www.pudn.com > imgport.rar > jfdctflt.c, change:2008-11-05,size:5654b


/* 
 * jfdctflt.c 
 * 
 * Copyright (C) 1994-1996, Thomas G. Lane. 
 * This file is part of the Independent JPEG Group's software. 
 * For conditions of distribution and use, see the accompanying README file. 
 * 
 * This file contains a floating-point implementation of the 
 * forward DCT (Discrete Cosine Transform). 
 * 
 * This implementation should be more accurate than either of the integer 
 * DCT 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 DCT can be done by 1-D DCT on each row followed by 1-D DCT 
 * on each column.  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. 
 */ 
 
#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 
 
 
/* 
 * Perform the forward DCT on one block of samples. 
 */ 
 
GLOBAL(void) 
jpeg_fdct_float (FAST_FLOAT * data) 
{ 
  FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7; 
  FAST_FLOAT tmp10, tmp11, tmp12, tmp13; 
  FAST_FLOAT z1, z2, z3, z4, z5, z11, z13; 
  FAST_FLOAT *dataptr; 
  int ctr; 
 
  /* Pass 1: process rows. */ 
 
  dataptr = data; 
  for (ctr = DCTSIZE-1; ctr >= 0; ctr--) { 
    tmp0 = dataptr[0] + dataptr[7]; 
    tmp7 = dataptr[0] - dataptr[7]; 
    tmp1 = dataptr[1] + dataptr[6]; 
    tmp6 = dataptr[1] - dataptr[6]; 
    tmp2 = dataptr[2] + dataptr[5]; 
    tmp5 = dataptr[2] - dataptr[5]; 
    tmp3 = dataptr[3] + dataptr[4]; 
    tmp4 = dataptr[3] - dataptr[4]; 
     
    /* Even part */ 
     
    tmp10 = tmp0 + tmp3;	/* phase 2 */ 
    tmp13 = tmp0 - tmp3; 
    tmp11 = tmp1 + tmp2; 
    tmp12 = tmp1 - tmp2; 
     
    dataptr[0] = tmp10 + tmp11; /* phase 3 */ 
    dataptr[4] = tmp10 - tmp11; 
     
    z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */ 
    dataptr[2] = tmp13 + z1;	/* phase 5 */ 
    dataptr[6] = tmp13 - z1; 
     
    /* Odd part */ 
 
    tmp10 = tmp4 + tmp5;	/* phase 2 */ 
    tmp11 = tmp5 + tmp6; 
    tmp12 = tmp6 + tmp7; 
 
    /* The rotator is modified from fig 4-8 to avoid extra negations. */ 
    z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */ 
    z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */ 
    z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */ 
    z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */ 
 
    z11 = tmp7 + z3;		/* phase 5 */ 
    z13 = tmp7 - z3; 
 
    dataptr[5] = z13 + z2;	/* phase 6 */ 
    dataptr[3] = z13 - z2; 
    dataptr[1] = z11 + z4; 
    dataptr[7] = z11 - z4; 
 
    dataptr += DCTSIZE;		/* advance pointer to next row */ 
  } 
 
  /* Pass 2: process columns. */ 
 
  dataptr = data; 
  for (ctr = DCTSIZE-1; ctr >= 0; ctr--) { 
    tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7]; 
    tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7]; 
    tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6]; 
    tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6]; 
    tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5]; 
    tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5]; 
    tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4]; 
    tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4]; 
     
    /* Even part */ 
     
    tmp10 = tmp0 + tmp3;	/* phase 2 */ 
    tmp13 = tmp0 - tmp3; 
    tmp11 = tmp1 + tmp2; 
    tmp12 = tmp1 - tmp2; 
     
    dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */ 
    dataptr[DCTSIZE*4] = tmp10 - tmp11; 
     
    z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */ 
    dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */ 
    dataptr[DCTSIZE*6] = tmp13 - z1; 
     
    /* Odd part */ 
 
    tmp10 = tmp4 + tmp5;	/* phase 2 */ 
    tmp11 = tmp5 + tmp6; 
    tmp12 = tmp6 + tmp7; 
 
    /* The rotator is modified from fig 4-8 to avoid extra negations. */ 
    z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */ 
    z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */ 
    z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */ 
    z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */ 
 
    z11 = tmp7 + z3;		/* phase 5 */ 
    z13 = tmp7 - z3; 
 
    dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */ 
    dataptr[DCTSIZE*3] = z13 - z2; 
    dataptr[DCTSIZE*1] = z11 + z4; 
    dataptr[DCTSIZE*7] = z11 - z4; 
 
    dataptr++;			/* advance pointer to next column */ 
  } 
} 
 
#endif /* DCT_FLOAT_SUPPORTED */