tomwalters@0: /*
tomwalters@0:     Copyright (c) Applied Psychology Unit, Medical Research Council. 1988, 1989
tomwalters@0:     ===========================================================================
tomwalters@0: 
tomwalters@0:     Permission to use, copy, modify, and distribute this software without fee 
tomwalters@0:     is hereby granted for research purposes, provided that this copyright 
tomwalters@0:     notice appears in all copies and in all supporting documentation, and that 
tomwalters@0:     the software is not redistributed for any fee (except for a nominal shipping 
tomwalters@0:     charge). Anyone wanting to incorporate all or part of this software in a
tomwalters@0:     commercial product must obtain a license from the Medical Research Council.
tomwalters@0: 
tomwalters@0:     The MRC makes no representations about the suitability of this 
tomwalters@0:     software for any purpose.  It is provided "as is" without express or implied 
tomwalters@0:     warranty.
tomwalters@0:  
tomwalters@0:     THE MRC DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING 
tomwalters@0:     ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL THE
tomwalters@0:     A.P.U. BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY 
tomwalters@0:     DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN 
tomwalters@0:     AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 
tomwalters@0:     OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
tomwalters@0: */
tomwalters@0: 
tomwalters@0: /*
tomwalters@0:     interp.c
tomwalters@0:     ========
tomwalters@0: 
tomwalters@0:     Some types of interpolation of short arrays for multiplexed filters
tomwalters@0: 
tomwalters@0:     linterp() performs fast linear interpolations from n points to n*2-1
tomwalters@0:     points repeatedly till the number of points required is reached.
tomwalters@0: 
tomwalters@0:     interp() performs a slower but hopefully smoother (in the first differential)
tomwalters@0:     interpolation from n points to n*2-1 points.
tomwalters@0: 
tomwalters@0:     Author  : John Holdsworth
tomwalters@0:     Written : 11th March, 1989.
tomwalters@0: 
tomwalters@0:     Edited  :
tomwalters@0: 
tomwalters@0: 
tomwalters@0: 
tomwalters@0: 
tomwalters@0: */
tomwalters@0: 
tomwalters@0: 
tomwalters@0: #ifndef  lint
tomwalters@0: static char *sccs_id = "@(#)interp.c	1.4     J. Holdsworth (MRC-APU)  11/21/89" ;
tomwalters@0: #endif
tomwalters@0: 
tomwalters@0: 
tomwalters@0: /* linear interpolation */
tomwalters@0: 
tomwalters@0: int linterp( input, output, points, newpoints )
tomwalters@0: short *input, *output ;
tomwalters@0: int points, newpoints ;
tomwalters@0: {
tomwalters@0:     register int store ;
tomwalters@0:     register short *optr, *end, *iptr ;
tomwalters@0:     register int nextpoints ;
tomwalters@0: 
tomwalters@0:     nextpoints = points ;
tomwalters@0:     end = input + 1 ;
tomwalters@0: 
tomwalters@0:     do {
tomwalters@0: 
tomwalters@0: 	iptr = end - 1 + nextpoints - 1 ;
tomwalters@0: 
tomwalters@0: 	nextpoints = nextpoints * 2 - 1 ;
tomwalters@0: 
tomwalters@0: 	optr = output + nextpoints ;
tomwalters@0: 	end  = output + 1 ;
tomwalters@0: 
tomwalters@0: 	do {
tomwalters@0: 	    *--optr = store = *  iptr ;
tomwalters@0: 	    *--optr = store + *--iptr >> 1 ;
tomwalters@0: 	} while( optr > end ) ;
tomwalters@0: 
tomwalters@0:     } while ( nextpoints < newpoints ) ;
tomwalters@0: 
tomwalters@0:     *--optr = *iptr ;
tomwalters@0: 
tomwalters@0:     return ;
tomwalters@0: }
tomwalters@0: 
tomwalters@0: /* simple 2nd orderish interpolation - preserves slopes */
tomwalters@0: 
tomwalters@0: int interp( input, output, points, newpoints )
tomwalters@0: short *input, *output ;
tomwalters@0: int points, newpoints ;
tomwalters@0: {
tomwalters@0:     register short *optr, *end, *iptr ;
tomwalters@0:     register int nextnum, bignum, oldbignum, oldput ;
tomwalters@0: 
tomwalters@0:     iptr = input  ;
tomwalters@0:     optr = output ;
tomwalters@0:     end  = output + newpoints ;
tomwalters@0: 
tomwalters@0: #ifdef lint
tomwalters@0:     points ;
tomwalters@0: #endif
tomwalters@0: 
tomwalters@0:     nextnum   = *(iptr+1) ;
tomwalters@0:     oldbignum = ( *iptr << 2 ) + *iptr   ;
tomwalters@0:     oldput    = ( *iptr << 1 ) - nextnum ;
tomwalters@0: 
tomwalters@0:     while( optr < end ) {
tomwalters@0: 	*optr++ = *iptr++ ;
tomwalters@0: 	if( optr < end ) {
tomwalters@0: 	    bignum = ( nextnum << 2 ) + nextnum ;
tomwalters@0: 	    if( optr < end - 2 )
tomwalters@0: 		nextnum = *(iptr+1) ;
tomwalters@0: 	    else
tomwalters@0: 		nextnum = ( *iptr << 1 ) - *(iptr-1) ;
tomwalters@0: 	    *optr++ = ( oldbignum + bignum - oldput - nextnum + 4 ) >> 3 ;
tomwalters@0: 	    oldbignum = bignum ;
tomwalters@0: 	    oldput = *(iptr-1) ;
tomwalters@0: 	}
tomwalters@0:     }
tomwalters@0: 
tomwalters@0:     return ;
tomwalters@0: }
tomwalters@0: