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plt-scheme  4.2.1
jdct.h
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00001 /*
00002  * jdct.h
00003  *
00004  * Copyright (C) 1994-1996, Thomas G. Lane.
00005  * This file is part of the Independent JPEG Group's software.
00006  * For conditions of distribution and use, see the accompanying README file.
00007  *
00008  * This include file contains common declarations for the forward and
00009  * inverse DCT modules.  These declarations are private to the DCT managers
00010  * (jcdctmgr.c, jddctmgr.c) and the individual DCT algorithms.
00011  * The individual DCT algorithms are kept in separate files to ease 
00012  * machine-dependent tuning (e.g., assembly coding).
00013  */
00014 
00015 
00016 /*
00017  * A forward DCT routine is given a pointer to a work area of type DCTELEM[];
00018  * the DCT is to be performed in-place in that buffer.  Type DCTELEM is int
00019  * for 8-bit samples, INT32 for 12-bit samples.  (NOTE: Floating-point DCT
00020  * implementations use an array of type FAST_FLOAT, instead.)
00021  * The DCT inputs are expected to be signed (range +-CENTERJSAMPLE).
00022  * The DCT outputs are returned scaled up by a factor of 8; they therefore
00023  * have a range of +-8K for 8-bit data, +-128K for 12-bit data.  This
00024  * convention improves accuracy in integer implementations and saves some
00025  * work in floating-point ones.
00026  * Quantization of the output coefficients is done by jcdctmgr.c.
00027  */
00028 
00029 #if BITS_IN_JSAMPLE == 8
00030 typedef int DCTELEM;        /* 16 or 32 bits is fine */
00031 #else
00032 typedef INT32 DCTELEM;             /* must have 32 bits */
00033 #endif
00034 
00035 typedef JMETHOD(void, forward_DCT_method_ptr, (DCTELEM * data));
00036 typedef JMETHOD(void, float_DCT_method_ptr, (FAST_FLOAT * data));
00037 
00038 
00039 /*
00040  * An inverse DCT routine is given a pointer to the input JBLOCK and a pointer
00041  * to an output sample array.  The routine must dequantize the input data as
00042  * well as perform the IDCT; for dequantization, it uses the multiplier table
00043  * pointed to by compptr->dct_table.  The output data is to be placed into the
00044  * sample array starting at a specified column.  (Any row offset needed will
00045  * be applied to the array pointer before it is passed to the IDCT code.)
00046  * Note that the number of samples emitted by the IDCT routine is
00047  * DCT_scaled_size * DCT_scaled_size.
00048  */
00049 
00050 /* typedef inverse_DCT_method_ptr is declared in jpegint.h */
00051 
00052 /*
00053  * Each IDCT routine has its own ideas about the best dct_table element type.
00054  */
00055 
00056 typedef MULTIPLIER ISLOW_MULT_TYPE; /* short or int, whichever is faster */
00057 #if BITS_IN_JSAMPLE == 8
00058 typedef MULTIPLIER IFAST_MULT_TYPE; /* 16 bits is OK, use short if faster */
00059 #define IFAST_SCALE_BITS  2 /* fractional bits in scale factors */
00060 #else
00061 typedef INT32 IFAST_MULT_TYPE;     /* need 32 bits for scaled quantizers */
00062 #define IFAST_SCALE_BITS  13       /* fractional bits in scale factors */
00063 #endif
00064 typedef FAST_FLOAT FLOAT_MULT_TYPE; /* preferred floating type */
00065 
00066 
00067 /*
00068  * Each IDCT routine is responsible for range-limiting its results and
00069  * converting them to unsigned form (0..MAXJSAMPLE).  The raw outputs could
00070  * be quite far out of range if the input data is corrupt, so a bulletproof
00071  * range-limiting step is required.  We use a mask-and-table-lookup method
00072  * to do the combined operations quickly.  See the comments with
00073  * prepare_range_limit_table (in jdmaster.c) for more info.
