1 /* 2 * jfdctflt.c 3 * 4 * Copyright (C) 1994-1996, Thomas G. Lane. 5 * Modified 2003-2009 by Guido Vollbeding. 6 * This file is part of the Independent JPEG Group's software. 7 * For conditions of distribution and use, see the accompanying README file. 8 * 9 * This file contains a floating-point implementation of the 10 * forward DCT (Discrete Cosine Transform). 11 * 12 * This implementation should be more accurate than either of the integer 13 * DCT implementations. However, it may not give the same results on all 14 * machines because of differences in roundoff behavior. Speed will depend 15 * on the hardware's floating point capacity. 16 * 17 * A 2-D DCT can be done by 1-D DCT on each row followed by 1-D DCT 18 * on each column. Direct algorithms are also available, but they are 19 * much more complex and seem not to be any faster when reduced to code. 20 * 21 * This implementation is based on Arai, Agui, and Nakajima's algorithm for 22 * scaled DCT. Their original paper (Trans. IEICE E-71(11):1095) is in 23 * Japanese, but the algorithm is described in the Pennebaker & Mitchell 24 * JPEG textbook (see REFERENCES section in file README). The following code 25 * is based directly on figure 4-8 in P&M. 26 * While an 8-point DCT cannot be done in less than 11 multiplies, it is 27 * possible to arrange the computation so that many of the multiplies are 28 * simple scalings of the final outputs. These multiplies can then be 29 * folded into the multiplications or divisions by the JPEG quantization 30 * table entries. The AA&N method leaves only 5 multiplies and 29 adds 31 * to be done in the DCT itself. 32 * The primary disadvantage of this method is that with a fixed-point 33 * implementation, accuracy is lost due to imprecise representation of the 34 * scaled quantization values. However, that problem does not arise if 35 * we use floating point arithmetic. 36 */ 37 38 #define JPEG_INTERNALS 39 #include "jinclude.h" 40 #include "jpeglib.h" 41 #include "jdct.h" /* Private declarations for DCT subsystem */ 42 43 #ifdef DCT_FLOAT_SUPPORTED 44 45 46 /* 47 * This module is specialized to the case DCTSIZE = 8. 48 */ 49 50 #if DCTSIZE != 8 51 Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */ 52 #endif 53 54 55 /* 56 * Perform the forward DCT on one block of samples. 57 */ 58 59 GLOBAL(void) 60 jpeg_fdct_float (FAST_FLOAT * data, JSAMPARRAY sample_data, JDIMENSION start_col) 61 { 62 FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7; 63 FAST_FLOAT tmp10, tmp11, tmp12, tmp13; 64 FAST_FLOAT z1, z2, z3, z4, z5, z11, z13; 65 FAST_FLOAT *dataptr; 66 JSAMPROW elemptr; 67 int ctr; 68 69 /* Pass 1: process rows. */ 70 71 dataptr = data; 72 for (ctr = 0; ctr < DCTSIZE; ctr++) { 73 elemptr = sample_data[ctr] + start_col; 74 75 /* Load data into workspace */ 76 tmp0 = (FAST_FLOAT) (GETJSAMPLE(elemptr[0]) + GETJSAMPLE(elemptr[7])); 77 tmp7 = (FAST_FLOAT) (GETJSAMPLE(elemptr[0]) - GETJSAMPLE(elemptr[7])); 78 tmp1 = (FAST_FLOAT) (GETJSAMPLE(elemptr[1]) + GETJSAMPLE(elemptr[6])); 79 tmp6 = (FAST_FLOAT) (GETJSAMPLE(elemptr[1]) - GETJSAMPLE(elemptr[6])); 80 tmp2 = (FAST_FLOAT) (GETJSAMPLE(elemptr[2]) + GETJSAMPLE(elemptr[5])); 81 tmp5 = (FAST_FLOAT) (GETJSAMPLE(elemptr[2]) - GETJSAMPLE(elemptr[5])); 82 tmp3 = (FAST_FLOAT) (GETJSAMPLE(elemptr[3]) + GETJSAMPLE(elemptr[4])); 83 tmp4 = (FAST_FLOAT) (GETJSAMPLE(elemptr[3]) - GETJSAMPLE(elemptr[4])); 84 85 /* Even part */ 86 87 tmp10 = tmp0 + tmp3; /* phase 2 */ 88 tmp13 = tmp0 - tmp3; 89 tmp11 = tmp1 + tmp2; 90 tmp12 = tmp1 - tmp2; 91 92 /* Apply unsigned->signed conversion */ 93 dataptr[0] = tmp10 + tmp11 - 8 * CENTERJSAMPLE; /* phase 3 */ 94 dataptr[4] = tmp10 - tmp11; 95 96 z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */ 97 dataptr[2] = tmp13 + z1; /* phase 5 */ 98 dataptr[6] = tmp13 - z1; 99 100 /* Odd part */ 101 102 tmp10 = tmp4 + tmp5; /* phase 2 */ 103 tmp11 = tmp5 + tmp6; 104 tmp12 = tmp6 + tmp7; 105 106 /* The rotator is modified from fig 4-8 to avoid extra negations. */ 107 z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */ 108 z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */ 109 z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */ 110 z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */ 111 112 z11 = tmp7 + z3; /* phase 5 */ 113 z13 = tmp7 - z3; 114 115 dataptr[5] = z13 + z2; /* phase 6 */ 116 dataptr[3] = z13 - z2; 117 dataptr[1] = z11 + z4; 118 dataptr[7] = z11 - z4; 119 120 dataptr += DCTSIZE; /* advance pointer to next row */ 121 } 122 123 /* Pass 2: process columns. */ 124 125 dataptr = data; 126 for (ctr = DCTSIZE-1; ctr >= 0; ctr--) { 127 tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7]; 128 tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7]; 129 tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6]; 130 tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6]; 131 tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5]; 132 tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5]; 133 tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4]; 134 tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4]; 135 136 /* Even part */ 137 138 tmp10 = tmp0 + tmp3; /* phase 2 */ 139 tmp13 = tmp0 - tmp3; 140 tmp11 = tmp1 + tmp2; 141 tmp12 = tmp1 - tmp2; 142 143 dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */ 144 dataptr[DCTSIZE*4] = tmp10 - tmp11; 145 146 z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */ 147 dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */ 148 dataptr[DCTSIZE*6] = tmp13 - z1; 149 150 /* Odd part */ 151 152 tmp10 = tmp4 + tmp5; /* phase 2 */ 153 tmp11 = tmp5 + tmp6; 154 tmp12 = tmp6 + tmp7; 155 156 /* The rotator is modified from fig 4-8 to avoid extra negations. */ 157 z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */ 158 z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */ 159 z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */ 160 z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */ 161 162 z11 = tmp7 + z3; /* phase 5 */ 163 z13 = tmp7 - z3; 164 165 dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */ 166 dataptr[DCTSIZE*3] = z13 - z2; 167 dataptr[DCTSIZE*1] = z11 + z4; 168 dataptr[DCTSIZE*7] = z11 - z4; 169 170 dataptr++; /* advance pointer to next column */ 171 } 172 } 173 174 #endif /* DCT_FLOAT_SUPPORTED */ 175
