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/media/libjpeg/jfdctflt.c

http://github.com/zpao/v8monkey
C | 168 lines | 86 code | 33 blank | 49 comment | 3 complexity | 6c0522409d7e8d81a2b2f0892c34d8ad MD5 | raw file
  1/*
  2 * jfdctflt.c
  3 *
  4 * Copyright (C) 1994-1996, Thomas G. Lane.
  5 * This file is part of the Independent JPEG Group's software.
  6 * For conditions of distribution and use, see the accompanying README file.
  7 *
  8 * This file contains a floating-point implementation of the
  9 * forward DCT (Discrete Cosine Transform).
 10 *
 11 * This implementation should be more accurate than either of the integer
 12 * DCT implementations.  However, it may not give the same results on all
 13 * machines because of differences in roundoff behavior.  Speed will depend
 14 * on the hardware's floating point capacity.
 15 *
 16 * A 2-D DCT can be done by 1-D DCT on each row followed by 1-D DCT
 17 * on each column.  Direct algorithms are also available, but they are
 18 * much more complex and seem not to be any faster when reduced to code.
 19 *
 20 * This implementation is based on Arai, Agui, and Nakajima's algorithm for
 21 * scaled DCT.  Their original paper (Trans. IEICE E-71(11):1095) is in
 22 * Japanese, but the algorithm is described in the Pennebaker & Mitchell
 23 * JPEG textbook (see REFERENCES section in file README).  The following code
 24 * is based directly on figure 4-8 in P&M.
 25 * While an 8-point DCT cannot be done in less than 11 multiplies, it is
 26 * possible to arrange the computation so that many of the multiplies are
 27 * simple scalings of the final outputs.  These multiplies can then be
 28 * folded into the multiplications or divisions by the JPEG quantization
 29 * table entries.  The AA&N method leaves only 5 multiplies and 29 adds
 30 * to be done in the DCT itself.
 31 * The primary disadvantage of this method is that with a fixed-point
 32 * implementation, accuracy is lost due to imprecise representation of the
 33 * scaled quantization values.  However, that problem does not arise if
 34 * we use floating point arithmetic.
 35 */
 36
 37#define JPEG_INTERNALS
 38#include "jinclude.h"
 39#include "jpeglib.h"
 40#include "jdct.h"		/* Private declarations for DCT subsystem */
 41
 42#ifdef DCT_FLOAT_SUPPORTED
 43
 44
 45/*
 46 * This module is specialized to the case DCTSIZE = 8.
 47 */
 48
 49#if DCTSIZE != 8
 50  Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
 51#endif
 52
 53
 54/*
 55 * Perform the forward DCT on one block of samples.
 56 */
 57
 58GLOBAL(void)
 59jpeg_fdct_float (FAST_FLOAT * data)
 60{
 61  FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
 62  FAST_FLOAT tmp10, tmp11, tmp12, tmp13;
 63  FAST_FLOAT z1, z2, z3, z4, z5, z11, z13;
 64  FAST_FLOAT *dataptr;
 65  int ctr;
 66
 67  /* Pass 1: process rows. */
 68
 69  dataptr = data;
 70  for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
 71    tmp0 = dataptr[0] + dataptr[7];
 72    tmp7 = dataptr[0] - dataptr[7];
 73    tmp1 = dataptr[1] + dataptr[6];
 74    tmp6 = dataptr[1] - dataptr[6];
 75    tmp2 = dataptr[2] + dataptr[5];
 76    tmp5 = dataptr[2] - dataptr[5];
 77    tmp3 = dataptr[3] + dataptr[4];
 78    tmp4 = dataptr[3] - dataptr[4];
 79    
 80    /* Even part */
 81    
 82    tmp10 = tmp0 + tmp3;	/* phase 2 */
 83    tmp13 = tmp0 - tmp3;
 84    tmp11 = tmp1 + tmp2;
 85    tmp12 = tmp1 - tmp2;
 86    
 87    dataptr[0] = tmp10 + tmp11; /* phase 3 */
 88    dataptr[4] = tmp10 - tmp11;
 89    
 90    z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */
 91    dataptr[2] = tmp13 + z1;	/* phase 5 */
 92    dataptr[6] = tmp13 - z1;
 93    
 94    /* Odd part */
 95
 96    tmp10 = tmp4 + tmp5;	/* phase 2 */
 97    tmp11 = tmp5 + tmp6;
 98    tmp12 = tmp6 + tmp7;
 99
100    /* The rotator is modified from fig 4-8 to avoid extra negations. */
101    z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */
102    z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */
103    z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */
104    z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */
105
106    z11 = tmp7 + z3;		/* phase 5 */
107    z13 = tmp7 - z3;
108
109    dataptr[5] = z13 + z2;	/* phase 6 */
110    dataptr[3] = z13 - z2;
111    dataptr[1] = z11 + z4;
112    dataptr[7] = z11 - z4;
113
114    dataptr += DCTSIZE;		/* advance pointer to next row */
115  }
116
117  /* Pass 2: process columns. */
118
119  dataptr = data;
120  for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
121    tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7];
122    tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7];
123    tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6];
124    tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6];
125    tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5];
126    tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5];
127    tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4];
128    tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4];
129    
130    /* Even part */
131    
132    tmp10 = tmp0 + tmp3;	/* phase 2 */
133    tmp13 = tmp0 - tmp3;
134    tmp11 = tmp1 + tmp2;
135    tmp12 = tmp1 - tmp2;
136    
137    dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */
138    dataptr[DCTSIZE*4] = tmp10 - tmp11;
139    
140    z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */
141    dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */
142    dataptr[DCTSIZE*6] = tmp13 - z1;
143    
144    /* Odd part */
145
146    tmp10 = tmp4 + tmp5;	/* phase 2 */
147    tmp11 = tmp5 + tmp6;
148    tmp12 = tmp6 + tmp7;
149
150    /* The rotator is modified from fig 4-8 to avoid extra negations. */
151    z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */
152    z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */
153    z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */
154    z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */
155
156    z11 = tmp7 + z3;		/* phase 5 */
157    z13 = tmp7 - z3;
158
159    dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */
160    dataptr[DCTSIZE*3] = z13 - z2;
161    dataptr[DCTSIZE*1] = z11 + z4;
162    dataptr[DCTSIZE*7] = z11 - z4;
163
164    dataptr++;			/* advance pointer to next column */
165  }
166}
167
168#endif /* DCT_FLOAT_SUPPORTED */