📄 jidctint.pas
字号:
by short-circuiting the IDCT calculation for any column in which all
the AC terms are zero. In that case each output is equal to the
DC coefficient (with scale factor as needed).
With typical images and quantization tables, half or more of the
column DCT calculations can be simplified this way. }
if ((inptr^[DCTSIZE*1]) or (inptr^[DCTSIZE*2]) or (inptr^[DCTSIZE*3]) or
(inptr^[DCTSIZE*4]) or (inptr^[DCTSIZE*5]) or (inptr^[DCTSIZE*6]) or
(inptr^[DCTSIZE*7]) = 0) then
begin
{ AC terms all zero }
dcval := DEQUANTIZE(inptr^[DCTSIZE*0], quantptr^[DCTSIZE*0]) shl PASS1_BITS;
wsptr^[DCTSIZE*0] := dcval;
wsptr^[DCTSIZE*1] := dcval;
wsptr^[DCTSIZE*2] := dcval;
wsptr^[DCTSIZE*3] := dcval;
wsptr^[DCTSIZE*4] := dcval;
wsptr^[DCTSIZE*5] := dcval;
wsptr^[DCTSIZE*6] := dcval;
wsptr^[DCTSIZE*7] := dcval;
Inc(JCOEF_PTR(inptr)); { advance pointers to next column }
Inc(ISLOW_MULT_TYPE_PTR(quantptr));
Inc(int_ptr(wsptr));
continue;
end;
{ Even part: reverse the even part of the forward DCT. }
{ The rotator is sqrt(2)*c(-6). }
z2 := DEQUANTIZE(inptr^[DCTSIZE*2], quantptr^[DCTSIZE*2]);
z3 := DEQUANTIZE(inptr^[DCTSIZE*6], quantptr^[DCTSIZE*6]);
z1 := MULTIPLY(z2 + z3, FIX_0_541196100);
tmp2 := z1 + MULTIPLY(z3, - FIX_1_847759065);
tmp3 := z1 + MULTIPLY(z2, FIX_0_765366865);
z2 := DEQUANTIZE(inptr^[DCTSIZE*0], quantptr^[DCTSIZE*0]);
z3 := DEQUANTIZE(inptr^[DCTSIZE*4], quantptr^[DCTSIZE*4]);
tmp0 := (z2 + z3) shl CONST_BITS;
tmp1 := (z2 - z3) shl CONST_BITS;
tmp10 := tmp0 + tmp3;
tmp13 := tmp0 - tmp3;
tmp11 := tmp1 + tmp2;
tmp12 := tmp1 - tmp2;
{ Odd part per figure 8; the matrix is unitary and hence its
transpose is its inverse. i0..i3 are y7,y5,y3,y1 respectively. }
tmp0 := DEQUANTIZE(inptr^[DCTSIZE*7], quantptr^[DCTSIZE*7]);
tmp1 := DEQUANTIZE(inptr^[DCTSIZE*5], quantptr^[DCTSIZE*5]);
tmp2 := DEQUANTIZE(inptr^[DCTSIZE*3], quantptr^[DCTSIZE*3]);
tmp3 := DEQUANTIZE(inptr^[DCTSIZE*1], quantptr^[DCTSIZE*1]);
z1 := tmp0 + tmp3;
z2 := tmp1 + tmp2;
z3 := tmp0 + tmp2;
z4 := tmp1 + tmp3;
z5 := MULTIPLY(z3 + z4, FIX_1_175875602); { sqrt(2) * c3 }
tmp0 := MULTIPLY(tmp0, FIX_0_298631336); { sqrt(2) * (-c1+c3+c5-c7) }
tmp1 := MULTIPLY(tmp1, FIX_2_053119869); { sqrt(2) * ( c1+c3-c5+c7) }
tmp2 := MULTIPLY(tmp2, FIX_3_072711026); { sqrt(2) * ( c1+c3+c5-c7) }
tmp3 := MULTIPLY(tmp3, FIX_1_501321110); { sqrt(2) * ( c1+c3-c5-c7) }
