/*
 *                               POK header
 *
 * The following file is a part of the POK project. Any modification should
 * made according to the POK licence. You CANNOT use this file or a part of
 * this file is this part of a file for your own project
 *
 * For more information on the POK licence, please see our LICENCE FILE
 *
 * Please follow the coding guidelines described in doc/CODING_GUIDELINES
 *
 *                                      Copyright (c) 2007-2009 POK team
 *
 * Created by julien on Fri Jan 30 14:41:34 2009
 */

/* s_expm1f.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.
 * ====================================================
 */

#ifdef POK_NEEDS_LIBMATH

#include <libm.h>
#include "math_private.h"

static const float huge = 1.0e+30, tiny = 1.0e-30;

static const float one = 1.0, o_threshold = 8.8721679688e+01, /* 0x42b17180 */
    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;

    c = 0;
    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 (hx >= 0x42b17218) { /* if |x|>=88.721... */
            if (hx > 0x7f800000) return x + x; /* NaN */
            if (hx == 0x7f800000) return (xsb == 0) ? x : -1.0; /* exp(+-inf)={inf,-1} */
            if (x > o_threshold) return huge * huge; /* overflow */
        }
        if (xsb != 0) { /* x < -27*ln2, return -1.0 with inexact */
            if (x + tiny < (float)0.0) /* raise inexact */
                return 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) ? (float)0.5 : (float)-0.5);
            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 = (float)0.5 * x;
    hxs = x * hfx;
    r1 = one + hxs * (Q1 + hxs * (Q2 + hxs * (Q3 + hxs * (Q4 + hxs * Q5))));
    t = (float)3.0 - r1 * hfx;
    e = hxs * ((r1 - t) / ((float)6.0 - 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 (float)0.5 * (x - e) - (float)0.5;
        if (k == 1) {
            if (x < (float)-0.25)
                return -(float)2.0 * (e - (x + (float)0.5));
            else
                return one + (float)2.0 * (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 + (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 + (k << 23)); /* add k to y's exponent */
        } else {
            int32_t i;
            SET_FLOAT_WORD(t, ((0x7f - k) << 23)); /* 2^-k */
            y = x - (e + t);
            y += one;
            GET_FLOAT_WORD(i, y);
            SET_FLOAT_WORD(y, i + (k << 23)); /* add k to y's exponent */
        }
    }
    return y;
}

#endif
