 32 | * precise the scaled value, so this implementation does worse with high- |
| 33 | * quality-setting files than with low-quality ones. |
| 34 | */ |
| 35 | |
| 36 | #define JPEG_INTERNALS |
| 37 | #include "jinclude.h" |
| 38 | #include "jpeglib.h" |
DRC | e5eaf37 | 2014-05-09 18:00:32 +0000 | [diff] [blame] | 39 | #include "jdct.h" /* Private declarations for DCT subsystem */ |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 40 | |
| 41 | #ifdef DCT_IFAST_SUPPORTED |
| 42 | |
| 43 | |
| 44 | /* |
| 45 | * This module is specialized to the case DCTSIZE = 8. |
| 46 | */ |
| 47 | |
| 48 | #if DCTSIZE != 8 |
| 49 | Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */ |
| 50 | #endif |
| 51 | |
| 52 | |
| 53 | /* Scaling decisions are generally the same as in the LL&M algorithm; |
| 54 | * see jfdctint.c for more details. However, we choose to descale |
| 55 | * (right shift) multiplication products as soon as they are formed, |
| 56 | * rather than carrying additional fractional bits into subsequent additions. |
| 57 | * This compromises accuracy slightly, but it lets us save a few shifts. |
| 58 | * More importantly, 16-bit arithmetic is then adequate (for 8-bit samples) |
| 59 | * everywhere except in the multiplications proper; this saves a good deal |
| 60 | * of work on 16-bit-int machines. |
| 61 | * |
| 62 | * Again to save a few shifts, the intermediate results between pass 1 and |
| 63 | * pass 2 are not upscaled, but are represented only to integral precision. |
| 64 | * |
| 65 | * A final compromise is to represent the multiplicative constants to only |
| 66 | * 8 fractional bits, rather than 13. This saves some shifting work on some |
| 67 | * machines, and may also reduce the cost of multiplication (since there |
| 68 | * are fewer one-bits in the constants). |
| 69 | */ |
| 70 | |
| 71 | #define CONST_BITS 8 |
| 72 | |
| 73 | |
| 74 | /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus |
| 75 | * causing a lot of useless floating-point operations at run time. |
| 76 | * To get around this we use the following pre-calculated constants. |
| 77 | * If you change CONST_BITS you may want to add appropriate values. |
| 78 | * (With a reasonable C compiler, you can just rely on the FIX() macro...) |
| 79 | */ |
| 80 | |
| 81 | #if CONST_BITS == 8 |
DRC | 1e32fe3 | 2015-10-14 17:32:39 -0500 | [diff] [blame] | 82 | #define FIX_0_382683433 ((JLONG) 98) /* FIX(0.382683433) */ |
| 83 | #define FIX_0_541196100 ((JLONG) 139) /* FIX(0.541196100) */ |
| 84 | #define FIX_0_707106781 ((JLONG) 181) /* FIX(0.707106781) */ |
| 85 | #define FIX_1_306562965 ((JLONG) 334) /* FIX(1.306562965) */ |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 86 | #else |
| 87 | #define FIX_0_382683433 FIX(0.382683433) |
| 88 | #define FIX_0_541196100 FIX(0.541196100) |
| 89 | #define FIX_0_707106781 FIX(0.707106781) |
| 90 | #define FIX_1_306562965 FIX(1.306562965) |
| 91 | #endif |
| 92 | |
| 93 | |
| 94 | /* We can gain a little more speed, with a further compromise in accuracy, |
| 95 | * by omitting the addition in a descaling shift. This yields an incorrectly |
| 96 | * rounded result half the time... |
| 97 | */ |
| 98 | |
| 99 | #ifndef USE_ACCURATE_ROUNDING |
| 100 | #undef DESCALE |
| 101 | #define DESCALE(x,n) RIGHT_SHIFT(x, n) |
| 102 | #endif |
| 103 | |
| 104 | |
