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jdct.h (7041B)


      1 /*
      2  * jdct.h
      3  *
      4  * Copyright (C) 1994-1996, Thomas G. Lane.
      5  * This file is part of the Independent JPEG Group's software.
      6  * For conditions of distribution and use, see the accompanying README file.
      7  *
      8  * This include file contains common declarations for the forward and
      9  * inverse DCT modules.  These declarations are private to the DCT managers
     10  * (jcdctmgr.c, jddctmgr.c) and the individual DCT algorithms.
     11  * The individual DCT algorithms are kept in separate files to ease 
     12  * machine-dependent tuning (e.g., assembly coding).
     13  */
     14 
     15 
     16 /*
     17  * A forward DCT routine is given a pointer to a work area of type DCTELEM[];
     18  * the DCT is to be performed in-place in that buffer.  Type DCTELEM is int
     19  * for 8-bit samples, INT32 for 12-bit samples.  (NOTE: Floating-point DCT
     20  * implementations use an array of type FAST_FLOAT, instead.)
     21  * The DCT inputs are expected to be signed (range +-CENTERJSAMPLE).
     22  * The DCT outputs are returned scaled up by a factor of 8; they therefore
     23  * have a range of +-8K for 8-bit data, +-128K for 12-bit data.  This
     24  * convention improves accuracy in integer implementations and saves some
     25  * work in floating-point ones.
     26  * Quantization of the output coefficients is done by jcdctmgr.c.
     27  */
     28 
     29 #if BITS_IN_JSAMPLE == 8
     30 typedef int DCTELEM;		/* 16 or 32 bits is fine */
     31 #else
     32 typedef INT32 DCTELEM;		/* must have 32 bits */
     33 #endif
     34 
     35 typedef JMETHOD(void, forward_DCT_method_ptr, (DCTELEM * data));
     36 typedef JMETHOD(void, float_DCT_method_ptr, (FAST_FLOAT * data));
     37 
     38 
     39 /*
     40  * An inverse DCT routine is given a pointer to the input JBLOCK and a pointer
     41  * to an output sample array.  The routine must dequantize the input data as
     42  * well as perform the IDCT; for dequantization, it uses the multiplier table
     43  * pointed to by compptr->dct_table.  The output data is to be placed into the
     44  * sample array starting at a specified column.  (Any row offset needed will
     45  * be applied to the array pointer before it is passed to the IDCT code.)
     46  * Note that the number of samples emitted by the IDCT routine is
     47  * DCT_scaled_size * DCT_scaled_size.
     48  */
     49 
     50 /* typedef inverse_DCT_method_ptr is declared in jpegint.h */
     51 
     52 /*
     53  * Each IDCT routine has its own ideas about the best dct_table element type.
     54  */
     55 
     56 typedef MULTIPLIER ISLOW_MULT_TYPE; /* short or int, whichever is faster */
     57 #if BITS_IN_JSAMPLE == 8
     58 typedef MULTIPLIER IFAST_MULT_TYPE; /* 16 bits is OK, use short if faster */
     59 #define IFAST_SCALE_BITS  2	/* fractional bits in scale factors */
     60 #else
     61 typedef INT32 IFAST_MULT_TYPE;	/* need 32 bits for scaled quantizers */
     62 #define IFAST_SCALE_BITS  13	/* fractional bits in scale factors */
     63 #endif
     64 typedef FAST_FLOAT FLOAT_MULT_TYPE; /* preferred floating type */
     65 
     66 
     67 /*
     68  * Each IDCT routine is responsible for range-limiting its results and
     69  * converting them to unsigned form (0..MAXJSAMPLE).  The raw outputs could
     70  * be quite far out of range if the input data is corrupt, so a bulletproof
     71  * range-limiting step is required.  We use a mask-and-table-lookup method
     72  * to do the combined operations quickly.  See the comments with
     73  * prepare_range_limit_table (in jdmaster.c) for more info.
