/* origin: FreeBSD /usr/src/lib/msun/src/e_expf.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 "libm.h"

static const float half[2] = {0.5, -0.5},
                   ln2hi = 6.9314575195e-1f, /* 0x3f317200 */
    ln2lo = 1.4286067653e-6f,                /* 0x35bfbe8e */
    invln2 = 1.4426950216e+0f,               /* 0x3fb8aa3b */
                                             /*
                                              * Domain [-0.34568, 0.34568], range ~[-4.278e-9, 4.447e-9]:
                                              * |x*(exp(x)+1)/(exp(x)-1) - p(x)| < 2**-27.74
                                              */
    P1 = 1.6666625440e-1f,                   /*  0xaaaa8f.0p-26 */
    P2 = -2.7667332906e-3f;                  /* -0xb55215.0p-32 */

float expf(float x) {
  float_t hi, lo, c, xx, y;
  int k, sign;
  uint32_t hx;

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

  /* special cases */
  if (hx >= 0x42aeac50) {            /* if |x| >= -87.33655f or NaN */
    if (hx >= 0x42b17218 && !sign) { /* x >= 88.722839f */
      /* overflow */
      x *= 0x1p127f;
      return x;
    }
    if (sign) {
      /* underflow */
      FORCE_EVAL(-0x1p-149f / x);
      if (hx >= 0x42cff1b5) /* x <= -103.972084f */
        return 0;
    }
  }

  /* argument reduction */
  if (hx > 0x3eb17218) { /* if |x| > 0.5 ln2 */
    if (hx > 0x3f851592) /* if |x| > 1.5 ln2 */
      k = invln2 * x + half[sign];
    else
      k = 1 - sign - sign;
    hi = x - k * ln2hi; /* k*ln2hi is exact here */
    lo = k * ln2lo;
    x = hi - lo;
  } else if (hx > 0x39000000) { /* |x| > 2**-14 */
    k = 0;
    hi = x;
    lo = 0;
  } else {
    /* raise inexact */
    FORCE_EVAL(0x1p127f + x);
    return 1 + x;
  }

  /* x is now in primary range */
  xx = x * x;
  c = x - xx * (P1 + xx * P2);
  y = 1 + (x * c / (2 - c) - lo + hi);
  if (k == 0)
    return y;
  return scalbnf(y, k);
}