z1 := MULTIPLY(z1, - FIX_0_899976223); { sqrt(2) * (c7-c3) }
z2 := MULTIPLY(z2, - FIX_2_562915447); { sqrt(2) * (-c1-c3) }
z3 := MULTIPLY(z3, - FIX_1_961570560); { sqrt(2) * (-c3-c5) }
z4 := MULTIPLY(z4, - FIX_0_390180644); { sqrt(2) * (c5-c3) }
Inc(z3, z5);
Inc(z4, z5);
Inc(tmp0, z1 + z3);
Inc(tmp1, z2 + z4);
Inc(tmp2, z2 + z3);
Inc(tmp3, z1 + z4);
{ Final output stage: inputs are tmp10..tmp13, tmp0..tmp3 }
wsptr^[DCTSIZE*0] := int (DESCALE(tmp10 + tmp3, CONST_BITS-PASS1_BITS));
wsptr^[DCTSIZE*7] := int (DESCALE(tmp10 - tmp3, CONST_BITS-PASS1_BITS));
wsptr^[DCTSIZE*1] := int (DESCALE(tmp11 + tmp2, CONST_BITS-PASS1_BITS));
wsptr^[DCTSIZE*6] := int (DESCALE(tmp11 - tmp2, CONST_BITS-PASS1_BITS));
wsptr^[DCTSIZE*2] := int (DESCALE(tmp12 + tmp1, CONST_BITS-PASS1_BITS));
wsptr^[DCTSIZE*5] := int (DESCALE(tmp12 - tmp1, CONST_BITS-PASS1_BITS));
wsptr^[DCTSIZE*3] := int (DESCALE(tmp13 + tmp0, CONST_BITS-PASS1_BITS));
wsptr^[DCTSIZE*4] := int (DESCALE(tmp13 - tmp0, CONST_BITS-PASS1_BITS));
Inc(JCOEF_PTR(inptr)); { advance pointers to next column }
Inc(ISLOW_MULT_TYPE_PTR(quantptr));
Inc(int_ptr(wsptr));
end;
{ Pass 2: process rows from work array, store into output array. }
{ Note that we must descale the results by a factor of 8 == 2**3, }
{ and also undo the PASS1_BITS scaling. }
wsptr := @workspace;
for ctr := 0 to pred(DCTSIZE) do
begin
outptr := output_buf^[ctr];
Inc(JSAMPLE_PTR(outptr), output_col);
{ Rows of zeroes can be exploited in the same way as we did with columns.
However, the column calculation has created many nonzero AC terms, so
the simplification applies less often (typically 5% to 10% of the time).
On machines with very fast multiplication, it's possible that the
test takes more time than it's worth. In that case this section
may be commented out. }
{$ifndef NO_ZERO_ROW_TEST}
if ((wsptr^[1]) or (wsptr^[2]) or (wsptr^[3]) or (wsptr^[4]) or
(wsptr^[5]) or (wsptr^[6]) or (wsptr^[7]) = 0) then
begin
{ AC terms all zero }
JSAMPLE(dcval_) := range_limit^[int(DESCALE(INT32(wsptr^[0]),
PASS1_BITS+3)) and RANGE_MASK];
outptr^[0] := dcval_;
outptr^[1] := dcval_;
outptr^[2] := dcval_;
outptr^[3] := dcval_;
outptr^[4] := dcval_;
outptr^[5] := dcval_;
outptr^[6] := dcval_;
outptr^[7] := dcval_;
Inc(int_ptr(wsptr), DCTSIZE); { advance pointer to next row }
continue;
end;
{$endif}
{ Even part: reverse the even part of the forward DCT. }
{ The rotator is sqrt(2)*c(-6). }
