compiler/stdc/math/e_atan2f.c

   1 /* e_atan2f.c -- float version of e_atan2.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/e_atan2f.c,v 1.12 2008/08/03 17:39:54 das Exp $";
  18 #endif
  19
  20 #include "math.h"
  21 #include "math_private.h"
  22
  23 static const volatile float
  24 tiny __attribute__ ((__section__(".rodata,\"a\" " SECTIONCOMMENT))) = 1.0e-30;
  25 static const float
  26 zero  = 0.0,
  27 pi_o_4  = 7.8539818525e-01, /* 0x3f490fdb */
  28 pi_o_2  = 1.5707963705e+00, /* 0x3fc90fdb */
  29 pi      = 3.1415927410e+00; /* 0x40490fdb */
  30 static const volatile float
  31 pi_lo __attribute__ ((__section__(".rodata,\"a\" " SECTIONCOMMENT))) = -8.7422776573e-08; /* 0xb3bbbd2e */
  32
  33 float
  34 __ieee754_atan2f(float y, float x)
  35 {
  36         float z;
  37         int32_t k,m,hx,hy,ix,iy;
  38
  39         GET_FLOAT_WORD(hx,x);
  40         ix = hx&0x7fffffff;
  41         GET_FLOAT_WORD(hy,y);
  42         iy = hy&0x7fffffff;
  43         if((ix>0x7f800000)||
  44            (iy>0x7f800000))     /* x or y is NaN */
  45            return x+y;
  46         if(hx==0x3f800000) return atanf(y);   /* x=1.0 */
  47         m = ((hy>>31)&1)|((hx>>30)&2);  /* 2*sign(x)+sign(y) */
  48
  49     /* when y = 0 */
  50         if(iy==0) {
  51             switch(m) {
  52                 case 0:
  53                 case 1: return y;       /* atan(+-0,+anything)=+-0 */
  54                 case 2: return  pi+tiny;/* atan(+0,-anything) = pi */
  55                 case 3: return -pi-tiny;/* atan(-0,-anything) =-pi */
  56             }
  57         }
  58     /* when x = 0 */
  59         if(ix==0) return (hy<0)?  -pi_o_2-tiny: pi_o_2+tiny;
  60
  61     /* when x is INF */
  62         if(ix==0x7f800000) {
  63             if(iy==0x7f800000) {
  64                 switch(m) {
  65                     case 0: return  pi_o_4+tiny;/* atan(+INF,+INF) */
  66                     case 1: return -pi_o_4-tiny;/* atan(-INF,+INF) */
  67                     case 2: return  (float)3.0*pi_o_4+tiny;/*atan(+INF,-INF)*/
  68                     case 3: return (float)-3.0*pi_o_4-tiny;/*atan(-INF,-INF)*/
  69                 }
  70             } else {
  71                 switch(m) {
  72                     case 0: return  zero  ;     /* atan(+...,+INF) */
  73                     case 1: return -zero  ;     /* atan(-...,+INF) */
  74                     case 2: return  pi+tiny  ;  /* atan(+...,-INF) */
  75                     case 3: return -pi-tiny  ;  /* atan(-...,-INF) */
  76                 }
  77             }
  78         }
  79     /* when y is INF */
  80         if(iy==0x7f800000) return (hy<0)? -pi_o_2-tiny: pi_o_2+tiny;
  81
  82     /* compute y/x */
  83         k = (iy-ix)>>23;
  84         if(k > 26) {                    /* |y/x| >  2**26 */
  85             z=pi_o_2+(float)0.5*pi_lo;
  86             m&=1;
  87         }
  88         else if(k<-26&&hx<0) z=0.0;     /* 0 > |y|/x > -2**-26 */
  89         else z=atanf(fabsf(y/x));       /* safe to do y/x */
  90         switch (m) {
  91             case 0: return       z  ;   /* atan(+,+) */
  92             case 1: return      -z  ;   /* atan(-,+) */
  93             case 2: return  pi-(z-pi_lo);/* atan(+,-) */
  94             default: /* case 3 */
  95                     return  (z-pi_lo)-pi;/* atan(-,-) */
  96         }
  97 }