331 lines
9.5 KiB
Plaintext
331 lines
9.5 KiB
Plaintext
unit imjddctmgr;
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{ Original : jddctmgr.c ; Copyright (C) 1994-1996, Thomas G. Lane. }
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{ This file contains the inverse-DCT management logic.
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This code selects a particular IDCT implementation to be used,
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and it performs related housekeeping chores. No code in this file
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is executed per IDCT step, only during output pass setup.
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Note that the IDCT routines are responsible for performing coefficient
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dequantization as well as the IDCT proper. This module sets up the
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dequantization multiplier table needed by the IDCT routine. }
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interface
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{$I imjconfig.inc}
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{$N+}
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uses
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imjmorecfg,
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imjinclude,
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imjdeferr,
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imjerror,
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imjpeglib,
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imjdct, { Private declarations for DCT subsystem }
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imjidctfst,
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{$IFDEF BASM}
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imjidctasm,
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{$ELSE}
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imjidctint,
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{$ENDIF}
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imjidctflt,
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imjidctred;
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{ Initialize IDCT manager. }
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{GLOBAL}
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procedure jinit_inverse_dct (cinfo : j_decompress_ptr);
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implementation
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{ The decompressor input side (jdinput.c) saves away the appropriate
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quantization table for each component at the start of the first scan
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involving that component. (This is necessary in order to correctly
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decode files that reuse Q-table slots.)
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When we are ready to make an output pass, the saved Q-table is converted
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to a multiplier table that will actually be used by the IDCT routine.
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The multiplier table contents are IDCT-method-dependent. To support
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application changes in IDCT method between scans, we can remake the
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multiplier tables if necessary.
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In buffered-image mode, the first output pass may occur before any data
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has been seen for some components, and thus before their Q-tables have
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been saved away. To handle this case, multiplier tables are preset
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to zeroes; the result of the IDCT will be a neutral gray level. }
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{ Private subobject for this module }
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type
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my_idct_ptr = ^my_idct_controller;
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my_idct_controller = record
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pub : jpeg_inverse_dct; { public fields }
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{ This array contains the IDCT method code that each multiplier table
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is currently set up for, or -1 if it's not yet set up.
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The actual multiplier tables are pointed to by dct_table in the
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per-component comp_info structures. }
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cur_method : array[0..MAX_COMPONENTS-1] of int;
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end; {my_idct_controller;}
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{ Allocated multiplier tables: big enough for any supported variant }
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type
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multiplier_table = record
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case byte of
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0:(islow_array : array[0..DCTSIZE2-1] of ISLOW_MULT_TYPE);
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{$ifdef DCT_IFAST_SUPPORTED}
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1:(ifast_array : array[0..DCTSIZE2-1] of IFAST_MULT_TYPE);
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{$endif}
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{$ifdef DCT_FLOAT_SUPPORTED}
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2:(float_array : array[0..DCTSIZE2-1] of FLOAT_MULT_TYPE);
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{$endif}
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end;
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{ The current scaled-IDCT routines require ISLOW-style multiplier tables,
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so be sure to compile that code if either ISLOW or SCALING is requested. }
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{$ifdef DCT_ISLOW_SUPPORTED}
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{$define PROVIDE_ISLOW_TABLES}
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{$else}
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{$ifdef IDCT_SCALING_SUPPORTED}
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{$define PROVIDE_ISLOW_TABLES}
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{$endif}
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{$endif}
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{ Prepare for an output pass.
