/* | |

* 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.ijg | |

* 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.ijg). 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 */ |