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00013 #if defined(LIBM_SCCS) && !defined(lint)
00014 static char rcsid[] = "$NetBSD: s_cbrt.c,v 1.8 1995/05/10 20:46:49 jtc Exp $";
00015 #endif
00016
00017 #include "math.h"
00018 #include "mathP.h"
00019
00020
00021
00022
00023 #ifdef __STDC__
00024 static const u_int32_t
00025 #else
00026 static u_int32_t
00027 #endif
00028 B1 = 715094163,
00029 B2 = 696219795;
00030
00031 #ifdef __STDC__
00032 static const double
00033 #else
00034 static double
00035 #endif
00036 C = 5.42857142857142815906e-01,
00037 D = -7.05306122448979611050e-01,
00038 E = 1.41428571428571436819e+00,
00039 F = 1.60714285714285720630e+00,
00040 G = 3.57142857142857150787e-01;
00041
00042 #ifdef __STDC__
00043 double cbrt(double x)
00044 #else
00045 double cbrt(x)
00046 double x;
00047 #endif
00048 {
00049 int32_t hx;
00050 double r,s,t=0.0,w;
00051 u_int32_t sign;
00052 u_int32_t high,low;
00053
00054 GET_HIGH_WORD(hx,x);
00055 sign=hx&0x80000000;
00056 hx ^=sign;
00057 if(hx>=0x7ff00000) return(x+x);
00058 GET_LOW_WORD(low,x);
00059 if((hx|low)==0)
00060 return(x);
00061
00062 SET_HIGH_WORD(x,hx);
00063
00064 if(hx<0x00100000)
00065 {SET_HIGH_WORD(t,0x43500000);
00066 t*=x; GET_HIGH_WORD(high,t); SET_HIGH_WORD(t,high/3+B2);
00067 }
00068 else
00069 SET_HIGH_WORD(t,hx/3+B1);
00070
00071
00072
00073 r=t*t/x;
00074 s=C+r*t;
00075 t*=G+F/(s+E+D/s);
00076
00077
00078 GET_HIGH_WORD(high,t);
00079 INSERT_WORDS(t,high+0x00000001,0);
00080
00081
00082
00083 s=t*t;
00084 r=x/s;
00085 w=t+t;
00086 r=(r-t)/(w+r);
00087 t=t+t*r;
00088
00089
00090 GET_HIGH_WORD(high,t);
00091 SET_HIGH_WORD(t,high|sign);
00092 return(t);
00093 }