cosf.c
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/*
=============================================================================
Copyright (C) 1997-1999 NINTENDO Co.,Ltd.
$RCSfile: cosf.c,v $
$Revision: 1.1.1.1 $
$Date: 2002/10/30 02:07:09 $
=============================================================================
関数名：_ncosf
-----------------------------------------------------------------------------
書式： #include <math.h>
float _ncosf(float t)
引数： t ラディアン角
戻り値：コサイン
説明： 引数 ｔ からコサインを求めます。
cos(t) = (t^0/0!) - (t^2/2!) + (t^4/4!) - (t^6/6!)
+- ... t^(2n)/(2n)!
cos(t) = 1 - t^2/2 + t^4 * (1/4! + t^2 * (-1/6! + t^2 * (1/8! +.....
-----------------------------------------------------------------------------
*/
#include "math.h"
#define C0 (-0.5 ) /* -1/(2!) 1*/
#define C1 ( 4.166666666667e-2 ) /* 1/(4!) 24*/
#define C2 (-1.388888888889e-3 ) /* -1/(6!) 720*/
#define C3 ( 2.480158730159e-5 ) /* 1/(8!) 40320*/
#define C4 (-2.755731922399e-7 ) /* -1/(10!) 3628800*/
#define C5 ( 2.087675698787e-9 ) /* 1/(12!) 479001600*/
#define C6 (-1.147074559773e-11 ) /* -1/(14!) 87178291200*/
#define C7 ( 4.779477332387e-14 ) /* 1/(16!) */
float _ncosf(float t)
{
float q, qq;
long tn;
tn = (t / FVAL_PI) + ((t>=0) ? 0.5 : -0.5);
t = t - tn * FVAL_PI;
q = t * t;
qq = q * q * (C1 + q * (C2 + q * (C3 + q * (C4 + q * (C5 + q * (C6 + q * C7))))));
t = 1.0 - (q / 2) + qq;
if (tn & 0x01) return -t;
else return t;
}