source: azure_iot_hub/trunk/musl-1.1.18/src/math/asinl.c@ 388

/* origin: FreeBSD /usr/src/lib/msun/src/e_asinl.c */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunSoft, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */
/*
 * See comments in asin.c.
 * Converted to long double by David Schultz <das@FreeBSD.ORG>.
 */

#include "libm.h"

#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
long double asinl(long double x)
{
        return asin(x);
}
#elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
#include "__invtrigl.h"
#if LDBL_MANT_DIG == 64
#define CLOSETO1(u) (u.i.m>>56 >= 0xf7)
#define CLEARBOTTOM(u) (u.i.m &= -1ULL << 32)
#elif LDBL_MANT_DIG == 113
#define CLOSETO1(u) (u.i.top >= 0xee00)
#define CLEARBOTTOM(u) (u.i.lo = 0)
#endif

long double asinl(long double x)
{
        union ldshape u = {x};
        long double z, r, s;
        uint16_t e = u.i.se & 0x7fff;
        int sign = u.i.se >> 15;

        if (e >= 0x3fff) {   /* |x| >= 1 or nan */
                /* asin(+-1)=+-pi/2 with inexact */
                if (x == 1 || x == -1)
                        return x*pio2_hi + 0x1p-120f;
                return 0/(x-x);
        }
        if (e < 0x3fff - 1) {  /* |x| < 0.5 */
                if (e < 0x3fff - (LDBL_MANT_DIG+1)/2) {
                        /* return x with inexact if x!=0 */
                        FORCE_EVAL(x + 0x1p120f);
                        return x;
                }
                return x + x*__invtrigl_R(x*x);
        }
        /* 1 > |x| >= 0.5 */
        z = (1.0 - fabsl(x))*0.5;
        s = sqrtl(z);
        r = __invtrigl_R(z);
        if (CLOSETO1(u)) {
                x = pio2_hi - (2*(s+s*r)-pio2_lo);
        } else {
                long double f, c;
                u.f = s;
                CLEARBOTTOM(u);
                f = u.f;
                c = (z - f*f)/(s + f);
                x = 0.5*pio2_hi-(2*s*r - (pio2_lo-2*c) - (0.5*pio2_hi-2*f));
        }
        return sign ? -x : x;
}
#endif