00074  */
00075 
00076 #define IDCT_range_limit(cinfo)  ((cinfo)->sample_range_limit + CENTERJSAMPLE)
00077 
00078 #define RANGE_MASK  (MAXJSAMPLE * 4 + 3) /* 2 bits wider than legal samples */
00079 
00080 
00081 /* Short forms of external names for systems with brain-damaged linkers. */
00082 
00083 #ifdef NEED_SHORT_EXTERNAL_NAMES
00084 #define jpeg_fdct_islow            jFDislow
00085 #define jpeg_fdct_ifast            jFDifast
00086 #define jpeg_fdct_float            jFDfloat
00087 #define jpeg_idct_islow            jRDislow
00088 #define jpeg_idct_ifast            jRDifast
00089 #define jpeg_idct_float            jRDfloat
00090 #define jpeg_idct_4x4              jRD4x4
00091 #define jpeg_idct_2x2              jRD2x2
00092 #define jpeg_idct_1x1              jRD1x1
00093 #endif /* NEED_SHORT_EXTERNAL_NAMES */
00094 
00095 /* Extern declarations for the forward and inverse DCT routines. */
00096 
00097 EXTERN(void) jpeg_fdct_islow JPP((DCTELEM * data));
00098 EXTERN(void) jpeg_fdct_ifast JPP((DCTELEM * data));
00099 EXTERN(void) jpeg_fdct_float JPP((FAST_FLOAT * data));
00100 
00101 EXTERN(void) jpeg_idct_islow
00102     JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
00103         JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
00104 EXTERN(void) jpeg_idct_ifast
00105     JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
00106         JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
00107 EXTERN(void) jpeg_idct_float
00108     JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
00109         JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
00110 EXTERN(void) jpeg_idct_4x4
00111     JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
00112         JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
00113 EXTERN(void) jpeg_idct_2x2
00114     JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
00115         JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
00116 EXTERN(void) jpeg_idct_1x1
00117     JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
00118         JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
00119 
00120 
00121 /*
00122  * Macros for handling fixed-point arithmetic; these are used by many
00123  * but not all of the DCT/IDCT modules.
00124  *
00125  * All values are expected to be of type INT32.
00126  * Fractional constants are scaled left by CONST_BITS bits.
00127  * CONST_BITS is defined within each module using these macros,
00128  * and may differ from one module to the next.
00129  */
00130 
00131 #define ONE   ((INT32) 1)
00132 #define CONST_SCALE (ONE << CONST_BITS)
00133 
00134 /* Convert a positive real constant to an integer scaled by CONST_SCALE.
00135  * Caution: some C compilers fail to reduce "FIX(constant)" at compile time,
00136  * thus causing a lot of useless floating-point operations at run time.
00137  */
00138 
00139 #define FIX(x)       ((INT32) ((x) * CONST_SCALE + 0.5))
00140 
00141 /* Descale and correctly round an INT32 value that's scaled by N bits.
00142  * We assume RIGHT_SHIFT rounds towards minus infinity, so adding
00143  * the fudge factor is correct for either sign of X.
00144  */
00145 
00146 #define DESCALE(x,n)  RIGHT_SHIFT((x) + (ONE << ((n)-1)), n)
00147 
00148 /* Multiply an INT32 variable by an INT32 constant to yield an INT32 result.
00149  * This macro is used only when the two inputs will actually be no more than
00150  * 16 bits wide, so that a 16x16->32 bit multiply can be used instead of a
00151  * full 32x32 multiply.  This provides a useful speedup on many machines.
00152  * Unfortunately there is no way to specify a 16x16->32 multiply portably
00153  * in C, but some C compilers will do the right thing if you provide the
00154  * correct combination of casts.
00155  */
00156 
00157 #ifdef SHORTxSHORT_32              /* may work if 'int' is 32 bits */
00158 #define MULTIPLY16C16(var,const)  (((INT16) (var)) * ((INT16) (const)))
00159 #endif
00160 #ifdef SHORTxLCONST_32             /* known to work with Microsoft C 6.0 */
00161 #define MULTIPLY16C16(var,const)  (((INT16) (var)) * ((INT32) (const)))
00162 #endif
00163 
00164 #ifndef MULTIPLY16C16              /* default definition */
00165 #define MULTIPLY16C16(var,const)  ((var) * (const))
00166 #endif
00167 
00168 /* Same except both inputs are variables. */
00169 
00170 #ifdef SHORTxSHORT_32              /* may work if 'int' is 32 bits */
00171 #define MULTIPLY16V16(var1,var2)  (((INT16) (var1)) * ((INT16) (var2)))
00172 #endif
00173 
00174 #ifndef MULTIPLY16V16              /* default definition */
00175 #define MULTIPLY16V16(var1,var2)  ((var1) * (var2))
00176 #endif