z2 := INT32 (wsptr^[2]);
z3 := INT32 (wsptr^[6]);
z1 := MULTIPLY(z2 + z3, FIX_0_541196100);
tmp2 := z1 + MULTIPLY(z3, - FIX_1_847759065);
tmp3 := z1 + MULTIPLY(z2, FIX_0_765366865);
tmp0 := (INT32(wsptr^[0]) + INT32(wsptr^[4])) shl CONST_BITS;
tmp1 := (INT32(wsptr^[0]) - INT32(wsptr^[4])) shl CONST_BITS;
tmp10 := tmp0 + tmp3;
tmp13 := tmp0 - tmp3;
tmp11 := tmp1 + tmp2;
tmp12 := tmp1 - tmp2;
{ Odd part per figure 8; the matrix is unitary and hence its
transpose is its inverse. i0..i3 are y7,y5,y3,y1 respectively. }
tmp0 := INT32(wsptr^[7]);
tmp1 := INT32(wsptr^[5]);
tmp2 := INT32(wsptr^[3]);
tmp3 := INT32(wsptr^[1]);
z1 := tmp0 + tmp3;
z2 := tmp1 + tmp2;
z3 := tmp0 + tmp2;
z4 := tmp1 + tmp3;
z5 := MULTIPLY(z3 + z4, FIX_1_175875602); { sqrt(2) * c3 }
tmp0 := MULTIPLY(tmp0, FIX_0_298631336); { sqrt(2) * (-c1+c3+c5-c7) }
tmp1 := MULTIPLY(tmp1, FIX_2_053119869); { sqrt(2) * ( c1+c3-c5+c7) }
tmp2 := MULTIPLY(tmp2, FIX_3_072711026); { sqrt(2) * ( c1+c3+c5-c7) }
tmp3 := MULTIPLY(tmp3, FIX_1_501321110); { sqrt(2) * ( c1+c3-c5-c7) }
z1 := MULTIPLY(z1, - FIX_0_899976223); { sqrt(2) * (c7-c3) }
z2 := MULTIPLY(z2, - FIX_2_562915447); { sqrt(2) * (-c1-c3) }
z3 := MULTIPLY(z3, - FIX_1_961570560); { sqrt(2) * (-c3-c5) }
z4 := MULTIPLY(z4, - FIX_0_390180644); { sqrt(2) * (c5-c3) }
Inc(z3, z5);
Inc(z4, z5);
Inc(tmp0, z1 + z3);
Inc(tmp1, z2 + z4);
Inc(tmp2, z2 + z3);
Inc(tmp3, z1 + z4);
{ Final output stage: inputs are tmp10..tmp13, tmp0..tmp3 }
outptr^[0] := range_limit^[ int(DESCALE(tmp10 + tmp3,
CONST_BITS+PASS1_BITS+3))
and RANGE_MASK];
outptr^[7] := range_limit^[ int(DESCALE(tmp10 - tmp3,
CONST_BITS+PASS1_BITS+3))
and RANGE_MASK];
outptr^[1] := range_limit^[ int(DESCALE(tmp11 + tmp2,
CONST_BITS+PASS1_BITS+3))
and RANGE_MASK];
outptr^[6] := range_limit^[ int(DESCALE(tmp11 - tmp2,
CONST_BITS+PASS1_BITS+3))
and RANGE_MASK];
outptr^[2] := range_limit^[ int(DESCALE(tmp12 + tmp1,
CONST_BITS+PASS1_BITS+3))
and RANGE_MASK];
outptr^[5] := range_limit^[ int(DESCALE(tmp12 - tmp1,
CONST_BITS+PASS1_BITS+3))
and RANGE_MASK];
outptr^[3] := range_limit^[ int(DESCALE(tmp13 + tmp0,
CONST_BITS+PASS1_BITS+3))
and RANGE_MASK];
outptr^[4] := range_limit^[ int(DESCALE(tmp13 - tmp0,
CONST_BITS+PASS1_BITS+3))
and RANGE_MASK];
Inc(int_ptr(wsptr), DCTSIZE); { advance pointer to next row }
end;
end;
end.
⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -