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Diffstat (limited to 'packages/pasjpeg/src/jfdctflt.pas')
| -rw-r--r-- | packages/pasjpeg/src/jfdctflt.pas | 176 |
1 files changed, 176 insertions, 0 deletions
diff --git a/packages/pasjpeg/src/jfdctflt.pas b/packages/pasjpeg/src/jfdctflt.pas new file mode 100644 index 0000000000..9dddb4fb25 --- /dev/null +++ b/packages/pasjpeg/src/jfdctflt.pas @@ -0,0 +1,176 @@ +Unit JFDctFlt; + +{$N+} +{ This file contains a floating-point implementation of the + forward DCT (Discrete Cosine Transform). + + This implementation should be more accurate than either of the integer + DCT implementations. However, it may not give the same results on all + machines because of differences in roundoff behavior. Speed will depend + on the hardware's floating point capacity. + + A 2-D DCT can be done by 1-D DCT on each row followed by 1-D DCT + on each column. Direct algorithms are also available, but they are + much more complex and seem not to be any faster when reduced to code. + + This implementation is based on Arai, Agui, and Nakajima's algorithm for + scaled DCT. Their original paper (Trans. IEICE E-71(11):1095) is in + Japanese, but the algorithm is described in the Pennebaker & Mitchell + JPEG textbook (see REFERENCES section in file README). The following code + is based directly on figure 4-8 in P&M. + While an 8-point DCT cannot be done in less than 11 multiplies, it is + possible to arrange the computation so that many of the multiplies are + simple scalings of the final outputs. These multiplies can then be + folded into the multiplications or divisions by the JPEG quantization + table entries. The AA&N method leaves only 5 multiplies and 29 adds + to be done in the DCT itself. + The primary disadvantage of this method is that with a fixed-point + implementation, accuracy is lost due to imprecise representation of the + scaled quantization values. However, that problem does not arise if + we use floating point arithmetic. } + +{ Original : jfdctflt.c ; Copyright (C) 1994-1996, Thomas G. Lane. } + +interface + +{$I jconfig.inc} + +uses + jmorecfg, + jinclude, + jpeglib, + jdct; { Private declarations for DCT subsystem } + + +{ Perform the forward DCT on one block of samples.} + +{GLOBAL} +procedure jpeg_fdct_float (var data : array of FAST_FLOAT); + +implementation + +{ This module is specialized to the case DCTSIZE = 8. } + +{$ifndef DCTSIZE_IS_8} + Sorry, this code only copes with 8x8 DCTs. { deliberate syntax err } +{$endif} + + +{ Perform the forward DCT on one block of samples.} + +{GLOBAL} +procedure jpeg_fdct_float (var data : array of FAST_FLOAT); +type + PWorkspace = ^TWorkspace; + TWorkspace = array [0..DCTSIZE2-1] of FAST_FLOAT; +var + 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 : PWorkspace; + ctr : int; +begin + { Pass 1: process rows. } + + dataptr := PWorkspace(@data); + for ctr := DCTSIZE-1 downto 0 do + begin + 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; + + Inc(FAST_FLOAT_PTR(dataptr), DCTSIZE); { advance pointer to next row } + end; + + { Pass 2: process columns. } + + dataptr := PWorkspace(@data); + for ctr := DCTSIZE-1 downto 0 do + begin + 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; + + Inc(FAST_FLOAT_PTR(dataptr)); { advance pointer to next column } + end; +end; + +end. |