     74  */
     75 
     76 #define IDCT_range_limit(cinfo)  ((cinfo)->sample_range_limit + CENTERJSAMPLE)
     77 
     78 #define RANGE_MASK  (MAXJSAMPLE * 4 + 3) /* 2 bits wider than legal samples */
     79 
     80 
     81 /* Short forms of external names for systems with brain-damaged linkers. */
     82 
     83 #ifdef NEED_SHORT_EXTERNAL_NAMES
     84 #define jpeg_fdct_islow		jFDislow
     85 #define jpeg_fdct_ifast		jFDifast
     86 #define jpeg_fdct_float		jFDfloat
     87 #define jpeg_idct_islow		jRDislow
     88 #define jpeg_idct_ifast		jRDifast
     89 #define jpeg_idct_float		jRDfloat
     90 #define jpeg_idct_4x4		jRD4x4
     91 #define jpeg_idct_2x2		jRD2x2
     92 #define jpeg_idct_1x1		jRD1x1
     93 #endif /* NEED_SHORT_EXTERNAL_NAMES */
     94 
     95 /* Extern declarations for the forward and inverse DCT routines. */
     96 
     97 EXTERN(void) jpeg_fdct_islow JPP((DCTELEM * data));
     98 EXTERN(void) jpeg_fdct_ifast JPP((DCTELEM * data));
     99 EXTERN(void) jpeg_fdct_float JPP((FAST_FLOAT * data));
    100 
    101 EXTERN(void) jpeg_idct_islow
    102     JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
    103 	 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
    104 EXTERN(void) jpeg_idct_ifast
    105     JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
    106 	 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
    107 EXTERN(void) jpeg_idct_float
    108     JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
    109 	 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
    110 EXTERN(void) jpeg_idct_4x4
    111     JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
    112 	 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
    113 EXTERN(void) jpeg_idct_2x2
    114     JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
    115 	 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
    116 EXTERN(void) jpeg_idct_1x1
    117     JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
    118 	 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
    119 
    120 
    121 /*
    122  * Macros for handling fixed-point arithmetic; these are used by many
    123  * but not all of the DCT/IDCT modules.
    124  *
    125  * All values are expected to be of type INT32.
    126  * Fractional constants are scaled left by CONST_BITS bits.
    127  * CONST_BITS is defined within each module using these macros,
    128  * and may differ from one module to the next.
    129  */
    130 
    131 #define ONE	((INT32) 1)
    132 #define CONST_SCALE (ONE << CONST_BITS)
    133 
    134 /* Convert a positive real constant to an integer scaled by CONST_SCALE.
    135  * Caution: some C compilers fail to reduce "FIX(constant)" at compile time,
    136  * thus causing a lot of useless floating-point operations at run time.
    137  */
    138 
    139 #define FIX(x)	((INT32) ((x) * CONST_SCALE + 0.5))
    140 
    141 /* Descale and correctly round an INT32 value that's scaled by N bits.
    142  * We assume RIGHT_SHIFT rounds towards minus infinity, so adding
    143  * the fudge factor is correct for either sign of X.
    144  */
    145 
    146 #define DESCALE(x,n)  RIGHT_SHIFT((x) + (ONE << ((n)-1)), n)
    147 
    148 /* Multiply an INT32 variable by an INT32 constant to yield an INT32 result.
    149  * This macro is used only when the two inputs will actually be no more than
    150  * 16 bits wide, so that a 16x16->32 bit multiply can be used instead of a
    151  * full 32x32 multiply.  This provides a useful speedup on many machines.
    152  * Unfortunately there is no way to specify a 16x16->32 multiply portably
    153  * in C, but some C compilers will do the right thing if you provide the
    154  * correct combination of casts.
    155  */
    156 
    157 #ifdef SHORTxSHORT_32		/* may work if 'int' is 32 bits */
    158 #define MULTIPLY16C16(var,const)  (((INT16) (var)) * ((INT16) (const)))
    159 #endif
    160 #ifdef SHORTxLCONST_32		/* known to work with Microsoft C 6.0 */
    161 #define MULTIPLY16C16(var,const)  (((INT16) (var)) * ((INT32) (const)))
    162 #endif
    163 
    164 #ifndef MULTIPLY16C16		/* default definition */
    165 #define MULTIPLY16C16(var,const)  ((var) * (const))
    166 #endif
    167 
    168 /* Same except both inputs are variables. */
    169 
    170 #ifdef SHORTxSHORT_32		/* may work if 'int' is 32 bits */
    171 #define MULTIPLY16V16(var1,var2)  (((INT16) (var1)) * ((INT16) (var2)))
    172 #endif
    173 
    174 #ifndef MULTIPLY16V16		/* default definition */
    175 #define MULTIPLY16V16(var1,var2)  ((var1) * (var2))
    176 #endif