176 lines
7 KiB
C
176 lines
7 KiB
C
/*
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* jdct.h
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*
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* Copyright (C) 1994, Thomas G. Lane.
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* This file is part of the Independent JPEG Group's software.
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* For conditions of distribution and use, see the accompanying README file.
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*
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* This include file contains common declarations for the forward and
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* inverse DCT modules. These declarations are private to the DCT managers
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* (jcdctmgr.c, jddctmgr.c) and the individual DCT algorithms.
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* The individual DCT algorithms are kept in separate files to ease
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* machine-dependent tuning (e.g., assembly coding).
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*/
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/*
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* A forward DCT routine is given a pointer to a work area of type DCTELEM[];
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* the DCT is to be performed in-place in that buffer. Type DCTELEM is int
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* for 8-bit samples, INT32 for 12-bit samples. (NOTE: Floating-point DCT
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* implementations use an array of type FAST_FLOAT, instead.)
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* The DCT inputs are expected to be signed (range +-CENTERJSAMPLE).
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* The DCT outputs are returned scaled up by a factor of 8; they therefore
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* have a range of +-8K for 8-bit data, +-128K for 12-bit data. This
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* convention improves accuracy in integer implementations and saves some
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* work in floating-point ones.
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* Quantization of the output coefficients is done by jcdctmgr.c.
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*/
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#if BITS_IN_JSAMPLE == 8
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typedef int DCTELEM; /* 16 or 32 bits is fine */
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#else
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typedef INT32 DCTELEM; /* must have 32 bits */
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#endif
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typedef JMETHOD(void, forward_DCT_method_ptr, (DCTELEM * data));
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typedef JMETHOD(void, float_DCT_method_ptr, (FAST_FLOAT * data));
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/*
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* An inverse DCT routine is given a pointer to the input JBLOCK and a pointer
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* to an output sample array. The routine must dequantize the input data as
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* well as perform the IDCT; for dequantization, it uses the multiplier table
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* pointed to by compptr->dct_table. The output data is to be placed into the
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* sample array starting at a specified column. (Any row offset needed will
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* be applied to the array pointer before it is passed to the IDCT code.)
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* Note that the number of samples emitted by the IDCT routine is
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* DCT_scaled_size * DCT_scaled_size.
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*/
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/* typedef inverse_DCT_method_ptr is declared in jpegint.h */
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/*
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* Each IDCT routine has its own ideas about the best dct_table element type.
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*/
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typedef MULTIPLIER ISLOW_MULT_TYPE; /* short or int, whichever is faster */
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#if BITS_IN_JSAMPLE == 8
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typedef MULTIPLIER IFAST_MULT_TYPE; /* 16 bits is OK, use short if faster */
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#define IFAST_SCALE_BITS 2 /* fractional bits in scale factors */
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#else
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typedef INT32 IFAST_MULT_TYPE; /* need 32 bits for scaled quantizers */
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#define IFAST_SCALE_BITS 13 /* fractional bits in scale factors */
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#endif
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typedef FAST_FLOAT FLOAT_MULT_TYPE; /* preferred floating type */
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/*
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* Each IDCT routine is responsible for range-limiting its results and
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* converting them to unsigned form (0..MAXJSAMPLE). The raw outputs could
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* be quite far out of range if the input data is corrupt, so a bulletproof
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* range-limiting step is required. We use a mask-and-table-lookup method
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* to do the combined operations quickly. See the comments with
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* prepare_range_limit_table (in jdmaster.c) for more info.
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*/
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#define IDCT_range_limit(cinfo) ((cinfo)->sample_range_limit + CENTERJSAMPLE)
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#define RANGE_MASK (MAXJSAMPLE * 4 + 3) /* 2 bits wider than legal samples */
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/* Short forms of external names for systems with brain-damaged linkers. */
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#ifdef NEED_SHORT_EXTERNAL_NAMES
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#define jpeg_fdct_islow jFDislow
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#define jpeg_fdct_ifast jFDifast
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#define jpeg_fdct_float jFDfloat
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#define jpeg_idct_islow jRDislow
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#define jpeg_idct_ifast jRDifast
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#define jpeg_idct_float jRDfloat
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#define jpeg_idct_4x4 jRD4x4
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#define jpeg_idct_2x2 jRD2x2
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#define jpeg_idct_1x1 jRD1x1
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#endif /* NEED_SHORT_EXTERNAL_NAMES */
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/* Extern declarations for the forward and inverse DCT routines. */
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EXTERN void jpeg_fdct_islow JPP((DCTELEM * data));
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EXTERN void jpeg_fdct_ifast JPP((DCTELEM * data));
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EXTERN void jpeg_fdct_float JPP((FAST_FLOAT * data));
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EXTERN void jpeg_idct_islow
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JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
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JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
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EXTERN void jpeg_idct_ifast
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JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
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JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
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EXTERN void jpeg_idct_float
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JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
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JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
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EXTERN void jpeg_idct_4x4
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JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
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JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
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EXTERN void jpeg_idct_2x2
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JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
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JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
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EXTERN void jpeg_idct_1x1
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JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
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JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
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/*
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* Macros for handling fixed-point arithmetic; these are used by many
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* but not all of the DCT/IDCT modules.
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*
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* All values are expected to be of type INT32.
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* Fractional constants are scaled left by CONST_BITS bits.
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* CONST_BITS is defined within each module using these macros,
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* and may differ from one module to the next.
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*/
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#define ONE ((INT32) 1)
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#define CONST_SCALE (ONE << CONST_BITS)
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/* Convert a positive real constant to an integer scaled by CONST_SCALE.
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* Caution: some C compilers fail to reduce "FIX(constant)" at compile time,
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* thus causing a lot of useless floating-point operations at run time.
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*/
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#define FIX(x) ((INT32) ((x) * CONST_SCALE + 0.5))
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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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*/
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#define DESCALE(x,n) RIGHT_SHIFT((x) + (ONE << ((n)-1)), n)
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/* Multiply an INT32 variable by an INT32 constant to yield an INT32 result.
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* This macro is used only when the two inputs will actually be no more than
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* 16 bits wide, so that a 16x16->32 bit multiply can be used instead of a
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* full 32x32 multiply. This provides a useful speedup on many machines.
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* Unfortunately there is no way to specify a 16x16->32 multiply portably
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* in C, but some C compilers will do the right thing if you provide the
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* correct combination of casts.
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*/
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#ifdef SHORTxSHORT_32 /* may work if 'int' is 32 bits */
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#define MULTIPLY16C16(var,const) (((INT16) (var)) * ((INT16) (const)))
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#endif
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#ifdef SHORTxLCONST_32 /* known to work with Microsoft C 6.0 */
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#define MULTIPLY16C16(var,const) (((INT16) (var)) * ((INT32) (const)))
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#endif
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#ifndef MULTIPLY16C16 /* default definition */
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#define MULTIPLY16C16(var,const) ((var) * (const))
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#endif
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/* Same except both inputs are variables. */
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#ifdef SHORTxSHORT_32 /* may work if 'int' is 32 bits */
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#define MULTIPLY16V16(var1,var2) (((INT16) (var1)) * ((INT16) (var2)))
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#endif
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#ifndef MULTIPLY16V16 /* default definition */
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#define MULTIPLY16V16(var1,var2) ((var1) * (var2))
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#endif
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