/* sf_expm1.c -- float version of s_expm1.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 "fdlibm.h"
#include "math_config.h"

#ifdef __v810__
#define const
#endif

static const float one = 1.0, huge = 1.0e+30, tiny = 1.0e-30,
                   ln2_hi = 6.9313812256e-01, /* 0x3f317180 */
    ln2_lo = 9.0580006145e-06,                /* 0x3717f7d1 */
    invln2 = 1.4426950216e+00,                /* 0x3fb8aa3b */
                                              /* scaled coefficients related to expm1 */
    Q1 = -3.3333335072e-02,                   /* 0xbd088889 */
    Q2 = 1.5873016091e-03,                    /* 0x3ad00d01 */
    Q3 = -7.9365076090e-05,                   /* 0xb8a670cd */
    Q4 = 4.0082177293e-06,                    /* 0x36867e54 */
    Q5 = -2.0109921195e-07;                   /* 0xb457edbb */

float
expm1f(float x)
{
    float      y, hi, lo, c, t, e, hxs, hfx, r1;
    __int32_t  k, xsb;
    __uint32_t hx;

    GET_FLOAT_WORD(hx, x);
    xsb = hx & 0x80000000; /* sign bit of x */
    if (xsb == 0)
        y = x;
    else
        y = -x;       /* y = |x| */
    hx &= 0x7fffffff; /* high word of |x| */

    /* filter out huge and non-finite argument */
    if (hx >= 0x4195b844) { /* if |x|>=27*ln2 */
        if (FLT_UWORD_IS_NAN(hx))
            return x + x;
        if (FLT_UWORD_IS_INFINITE(hx))
            return (xsb == 0) ? x : -1.0f;      /* exp(+-inf)={inf,-1} */
        if (xsb == 0 && hx > FLT_UWORD_LOG_MAX) /* if x>=o_threshold */
            return __math_oflowf(0);            /* overflow */
        if (xsb != 0)                           /* x < -27*ln2, return -1.0 with inexact */
            return __math_inexactf(tiny - one); /* return -1 */
    }

    /* argument reduction */
    if (hx > 0x3eb17218) {     /* if  |x| > 0.5 ln2 */
        if (hx < 0x3F851592) { /* and |x| < 1.5 ln2 */
            if (xsb == 0) {
                hi = x - ln2_hi;
                lo = ln2_lo;
                k = 1;
            } else {
                hi = x + ln2_hi;
                lo = -ln2_lo;
                k = -1;
            }
        } else {
            k = invln2 * x + ((xsb == 0) ? 0.5f : -0.5f);
            t = k;
            hi = x - t * ln2_hi; /* t*ln2_hi is exact here */
            lo = t * ln2_lo;
        }
        x = hi - lo;
        c = (hi - x) - lo;
    } else if (hx < 0x33000000) { /* when |x|<2**-25, return x */
        t = huge + x;             /* return x with inexact flags when x!=0 */
        return x - (t - (huge + x));
    } else
        k = 0;

    /* x is now in primary range */
    hfx = 0.5f * x;
    hxs = x * hfx;
    r1 = one + hxs * (Q1 + hxs * (Q2 + hxs * (Q3 + hxs * (Q4 + hxs * Q5))));
    t = 3.0f - r1 * hfx;
    e = hxs * ((r1 - t) / (6.0f - x * t));
    if (k == 0)
        return x - (x * e - hxs); /* c is 0 */
    else {
        e = (x * (e - c) - c);
        e -= hxs;
        if (k == -1)
            return 0.5f * (x - e) - 0.5f;
        if (k == 1) {
            if (x < -0.25f)
                return -2.0f * (e - (x + 0.5f));
            else
                return one + 2.0f * (x - e);
        }
        if (k <= -2 || k > 56) { /* suffice to return exp(x)-1 */
            __int32_t i;
            y = one - (e - x);
            GET_FLOAT_WORD(i, y);
            SET_FLOAT_WORD(y, i + lsl(k, 23)); /* add k to y's exponent */
            return y - one;
        }
        t = one;
        if (k < 23) {
            __int32_t i;
            SET_FLOAT_WORD(t, 0x3f800000 - (0x1000000 >> k)); /* t=1-2^-k */
            y = t - (e - x);
            GET_FLOAT_WORD(i, y);
            SET_FLOAT_WORD(y, i + lsl(k, 23)); /* add k to y's exponent */
        } else {
            __int32_t i;
            SET_FLOAT_WORD(t, lsl((0x7f - k), 23)); /* 2^-k */
            y = x - (e + t);
            y += one;
            GET_FLOAT_WORD(i, y);
            SET_FLOAT_WORD(y, i + lsl(k, 23)); /* add k to y's exponent */
        }
    }
    return y;
}

_MATH_ALIAS_f_f(expm1)
