#ifndef lint
static const char RCSid[] = "$Id: tcos.c,v 3.2 2003/02/22 02:07:22 greg Exp $";
#endif
/*
* Table-based cosine approximation.
*
* Use doubles in table even though we're not nearly that accurate just
* to avoid conversion and guarantee that tsin(x)^2 + tcos(x)^2 == 1.
*
* No interpolation in this version.
*
* External symbols declared in standard.h
*/
/* ====================================================================
* The Radiance Software License, Version 1.0
*
* Copyright (c) 1990 - 2002 The Regents of the University of California,
* through Lawrence Berkeley National Laboratory. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
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*
* 1. Redistributions of source code must retain the above copyright
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* if any, must include the following acknowledgment:
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* (http://radsite.lbl.gov/)
* developed by the Lawrence Berkeley National Laboratory
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#include
#ifndef NCOSENTRY
#define NCOSENTRY 256
#endif
#ifdef M_PI
#define PI ((double)M_PI)
#else
#define PI 3.14159265358979323846
#endif
double
tcos(x) /* approximate cosine */
register double x;
{
static double costab[NCOSENTRY+1];
register int i;
if (costab[0] < 0.5) /* initialize table */
for (i = 0; i <= NCOSENTRY; i++)
costab[i] = cos((PI/2./NCOSENTRY)*i);
/* normalize angle */
if (x < 0.)
x = -x;
i = (NCOSENTRY*2./PI) * x + 0.5;
if (i >= 4*NCOSENTRY)
i %= 4*NCOSENTRY;
switch (i / NCOSENTRY) {
case 0:
return(costab[i]);
case 1:
return(-costab[(2*NCOSENTRY)-i]);
case 2:
return(-costab[i-(2*NCOSENTRY)]);
case 3:
return(costab[(4*NCOSENTRY)-i]);
}
return(0.); /* should never be reached */
}