sysdeps/ieee754/flt-32/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 #if defined(LIBM_SCCS) && !defined(lint)
  17 static char rcsid[] = "$NetBSD: s_atanf.c,v 1.4 1995/05/10 20:46:47 jtc Exp $";
  18 #endif
  19
  20 #include "math.h"
  21 #include "math_private.h"
  22
  23 #ifdef __STDC__
  24 static const float atanhi[] = {
  25 #else
  26 static float atanhi[] = {
  27 #endif
  28   4.6364760399e-01, /* atan(0.5)hi 0x3eed6338 */
  29   7.8539812565e-01, /* atan(1.0)hi 0x3f490fda */
  30   9.8279368877e-01, /* atan(1.5)hi 0x3f7b985e */
  31   1.5707962513e+00, /* atan(inf)hi 0x3fc90fda */
  32 };
  33
  34 #ifdef __STDC__
  35 static const float atanlo[] = {
  36 #else
  37 static float atanlo[] = {
  38 #endif
  39   5.0121582440e-09, /* atan(0.5)lo 0x31ac3769 */
  40   3.7748947079e-08, /* atan(1.0)lo 0x33222168 */
  41   3.4473217170e-08, /* atan(1.5)lo 0x33140fb4 */
  42   7.5497894159e-08, /* atan(inf)lo 0x33a22168 */
  43 };
  44
  45 #ifdef __STDC__
  46 static const float aT[] = {
  47 #else
  48 static float aT[] = {
  49 #endif
  50   3.3333334327e-01, /* 0x3eaaaaaa */
  51  -2.0000000298e-01, /* 0xbe4ccccd */
  52   1.4285714924e-01, /* 0x3e124925 */
  53  -1.1111110449e-01, /* 0xbde38e38 */
  54   9.0908870101e-02, /* 0x3dba2e6e */
  55  -7.6918758452e-02, /* 0xbd9d8795 */
  56   6.6610731184e-02, /* 0x3d886b35 */
  57  -5.8335702866e-02, /* 0xbd6ef16b */
  58   4.9768779427e-02, /* 0x3d4bda59 */
  59  -3.6531571299e-02, /* 0xbd15a221 */
  60   1.6285819933e-02, /* 0x3c8569d7 */
  61 };
  62
  63 #ifdef __STDC__
  64         static const float
  65 #else
  66         static float
  67 #endif
  68 one   = 1.0,
  69 huge   = 1.0e30;
  70
  71 #ifdef __STDC__
  72         float __atanf(float x)
  73 #else
  74         float __atanf(x)
  75         float x;
  76 #endif
  77 {
  78         float w,s1,s2,z;
  79         int32_t ix,hx,id;
  80
  81         GET_FLOAT_WORD(hx,x);
  82         ix = hx&0x7fffffff;
  83         if(ix>=0x50800000) {    /* if |x| >= 2^34 */
  84             if(ix>0x7f800000)
  85                 return x+x;             /* NaN */
  86             if(hx>0) return  atanhi[3]+atanlo[3];
  87             else     return -atanhi[3]-atanlo[3];
  88         } if (ix < 0x3ee00000) {        /* |x| < 0.4375 */
  89             if (ix < 0x31000000) {      /* |x| < 2^-29 */
  90                 if(huge+x>one) return x;        /* raise inexact */
  91             }
  92             id = -1;
  93         } else {
  94         x = fabsf(x);
  95         if (ix < 0x3f980000) {          /* |x| < 1.1875 */
  96             if (ix < 0x3f300000) {      /* 7/16 <=|x|<11/16 */
  97                 id = 0; x = ((float)2.0*x-one)/((float)2.0+x);
  98             } else {                    /* 11/16<=|x|< 19/16 */
  99                 id = 1; x  = (x-one)/(x+one);
 100             }
 101         } else {
 102             if (ix < 0x401c0000) {      /* |x| < 2.4375 */
 103                 id = 2; x  = (x-(float)1.5)/(one+(float)1.5*x);
 104             } else {                    /* 2.4375 <= |x| < 2^66 */
 105                 id = 3; x  = -(float)1.0/x;
 106             }
 107         }}
 108     /* end of argument reduction */
 109         z = x*x;
 110         w = z*z;
 111     /* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */
 112         s1 = z*(aT[0]+w*(aT[2]+w*(aT[4]+w*(aT[6]+w*(aT[8]+w*aT[10])))));
 113         s2 = w*(aT[1]+w*(aT[3]+w*(aT[5]+w*(aT[7]+w*aT[9]))));
 114         if (id<0) return x - x*(s1+s2);
 115         else {
 116             z = atanhi[id] - ((x*(s1+s2) - atanlo[id]) - x);
 117             return (hx<0)? -z:z;
 118         }
 119 }
 120 weak_alias (__atanf, atanf)