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/* e_expf.c -- float version of e_exp.c.
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 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
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 */
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/*
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 * ====================================================
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 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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 *
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 * Developed at SunPro, a Sun Microsystems, Inc. business.
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 * Permission to use, copy, modify, and distribute this
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 * software is freely granted, provided that this notice
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 * is preserved.
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 * ====================================================
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 */
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#ifndef lint
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static char rcsid[] = "$\Id: e_expf.c,v 1.3 1996/07/12 18:57:56 jkh Exp $";
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#endif
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#include "math.h"
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#include "math_private.h"
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#ifdef __STDC__
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static const float
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#else
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static float
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#endif
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one     = 1.0,
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halF[2] = {0.5,-0.5,},
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huge    = 1.0e+30,
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twom100 = 7.8886090522e-31,      /* 2**-100=0x0d800000 */
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o_threshold=  8.8721679688e+01,  /* 0x42b17180 */
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u_threshold= -1.0397208405e+02,  /* 0xc2cff1b5 */
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ln2HI[2]   ={ 6.9313812256e-01,         /* 0x3f317180 */
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             -6.9313812256e-01,},       /* 0xbf317180 */
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ln2LO[2]   ={ 9.0580006145e-06,         /* 0x3717f7d1 */
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             -9.0580006145e-06,},       /* 0xb717f7d1 */
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invln2 =  1.4426950216e+00,             /* 0x3fb8aa3b */
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P1   =  1.6666667163e-01, /* 0x3e2aaaab */
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P2   = -2.7777778450e-03, /* 0xbb360b61 */
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P3   =  6.6137559770e-05, /* 0x388ab355 */
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P4   = -1.6533901999e-06, /* 0xb5ddea0e */
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P5   =  4.1381369442e-08; /* 0x3331bb4c */
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#ifdef __STDC__
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        float __ieee754_expf(float x)   /* default IEEE double exp */
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#else
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        float __ieee754_expf(x) /* default IEEE double exp */
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        float x;
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#endif
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{
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        float y,hi=0.0,lo=0.0,c,t;
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        int32_t k=0,xsb;
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        u_int32_t hx;
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        GET_FLOAT_WORD(hx,x);
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        xsb = (hx>>31)&1;               /* sign bit of x */
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        hx &= 0x7fffffff;               /* high word of |x| */
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    /* filter out non-finite argument */
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        if(hx >= 0x42b17218) {                  /* if |x|>=88.721... */
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            if(hx>0x7f800000)
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                 return x+x;                    /* NaN */
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            if(hx==0x7f800000)
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                return (xsb==0)? x:0.0;         /* exp(+-inf)={inf,0} */
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            if(x > o_threshold) return huge*huge; /* overflow */
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            if(x < u_threshold) return twom100*twom100; /* underflow */
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        }
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    /* argument reduction */
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        if(hx > 0x3eb17218) {           /* if  |x| > 0.5 ln2 */
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            if(hx < 0x3F851592) {       /* and |x| < 1.5 ln2 */
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                hi = x-ln2HI[xsb]; lo=ln2LO[xsb]; k = 1-xsb-xsb;
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            } else {
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                k  = invln2*x+halF[xsb];
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                t  = k;
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                hi = x - t*ln2HI[0];    /* t*ln2HI is exact here */
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                lo = t*ln2LO[0];
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            }
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            x  = hi - lo;
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        }
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        else if(hx < 0x31800000)  {     /* when |x|<2**-28 */
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            if(huge+x>one) return one+x;/* trigger inexact */
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        }
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        else k = 0;
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    /* x is now in primary range */
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        t  = x*x;
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        c  = x - t*(P1+t*(P2+t*(P3+t*(P4+t*P5))));
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        if(k==0)        return one-((x*c)/(c-(float)2.0)-x);
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        else            y = one-((lo-(x*c)/((float)2.0-c))-hi);
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        if(k >= -125) {
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            u_int32_t hy;
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            GET_FLOAT_WORD(hy,y);
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            SET_FLOAT_WORD(y,hy+(k<<23));       /* add k to y's exponent */
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            return y;
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        } else {
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            u_int32_t hy;
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            GET_FLOAT_WORD(hy,y);
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            SET_FLOAT_WORD(y,hy+((k+100)<<23)); /* add k to y's exponent */
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            return y*twom100;
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        }
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}