text: /*
   * jdct.h
   *
   * Copyright (C) 1994-1996, Thomas G. Lane.
   * This file is part of the Independent JPEG Group's software.
   * For conditions of distribution and use, see the accompanying README file.
   *
   * This include file contains common declarations for the forward and
   * inverse DCT modules.  These declarations are private to the DCT managers
   * (jcdctmgr.c, jddctmgr.c) and the individual DCT algorithms.
   * The individual DCT algorithms are kept in separate files to ease 
   * machine-dependent tuning (e.g., assembly coding).
   */
  
  
  /*
   * A forward DCT routine is given a pointer to a work area of type DCTELEM[];
   * the DCT is to be performed in-place in that buffer.  Type DCTELEM is int
   * for 8-bit samples, IJG_INT32 for 12-bit samples.  (NOTE: Floating-point DCT
   * implementations use an array of type FAST_FLOAT, instead.)
   * The DCT inputs are expected to be signed (range +-CENTERJSAMPLE).
   * The DCT outputs are returned scaled up by a factor of 8; they therefore
   * have a range of +-8K for 8-bit data, +-128K for 12-bit data.  This
   * convention improves accuracy in integer implementations and saves some
   * work in floating-point ones.
   * Quantization of the output coefficients is done by jcdctmgr.c.
   */
  
  #if BITS_IN_JSAMPLE == 8
  typedef int DCTELEM;		/* 16 or 32 bits is fine */
  #else
  typedef IJG_INT32 DCTELEM;		/* must have 32 bits */
  #endif
  
  typedef JMETHOD(void, forward_DCT_method_ptr, (DCTELEM * data));
  typedef JMETHOD(void, float_DCT_method_ptr, (FAST_FLOAT * data));
  
  
  /*
   * An inverse DCT routine is given a pointer to the input JBLOCK and a pointer
   * to an output sample array.  The routine must dequantize the input data as
   * well as perform the IDCT; for dequantization, it uses the multiplier table
   * pointed to by compptr->dct_table.  The output data is to be placed into the
   * sample array starting at a specified column.  (Any row offset needed will
   * be applied to the array pointer before it is passed to the IDCT code.)
   * Note that the number of samples emitted by the IDCT routine is
   * DCT_scaled_size * DCT_scaled_size.
   */
  
  /* typedef inverse_DCT_method_ptr is declared in jpegint.h */
  
  /*
   * Each IDCT routine has its own ideas about the best dct_table element type.
   */
  
  typedef MULTIPLIER ISLOW_MULT_TYPE; /* short or int, whichever is faster */
  #if BITS_IN_JSAMPLE == 8
  typedef MULTIPLIER IFAST_MULT_TYPE; /* 16 bits is OK, use short if faster */
  #define IFAST_SCALE_BITS  2	/* fractional bits in scale factors */
  #else
  typedef IJG_INT32 IFAST_MULT_TYPE;	/* need 32 bits for scaled quantizers */
  #define IFAST_SCALE_BITS  13	/* fractional bits in scale factors */
  #endif
  typedef FAST_FLOAT FLOAT_MULT_TYPE; /* preferred floating type */
  
  
  /*
   * Each IDCT routine is responsible for range-limiting its results and
   * converting them to unsigned form (0..MAXJSAMPLE).  The raw outputs could
   * be quite far out of range if the input data is corrupt, so a bulletproof
   * range-limiting step is required.  We use a mask-and-table-lookup method
   * to do the combined operations quickly.  See the comments with
   * prepare_range_limit_table (in jdmaster.c) for more info.
   */
  
  #define IDCT_range_limit(cinfo)  ((cinfo)->sample_range_limit + CENTERJSAMPLE)
  
