/* e_expf.c -- float version of e_exp.c.
 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
 */

/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice 
 * is preserved.
 * ====================================================
 */

#include <stdint.h>

static const float
one	= 1.0,
halF[2]	= {0.5,-0.5,},
ln2HI[2]   ={ 6.9313812256e-01,		/* 0x3f317180 */
	     -6.9313812256e-01,},	/* 0xbf317180 */
ln2LO[2]   ={ 9.0580006145e-06,  	/* 0x3717f7d1 */
	     -9.0580006145e-06,},	/* 0xb717f7d1 */
invln2 =  1.4426950216e+00, 		/* 0x3fb8aa3b */
P1   =  1.6666667163e-01, /* 0x3e2aaaab */
P2   = -2.7777778450e-03, /* 0xbb360b61 */
P3   =  6.6137559770e-05, /* 0x388ab355 */
P4   = -1.6533901999e-06, /* 0xb5ddea0e */
P5   =  4.1381369442e-08; /* 0x3331bb4c */

typedef union {
  float value;
  uint32_t word;
} _f32;

/* Get a 32 bit int from a float.  */
#define GET_FLOAT_WORD(i,d)                                     \
do {                                                            \
  _f32 gf_u;                                   \
  gf_u.value = (d);                                             \
  (i) = gf_u.word;                                              \
} while (0)

/* Set a float from a 32 bit int.  */
#define SET_FLOAT_WORD(d,i)                                     \
do {                                                            \
  _f32 sf_u;                                   \
  sf_u.word = (i);                                              \
  (d) = sf_u.value;                                             \
} while (0)

float expf(float x)	/* default IEEE double exp */
{
	float y,hi=0,lo=0,c,t;
	int32_t k,xsb;
	uint32_t hx;

	GET_FLOAT_WORD(hx,x);
	xsb = (hx>>31)&1;		/* sign bit of x */
	hx &= 0x7fffffff;		/* high word of |x| */

    /* filter out non-finite argument */
	if(hx >= 0x42b17218) {			/* if |x|>=88.721... */
	    if(hx>0x7f800000)
            return x+x;	 		/* NaN */
        if(hx==0x7f800000)
		    return (xsb==0)? x:0.0f;    /* exp(+-inf)={inf,0} */
	}

    /* argument reduction */
	if(hx > 0x3eb17218) {		/* if  |x| > 0.5 ln2 */ 
	    if(hx < 0x3F851592) {	/* and |x| < 1.5 ln2 */
		    hi = x-ln2HI[xsb]; lo=ln2LO[xsb]; k = 1-xsb-xsb;
	    } else {
		    k  = invln2*x+halF[xsb];
		    t  = k;
		    hi = x - t*ln2HI[0];	/* t*ln2HI is exact here */
		    lo = t*ln2LO[0];
	    }
	    x  = hi - lo;
	} 
	else k = 0;

    /* x is now in primary range */
	t  = x*x;
	c  = x - t*(P1+t*(P2+t*(P3+t*(P4+t*P5))));
	if(k==0) 	return one-((x*c)/(c-(float)2.0)-x); 
	else 		y = one-((lo-(x*c)/((float)2.0-c))-hi);
	{
	    uint32_t hy;
	    GET_FLOAT_WORD(hy,y);
	    SET_FLOAT_WORD(y,hy+(k<<23));	/* add k to y's exponent */
	    return y;
	}
}