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Here we select the proper IDCT routine for each component and build
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a matching multiplier table. }
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{METHODDEF}
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procedure start_pass (cinfo : j_decompress_ptr);
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var
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idct : my_idct_ptr;
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ci, i : int;
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compptr : jpeg_component_info_ptr;
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method : J_DCT_METHOD;
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method_ptr : inverse_DCT_method_ptr;
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qtbl : JQUANT_TBL_PTR;
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{$ifdef PROVIDE_ISLOW_TABLES}
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var
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ismtbl : ISLOW_MULT_TYPE_FIELD_PTR;
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{$endif}
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{$ifdef DCT_IFAST_SUPPORTED}
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const
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CONST_BITS = 14;
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const
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aanscales : array[0..DCTSIZE2-1] of INT16 =
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({ precomputed values scaled up by 14 bits }
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16384, 22725, 21407, 19266, 16384, 12873, 8867, 4520,
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22725, 31521, 29692, 26722, 22725, 17855, 12299, 6270,
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21407, 29692, 27969, 25172, 21407, 16819, 11585, 5906,
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19266, 26722, 25172, 22654, 19266, 15137, 10426, 5315,
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16384, 22725, 21407, 19266, 16384, 12873, 8867, 4520,
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12873, 17855, 16819, 15137, 12873, 10114, 6967, 3552,
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8867, 12299, 11585, 10426, 8867, 6967, 4799, 2446,
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4520, 6270, 5906, 5315, 4520, 3552, 2446, 1247);
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var
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ifmtbl : IFAST_MULT_TYPE_FIELD_PTR;
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{SHIFT_TEMPS}
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{ Descale and correctly round an INT32 value that's scaled by N bits.
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We assume RIGHT_SHIFT rounds towards minus infinity, so adding
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the fudge factor is correct for either sign of X. }
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function DESCALE(x : INT32; n : int) : INT32;
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var
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shift_temp : INT32;
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begin
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{$ifdef RIGHT_SHIFT_IS_UNSIGNED}
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shift_temp := x + (INT32(1) shl (n-1));
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if shift_temp < 0 then
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Descale := (shift_temp shr n) or ((not INT32(0)) shl (32-n))
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else
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Descale := (shift_temp shr n);
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{$else}
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Descale := (x + (INT32(1) shl (n-1)) shr n;
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{$endif}
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end;
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{$endif}
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{$ifdef DCT_FLOAT_SUPPORTED}
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const
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aanscalefactor : array[0..DCTSIZE-1] of double =
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(1.0, 1.387039845, 1.306562965, 1.175875602,
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1.0, 0.785694958, 0.541196100, 0.275899379);
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var
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fmtbl : FLOAT_MULT_TYPE_FIELD_PTR;
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row, col : int;
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{$endif}
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begin
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idct := my_idct_ptr (cinfo^.idct);
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method := J_DCT_METHOD(0);
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method_ptr := NIL;
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compptr := jpeg_component_info_ptr(cinfo^.comp_info);
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for ci := 0 to pred(cinfo^.num_components) do
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begin
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{ Select the proper IDCT routine for this component's scaling }
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case (compptr^.DCT_scaled_size) of
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{$ifdef IDCT_SCALING_SUPPORTED}
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1:begin
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method_ptr := jpeg_idct_1x1;
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method := JDCT_ISLOW; { jidctred uses islow-style table }
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end;
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2:begin
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method_ptr := jpeg_idct_2x2;
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method := JDCT_ISLOW; { jidctred uses islow-style table }
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end;
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4:begin
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method_ptr := jpeg_idct_4x4;
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method := JDCT_ISLOW; { jidctred uses islow-style table }
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end;
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{$endif}
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DCTSIZE:
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case (cinfo^.dct_method) of
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{$ifdef DCT_ISLOW_SUPPORTED}
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JDCT_ISLOW:
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begin
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method_ptr := @jpeg_idct_islow;
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method := JDCT_ISLOW;
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end;
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{$endif}
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{$ifdef DCT_IFAST_SUPPORTED}
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JDCT_IFAST:
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begin
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method_ptr := @jpeg_idct_ifast;
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method := JDCT_IFAST;
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end;
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{$endif}
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{$ifdef DCT_FLOAT_SUPPORTED}
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JDCT_FLOAT:
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begin
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method_ptr := @jpeg_idct_float;
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method := JDCT_FLOAT;
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end;
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{$endif}
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else
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ERREXIT(j_common_ptr(cinfo), JERR_NOT_COMPILED);
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end;
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else
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ERREXIT1(j_common_ptr(cinfo), JERR_BAD_DCTSIZE, compptr^.DCT_scaled_size);
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end;
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idct^.pub.inverse_DCT[ci] := method_ptr;
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{ Create multiplier table from quant table.
