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176 lines
6.9 KiB
176 lines
6.9 KiB
/* |
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* jdct.h |
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* |
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* Copyright (C) 1994-1996, 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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