  #define RANGE_MASK  (MAXJSAMPLE * 4 + 3) /* 2 bits wider than legal samples */
  
  
  /* Short forms of external names for systems with brain-damaged linkers. */
  
  #ifdef NEED_SHORT_EXTERNAL_NAMES
  #define jpeg_fdct_islow		jpeg16_fdct_islow
  #define jpeg_fdct_ifast		jpeg16_fdct_ifast
  #define jpeg_fdct_float		jpeg16_fdct_float
  #define jpeg_idct_islow		jpeg16_idct_islow
  #define jpeg_idct_ifast		jpeg16_idct_ifast
  #define jpeg_idct_float		jpeg16_idct_float
  #define jpeg_idct_4x4		jpeg16_idct_4x4
  #define jpeg_idct_2x2		jpeg16_idct_2x2
  #define jpeg_idct_1x1		jpeg16_idct_1x1
  #endif /* NEED_SHORT_EXTERNAL_NAMES */
  
  /* Extern declarations for the forward and inverse DCT routines. */
  
  EXTERN(void) jpeg_fdct_islow JPP((DCTELEM * data));
  EXTERN(void) jpeg_fdct_ifast JPP((DCTELEM * data));
  EXTERN(void) jpeg_fdct_float JPP((FAST_FLOAT * data));
  
  EXTERN(void) jpeg_idct_islow
      JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
  	 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
  EXTERN(void) jpeg_idct_ifast
      JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
  	 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
  EXTERN(void) jpeg_idct_float
      JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
  	 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
  EXTERN(void) jpeg_idct_4x4
      JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
  	 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
  EXTERN(void) jpeg_idct_2x2
      JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
  	 JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
  EXTERN(void) jpeg_idct_1x1
      JPP((j_decompress_ptr cinfo, jpeg_component_info * compptr,
  	 const JCOEFPTR coef_block, JSAMPARRAY output_buf, JDIMENSION output_col));
  
  
  /*
   * Macros for handling fixed-point arithmetic; these are used by many
   * but not all of the DCT/IDCT modules.
   *
   * All values are expected to be of type IJG_INT32.
   * Fractional constants are scaled left by CONST_BITS bits.
   * CONST_BITS is defined within each module using these macros,
   * and may differ from one module to the next.
   */
  
  #define ONE	((IJG_INT32) 1)
  #define CONST_SCALE (ONE << CONST_BITS)
  
  /* Convert a positive real constant to an integer scaled by CONST_SCALE.
   * Caution: some C compilers fail to reduce "FIX(constant)" at compile time,
   * thus causing a lot of useless floating-point operations at run time.
   */
  
  #define FIX(x)	((IJG_INT32) ((x) * CONST_SCALE + 0.5))
  
  /* Descale and correctly round an IJG_INT32 value that's scaled by N bits.
   * We assume RIGHT_SHIFT rounds towards minus infinity, so adding
   * the fudge factor is correct for either sign of X.
   */
  
  #define DESCALE(x,n)  RIGHT_SHIFT((x) + (ONE << ((n)-1)), n)
  
  /* Multiply an IJG_INT32 variable by an IJG_INT32 constant to yield an IJG_INT32 result.
   * This macro is used only when the two inputs will actually be no more than
   * 16 bits wide, so that a 16x16->32 bit multiply can be used instead of a
   * full 32x32 multiply.  This provides a useful speedup on many machines.
   * Unfortunately there is no way to specify a 16x16->32 multiply portably
   * in C, but some C compilers will do the right thing if you provide the
   * correct combination of casts.
   */
  
  #ifdef SHORTxSHORT_32		/* may work if 'int' is 32 bits */
  #define MULTIPLY16C16(var,const)  (((INT16) (var)) * ((INT16) (const)))
  #endif
  #ifdef SHORTxLCONST_32		/* known to work with Microsoft C 6.0 */
  #define MULTIPLY16C16(var,const)  (((INT16) (var)) * ((IJG_INT32) (const)))
  #endif
  
  #ifndef MULTIPLY16C16		/* default definition */
  #define MULTIPLY16C16(var,const)  ((var) * (const))
  #endif
  
  /* Same except both inputs are variables. */
  
  #ifdef SHORTxSHORT_32		/* may work if 'int' is 32 bits */
  #define MULTIPLY16V16(var1,var2)  (((INT16) (var1)) * ((INT16) (var2)))
  #endif
  
  #ifndef MULTIPLY16V16		/* default definition */
  #define MULTIPLY16V16(var1,var2)  ((var1) * (var2))
  #endif
  