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However, we can skip this if the component is uninteresting
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or if we already built the table. Also, if no quant table
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has yet been saved for the component, we leave the
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multiplier table all-zero; we'll be reading zeroes from the
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coefficient controller's buffer anyway. }
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if (not compptr^.component_needed) or (idct^.cur_method[ci] = int(method)) then
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continue;
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qtbl := compptr^.quant_table;
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if (qtbl = NIL) then { happens if no data yet for component }
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continue;
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idct^.cur_method[ci] := int(method);
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case (method) of
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{$ifdef PROVIDE_ISLOW_TABLES}
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JDCT_ISLOW:
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begin
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{ For LL&M IDCT method, multipliers are equal to raw quantization
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coefficients, but are stored as ints to ensure access efficiency. }
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ismtbl := ISLOW_MULT_TYPE_FIELD_PTR (compptr^.dct_table);
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for i := 0 to pred(DCTSIZE2) do
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begin
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ismtbl^[i] := ISLOW_MULT_TYPE (qtbl^.quantval[i]);
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end;
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end;
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{$endif}
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{$ifdef DCT_IFAST_SUPPORTED}
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JDCT_IFAST:
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begin
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{ For AA&N IDCT method, multipliers are equal to quantization
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coefficients scaled by scalefactor[row]*scalefactor[col], where
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scalefactor[0] := 1
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scalefactor[k] := cos(k*PI/16) * sqrt(2) for k=1..7
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For integer operation, the multiplier table is to be scaled by
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IFAST_SCALE_BITS. }
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ifmtbl := IFAST_MULT_TYPE_FIELD_PTR (compptr^.dct_table);
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for i := 0 to pred(DCTSIZE2) do
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begin
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ifmtbl^[i] := IFAST_MULT_TYPE(
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DESCALE( INT32 (qtbl^.quantval[i]) * INT32 (aanscales[i]),
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CONST_BITS-IFAST_SCALE_BITS) );
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end;
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end;
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{$endif}
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{$ifdef DCT_FLOAT_SUPPORTED}
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JDCT_FLOAT:
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begin
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{ For float AA&N IDCT method, multipliers are equal to quantization
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coefficients scaled by scalefactor[row]*scalefactor[col], where
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scalefactor[0] := 1
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scalefactor[k] := cos(k*PI/16) * sqrt(2) for k=1..7 }
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fmtbl := FLOAT_MULT_TYPE_FIELD_PTR(compptr^.dct_table);
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i := 0;
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for row := 0 to pred(DCTSIZE) do
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begin
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for col := 0 to pred(DCTSIZE) do
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begin
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fmtbl^[i] := {FLOAT_MULT_TYPE} (
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{double} qtbl^.quantval[i] *
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aanscalefactor[row] * aanscalefactor[col] );
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Inc(i);
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end;
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end;
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end;
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{$endif}
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else
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ERREXIT(j_common_ptr(cinfo), JERR_NOT_COMPILED);
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break;
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end;
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Inc(compptr);
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end;
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end;
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{ Initialize IDCT manager. }
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{GLOBAL}
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procedure jinit_inverse_dct (cinfo : j_decompress_ptr);
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var
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idct : my_idct_ptr;
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ci : int;
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compptr : jpeg_component_info_ptr;
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begin
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idct := my_idct_ptr(
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cinfo^.mem^.alloc_small (j_common_ptr(cinfo), JPOOL_IMAGE,
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SIZEOF(my_idct_controller)) );
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cinfo^.idct := jpeg_inverse_dct_ptr (idct);
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idct^.pub.start_pass := start_pass;
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compptr := jpeg_component_info_ptr(cinfo^.comp_info);
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for ci := 0 to pred(cinfo^.num_components) do
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begin
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{ Allocate and pre-zero a multiplier table for each component }
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compptr^.dct_table :=
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cinfo^.mem^.alloc_small (j_common_ptr(cinfo), JPOOL_IMAGE,
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SIZEOF(multiplier_table));
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MEMZERO(compptr^.dct_table, SIZEOF(multiplier_table));
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{ Mark multiplier table not yet set up for any method }
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idct^.cur_method[ci] := -1;
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Inc(compptr);
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end;
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end;
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end.
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