DRC | 1e32fe3 | 2015-10-14 17:32:39 -0500 | [diff] [blame] | 105 | /* Multiply a DCTELEM variable by an JLONG constant, and immediately |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 106 | * descale to yield a DCTELEM result. |
| 107 | */ |
| 108 | |
| 109 | #define MULTIPLY(var,const) ((DCTELEM) DESCALE((var) * (const), CONST_BITS)) |
| 110 | |
| 111 | |
| 112 | /* |
| 113 | * Perform the forward DCT on one block of samples. |
| 114 | */ |
| 115 | |
Thomas G. Lane | 489583f | 1996-02-07 00:00:00 +0000 | [diff] [blame] | 116 | GLOBAL(void) |
DRC | bd49803 | 2016-02-19 08:53:33 -0600 | [diff] [blame^] | 117 | jpeg_fdct_ifast (DCTELEM *data) |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 118 | { |
| 119 | DCTELEM tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7; |
| 120 | DCTELEM tmp10, tmp11, tmp12, tmp13; |
| 121 | DCTELEM z1, z2, z3, z4, z5, z11, z13; |
| 122 | DCTELEM *dataptr; |
| 123 | int ctr; |
| 124 | SHIFT_TEMPS |
| 125 | |
| 126 | /* Pass 1: process rows. */ |
| 127 | |
| 128 | dataptr = data; |
| 129 | for (ctr = DCTSIZE-1; ctr >= 0; ctr--) { |
| 130 | tmp0 = dataptr[0] + dataptr[7]; |
| 131 | tmp7 = dataptr[0] - dataptr[7]; |
| 132 | tmp1 = dataptr[1] + dataptr[6]; |
| 133 | tmp6 = dataptr[1] - dataptr[6]; |
| 134 | tmp2 = dataptr[2] + dataptr[5]; |
| 135 | tmp5 = dataptr[2] - dataptr[5]; |
| 136 | tmp3 = dataptr[3] + dataptr[4]; |
| 137 | tmp4 = dataptr[3] - dataptr[4]; |
DRC | e5eaf37 | 2014-05-09 18:00:32 +0000 | [diff] [blame] | 138 | |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 139 | /* Even part */ |
DRC | e5eaf37 | 2014-05-09 18:00:32 +0000 | [diff] [blame] | 140 | |
| 141 | tmp10 = tmp0 + tmp3; /* phase 2 */ |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 142 | tmp13 = tmp0 - tmp3; |
| 143 | tmp11 = tmp1 + tmp2; |
| 144 | tmp12 = tmp1 - tmp2; |
DRC | e5eaf37 | 2014-05-09 18:00:32 +0000 | [diff] [blame] | 145 | |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 146 | dataptr[0] = tmp10 + tmp11; /* phase 3 */ |
| 147 | dataptr[4] = tmp10 - tmp11; |
DRC | e5eaf37 | 2014-05-09 18:00:32 +0000 | [diff] [blame] | 148 | |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 149 | z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781); /* c4 */ |
DRC | e5eaf37 | 2014-05-09 18:00:32 +0000 | [diff] [blame] | 150 | dataptr[2] = tmp13 + z1; /* phase 5 */ |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 151 | dataptr[6] = tmp13 - z1; |
DRC | e5eaf37 | 2014-05-09 18:00:32 +0000 | [diff] [blame] | 152 | |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 153 | /* Odd part */ |
| 154 | |
DRC | e5eaf37 | 2014-05-09 18:00:32 +0000 | [diff] [blame] | 155 | tmp10 = tmp4 + tmp5; /* phase 2 */ |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 156 | tmp11 = tmp5 + tmp6; |
| 157 | tmp12 = tmp6 + tmp7; |
| 158 | |
| 159 | /* The rotator is modified from fig 4-8 to avoid extra negations. */ |
| 160 | z5 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */ |
| 161 | z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5; /* c2-c6 */ |
| 162 | z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5; /* c2+c6 */ |
| 163 | z3 = MULTIPLY(tmp11, FIX_0_707106781); /* c4 */ |
| 164 | |
DRC | e5eaf37 | 2014-05-09 18:00:32 +0000 | [diff] [blame] | 165 | z11 = tmp7 + z3; /* phase 5 */ |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 166 | z13 = tmp7 - z3; |
| 167 | |
DRC | e5eaf37 | 2014-05-09 18:00:32 +0000 | [diff] [blame] | 168 | dataptr[5] = z13 + z2; /* phase 6 */ |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 169 | dataptr[3] = z13 - z2; |
| 170 | dataptr[1] = z11 + z4; |
| 171 | dataptr[7] = z11 - z4; |
| 172 | |
DRC | e5eaf37 | 2014-05-09 18:00:32 +0000 | [diff] [blame] | 173 | dataptr += DCTSIZE; /* advance pointer to next row */ |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 174 | } |
| 175 | |
| 176 | /* Pass 2: process columns. */ |
| 177 | |
| 178 | dataptr = data; |
| 179 | for (ctr = DCTSIZE-1; ctr >= 0; ctr--) { |
| 180 | tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7]; |
| 181 | tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7]; |
| 182 | tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6]; |
| 183 | tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6]; |
| 184 | tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5]; |
| 185 | tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5]; |
| 186 | tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4]; |
| 187 | tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4]; |
DRC | e5eaf37 | 2014-05-09 18:00:32 +0000 | [diff] [blame] | 188 | |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 189 | /* Even part */ |
DRC | e5eaf37 | 2014-05-09 18:00:32 +0000 | [diff] [blame] | 190 | |
| 191 | tmp10 = tmp0 + tmp3; /* phase 2 */ |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 192 | tmp13 = tmp0 - tmp3; |
| 193 | tmp11 = tmp1 + tmp2; |
| 194 | tmp12 = tmp1 - tmp2; |
DRC | e5eaf37 | 2014-05-09 18:00:32 +0000 | [diff] [blame] | 195 | |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 196 | dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */ |
| 197 | dataptr[DCTSIZE*4] = tmp10 - tmp11; |
DRC | e5eaf37 | 2014-05-09 18:00:32 +0000 | [diff] [blame] | 198 | |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 199 | z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781); /* c4 */ |
| 200 | dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */ |
| 201 | dataptr[DCTSIZE*6] = tmp13 - z1; |
DRC | e5eaf37 | 2014-05-09 18:00:32 +0000 | [diff] [blame] | 202 | |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 203 | /* Odd part */ |
| 204 | |
DRC | e5eaf37 | 2014-05-09 18:00:32 +0000 | [diff] [blame] | 205 | tmp10 = tmp4 + tmp5; /* phase 2 */ |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 206 | tmp11 = tmp5 + tmp6; |
| 207 | tmp12 = tmp6 + tmp7; |
| 208 | |
| 209 | /* The rotator is modified from fig 4-8 to avoid extra negations. */ |
| 210 | z5 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */ |
| 211 | z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5; /* c2-c6 */ |
| 212 | z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5; /* c2+c6 */ |
| 213 | z3 = MULTIPLY(tmp11, FIX_0_707106781); /* c4 */ |
| 214 | |
DRC | e5eaf37 | 2014-05-09 18:00:32 +0000 | [diff] [blame] | 215 | z11 = tmp7 + z3; /* phase 5 */ |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 216 | z13 = tmp7 - z3; |
| 217 | |
| 218 | dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */ |
| 219 | dataptr[DCTSIZE*3] = z13 - z2; |
| 220 | dataptr[DCTSIZE*1] = z11 + z4; |
| 221 | dataptr[DCTSIZE*7] = z11 - z4; |
| 222 | |
DRC | e5eaf37 | 2014-05-09 18:00:32 +0000 | [diff] [blame] | 223 | dataptr++; /* advance pointer to next column */ |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 224 | } |
| 225 | } |
| 226 | |
| 227 | #endif /* DCT_IFAST_SUPPORTED */ |