1 /* @(#)s_atan.c 5.1 93/09/24 */
2 /* FreeBSD: head/lib/msun/src/s_atan.c 176451 2008-02-22 02:30:36Z das */
4 * ====================================================
5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
7 * Developed at SunPro, a Sun Microsystems, Inc. business.
8 * Permission to use, copy, modify, and distribute this
9 * software is freely granted, provided that this notice
11 * ====================================================
14 #include <sys/cdefs.h>
15 __FBSDID("$FreeBSD$");
18 * See comments in s_atan.c.
19 * Converted to long double by David Schultz <das@FreeBSD.ORG>.
26 #include "math_private.h"
28 static const long double
36 long double w,s1,s2,z;
38 int16_t expsign, expt;
42 expsign = u.xbits.expsign;
43 expt = expsign & 0x7fff;
44 if(expt >= ATAN_CONST) { /* if |x| is large, atan(x)~=pi/2 */
45 if(expt == BIAS + LDBL_MAX_EXP &&
46 ((u.bits.manh&~LDBL_NBIT)|u.bits.manl)!=0)
48 if(expsign>0) return atanhi[3]+atanlo[3];
49 else return -atanhi[3]-atanlo[3];
51 /* Extract the exponent and the first few bits of the mantissa. */
52 /* XXX There should be a more convenient way to do this. */
53 expman = (expt << 8) | ((u.bits.manh >> (MANH_SIZE - 9)) & 0xff);
54 if (expman < ((BIAS - 2) << 8) + 0xc0) { /* |x| < 0.4375 */
55 if (expt < ATAN_LINEAR) { /* if |x| is small, atanl(x)~=x */
56 if(huge+x>one) return x; /* raise inexact */
61 if (expman < (BIAS << 8) + 0x30) { /* |x| < 1.1875 */
62 if (expman < ((BIAS - 1) << 8) + 0x60) { /* 7/16 <=|x|<11/16 */
63 id = 0; x = (2.0*x-one)/(2.0+x);
64 } else { /* 11/16<=|x|< 19/16 */
65 id = 1; x = (x-one)/(x+one);
68 if (expman < ((BIAS + 1) << 8) + 0x38) { /* |x| < 2.4375 */
69 id = 2; x = (x-1.5)/(one+1.5*x);
70 } else { /* 2.4375 <= |x| < 2^ATAN_CONST */
74 /* end of argument reduction */
77 /* break sum aT[i]z**(i+1) into odd and even poly */
80 if (id<0) return x - x*(s1+s2);
82 z = atanhi[id] - ((x*(s1+s2) - atanlo[id]) - x);
83 return (expsign<0)? -z:z;