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153 lines
6.3 KiB
153 lines
6.3 KiB
/*****************************************************************************
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* vdec_idct.h : types for the inverse discrete cosine transform
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* (c)1999 VideoLAN
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*****************************************************************************
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*****************************************************************************
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* Requires:
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* "config.h"
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* "common.h"
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* "vlc_thread.h"
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* "video_parser.h"
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*****************************************************************************/
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/*****************************************************************************
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* Common declarations
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*****************************************************************************/
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#ifndef VDEC_DFT
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typedef short dctelem_t;
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#else
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typedef int dctelem_t;
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#endif
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struct vdec_thread_s;
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#define SPARSE_SCALE_FACTOR 8
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#define DCTSIZE 8 /* 8*8 DCT */
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/*****************************************************************************
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* Macros
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*****************************************************************************/
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/* We assume that right shift corresponds to signed division by 2 with
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* rounding towards minus infinity. This is correct for typical "arithmetic
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* shift" instructions that shift in copies of the sign bit. But some
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* C compilers implement >> with an unsigned shift. For these machines you
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* must define RIGHT_SHIFT_IS_UNSIGNED.
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* RIGHT_SHIFT provides a proper signed right shift of an s32 quantity.
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* It is only applied with constant shift counts. SHIFT_TEMPS must be
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* included in the variables of any routine using RIGHT_SHIFT.
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*/
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#ifdef RIGHT_SHIFT_IS_UNSIGNED
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#define SHIFT_TEMPS s32 shift_temp;
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#define RIGHT_SHIFT(x,shft) \
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((shift_temp = (x)) < 0 ? \
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(shift_temp >> (shft)) | ((~((s32) 0)) << (32-(shft))) : \
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(shift_temp >> (shft)))
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#else
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#define SHIFT_TEMPS
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#define RIGHT_SHIFT(x,shft) ((x) >> (shft))
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#endif
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/*
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* A 2-D IDCT can be done by 1-D IDCT on each row followed by 1-D IDCT
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* on each column. Direct algorithms are also available, but they are
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* much more complex and seem not to be any faster when reduced to code.
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*
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* The poop on this scaling stuff is as follows:
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*
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* Each 1-D IDCT step produces outputs which are a factor of sqrt(N)
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* larger than the true IDCT outputs. The final outputs are therefore
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* a factor of N larger than desired; since N=8 this can be cured by
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* a simple right shift at the end of the algorithm. The advantage of
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* this arrangement is that we save two multiplications per 1-D IDCT,
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* because the y0 and y4 inputs need not be divided by sqrt(N).
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*
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* We have to do addition and subtraction of the integer inputs, which
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* is no problem, and multiplication by fractional constants, which is
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* a problem to do in integer arithmetic. We multiply all the constants
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* by CONST_SCALE and convert them to integer constants (thus retaining
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* CONST_BITS bits of precision in the constants). After doing a
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* multiplication we have to divide the product by CONST_SCALE, with proper
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* rounding, to produce the correct output. This division can be done
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* cheaply as a right shift of CONST_BITS bits. We postpone shifting
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* as long as possible so that partial sums can be added together with
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* full fractional precision.
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*
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* The outputs of the first pass are scaled up by PASS1_BITS bits so that
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* they are represented to better-than-integral precision. These outputs
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* require BITS_IN_JSAMPLE + PASS1_BITS + 3 bits; this fits in a 16-bit word
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* with the recommended scaling. (To scale up 12-bit sample data further, an
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* intermediate s32 array would be needed.)
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*
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* To avoid overflow of the 32-bit intermediate results in pass 2, we must
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* have BITS_IN_JSAMPLE + CONST_BITS + PASS1_BITS <= 26. Error analysis
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* shows that the values given below are the most effective.
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*/
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#define CONST_BITS 8 /* Jimmy chose this constant :) */
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#ifdef EIGHT_BIT_SAMPLES
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#define PASS1_BITS 2
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#else
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#define PASS1_BITS 1 /* lose a little precision to avoid overflow */
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#endif
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#define ONE ((s32) 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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* IMPORTANT: if your compiler doesn't do this arithmetic at compile time,
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* you will pay a significant penalty in run time. In that case, figure
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* the correct integer constant values and insert them by hand.
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*/
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#define FIX(x) ((s32) ((x) * CONST_SCALE + 0.5))
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/* When adding two opposite-signed fixes, the 0.5 cancels */
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#define FIX2(x) ((s32) ((x) * CONST_SCALE))
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/* Descale and correctly round an s32 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 s32 variable by an s32 constant to yield an s32 result.
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* For 8-bit samples with the recommended scaling, all the variable
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* and constant values involved are no more than 16 bits wide, so a
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* 16x16->32 bit multiply can be used instead of a full 32x32 multiply;
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* this provides a useful speedup on many machines.
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* There is no way to specify a 16x16->32 multiply in portable C, but
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* some C compilers will do the right thing if you provide the correct
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* combination of casts.
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* NB: for 12-bit samples, a full 32-bit multiplication will be needed.
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*/
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#ifdef EIGHT_BIT_SAMPLES
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#ifdef SHORTxSHORT_32 /* may work if 'int' is 32 bits */
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#define MULTIPLY(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 MULTIPLY(var,const) (((INT16) (var)) * ((s32) (const)))
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#endif
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#endif
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#ifndef MULTIPLY /* default definition */
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#define MULTIPLY(var,const) ((var) * (const))
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#endif
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/*****************************************************************************
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* Function pointers
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*****************************************************************************/
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typedef void (*f_idct_t)( struct vdec_thread_s *, dctelem_t*, int );
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/*****************************************************************************
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* Prototypes
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*****************************************************************************/
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void vdec_InitIDCT (struct vdec_thread_s * p_vdec);
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void vdec_SparseIDCT( struct vdec_thread_s *, dctelem_t*, int );
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void vdec_IDCT( struct vdec_thread_s *, dctelem_t*, int );
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