compiler/stdc/math/s_atanf.c

   1 /* s_atanf.c -- float version of s_atan.c.
   2  * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
   3  */
   4
   5 /*
   6  * ====================================================
   7  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   8  *
   9  * Developed at SunPro, a Sun Microsystems, Inc. business.
  10  * Permission to use, copy, modify, and distribute this
  11  * software is freely granted, provided that this notice
  12  * is preserved.
  13  * ====================================================
  14  */
  15
  16 #ifndef lint
  17 static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_atanf.c,v 1.10 2008/08/01 01:24:25 das Exp $";
  18 #endif
  19
  20 #include "math.h"
  21 #include "math_private.h"
  22
  23 static const float atanhi[] = {
  24   4.6364760399e-01, /* atan(0.5)hi 0x3eed6338 */
  25   7.8539812565e-01, /* atan(1.0)hi 0x3f490fda */
  26   9.8279368877e-01, /* atan(1.5)hi 0x3f7b985e */
  27   1.5707962513e+00, /* atan(inf)hi 0x3fc90fda */
  28 };
  29
  30 static const float atanlo[] = {
  31   5.0121582440e-09, /* atan(0.5)lo 0x31ac3769 */
  32   3.7748947079e-08, /* atan(1.0)lo 0x33222168 */
  33   3.4473217170e-08, /* atan(1.5)lo 0x33140fb4 */
  34   7.5497894159e-08, /* atan(inf)lo 0x33a22168 */
  35 };
  36
  37 static const float aT[] = {
  38   3.3333328366e-01,
  39  -1.9999158382e-01,
  40   1.4253635705e-01,
  41  -1.0648017377e-01,
  42   6.1687607318e-02,
  43 };
  44
  45 static const float
  46 one   = 1.0,
  47 huge   = 1.0e30;
  48
  49 float
  50 atanf(float x)
  51 {
  52         float w,s1,s2,z;
  53         int32_t ix,hx,id;
  54
  55         GET_FLOAT_WORD(hx,x);
  56         ix = hx&0x7fffffff;
  57         if(ix>=0x4c800000) {    /* if |x| >= 2**26 */
  58             if(ix>0x7f800000)
  59                 return x+x;             /* NaN */
  60             if(hx>0) return  atanhi[3]+*(volatile float *)&atanlo[3];
  61             else     return -atanhi[3]-*(volatile float *)&atanlo[3];
  62         } if (ix < 0x3ee00000) {        /* |x| < 0.4375 */
  63             if (ix < 0x39800000) {      /* |x| < 2**-12 */
  64                 if(huge+x>one) return x;        /* raise inexact */
  65             }
  66             id = -1;
  67         } else {
  68         x = fabsf(x);
  69         if (ix < 0x3f980000) {          /* |x| < 1.1875 */
  70             if (ix < 0x3f300000) {      /* 7/16 <=|x|<11/16 */
  71                 id = 0; x = ((float)2.0*x-one)/((float)2.0+x);
  72             } else {                    /* 11/16<=|x|< 19/16 */
  73                 id = 1; x  = (x-one)/(x+one);
  74             }
  75         } else {
  76             if (ix < 0x401c0000) {      /* |x| < 2.4375 */
  77                 id = 2; x  = (x-(float)1.5)/(one+(float)1.5*x);
  78             } else {                    /* 2.4375 <= |x| < 2**26 */
  79                 id = 3; x  = -(float)1.0/x;
  80             }
  81         }}
  82     /* end of argument reduction */
  83         z = x*x;
  84         w = z*z;
  85     /* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */
  86         s1 = z*(aT[0]+w*(aT[2]+w*aT[4]));
  87         s2 = w*(aT[1]+w*aT[3]);
  88         if (id<0) return x - x*(s1+s2);
  89         else {
  90             z = atanhi[id] - ((x*(s1+s2) - atanlo[id]) - x);
  91             return (hx<0)? -z:z;
  92         }
  93 }