/***********************************************************************
   (C) Copyright, 1990 by Dean Rubine, Carnegie Mellon University
    Permission to use this code for noncommercial purposes is hereby granted.
    Permission to copy and distribute this code is hereby granted provided
    this copyright notice is retained.  All other rights reserved.
 **********************************************************************/

#include <stdio.h>
#include "util.h"
#include "functab.h"

/*
 Format of a function table:

	name npoints minx maxx
	y1 y2 ...
 */


static
FuncTab
NewFuncTab(name, npoints, minx, maxx)
char *name;
int npoints;
double minx, maxx;
{
	register FuncTab ft = allocate(1, struct functab);
	ft->name = scopy(name);
	ft->n = npoints;
	ft->points = allocate(ft->n, double);
	if(maxx < minx + 1.0e-5)
		error("%s: maxx %g < minx %g + 1.0e-5", 
		      ft->name, maxx, minx);
	if(ft->n <= 1)
		error("%s: too few points %d", ft->name, ft->n);
	ft->scale = (ft->n - 1) / (maxx - minx) ;
	ft->offset = -minx * ft->scale + 0.5;	/* .5 for rounding */
	return ft;
}

FuncTab
ReadFuncTab(f)
FILE *f;
{
	register FuncTab ft;
	char name[50];
	int npoints;
	double minx, maxx;
	double y;
	register int i;

	if(fscanf(f, "%s %d %lf %lf", name, npoints, &minx, &maxx) != 4)
		error("ReadFuncTab: bad header");
	ft = NewFuncTab(name, npoints, minx, maxx);
	for(i = 0; i < ft->n; i++) {
		if(fscanf(f, "%lf", &y) != 1)
			error("%s: Error reading %d'th point", ft->name, i);
		ft->points[i] = y;
	}
	return ft;
}

FuncTab
GenFuncTab(name, npoints, minx, maxx, f)
char *name;
int npoints;
double minx, maxx;
double (*f)();
{
	register int i;
	register FuncTab ft = NewFuncTab(name, npoints, minx, maxx);
	for(i = 0; i < npoints; i++)
		ft->points[i] = (*f)(minx + (i*(maxx-minx))/(npoints-1));
	return ft;
}

double
EvalFuncTab(ft, x)
register FuncTab ft;
double x;
{
	int index = ft->scale * x + ft->offset;
	if(index < 0 || index >= ft->n)
		error("%s(%g): index=%d n=%d", ft->name, x, index, ft->n);
	return ft->points[index];
}