ruby/missing/acosh.c

/**********************************************************************

  acosh.c -

  $Author$
  $Date$
  created at: Fri Apr 12 00:34:17 JST 2002

  public domain rewrite of acosh(3), asinh(3) and atanh(3)

**********************************************************************/

#include <errno.h>
#include <float.h>
#include <math.h>

/* DBL_MANT_DIG must be less than 4 times of bits of int */
#ifndef DBL_MANT_DIG
#define DBL_MANT_DIG 53		/* in this case, at least 12 digit precision */
#endif
#define BIG_CRITERIA_BIT (1<<DBL_MANT_DIG/2)
#if BIG_CRITERIA_BIT > 0
#define BIG_CRITERIA (1.0*BIG_CRITERIA_BIT)
#else
#define BIG_CRITERIA (1.0*(1<<DBL_MANT_DIG/4)*(1<<(DBL_MANT_DIG/2+1-DBL_MANT_DIG/4)))
#endif
#define SMALL_CRITERIA_BIT (1<<(DBL_MANT_DIG/3))
#if SMALL_CRITERIA_BIT > 0
#define SMALL_CRITERIA (1.0/SMALL_CRITERIA_BIT)
#else
#define SMALL_CRITERIA (1.0*(1<<DBL_MANT_DIG/4)*(1<<(DBL_MANT_DIG/3+1-DBL_MANT_DIG/4)))
#endif

#ifndef HAVE_ACOSH
double
acosh(double x)
{
    if (x < 1)
	x = -1;			/* NaN */
    else if (x == 1)
	return 0;
    else if (x > BIG_CRITERIA)
	x += x;
    else
	x += sqrt((x + 1) * (x - 1));
    return log(x);
}
#endif

#ifndef HAVE_ASINH
double
asinh(double x)
{
    int neg = x < 0;
    double z = fabs(x);

    if (z < SMALL_CRITERIA) return x;
    if (z < (1.0/(1<<DBL_MANT_DIG/5))) {
	double x2 = z * z;
	z *= 1 + x2 * (-1.0/6.0 + x2 * 3.0/40.0);
    }
    else if (z > BIG_CRITERIA) {
	z = log(z + z);
    }
    else {
	z = log(z + sqrt(z * z + 1));
    }
    if (neg) z = -z;
    return z;
}
#endif

#ifndef HAVE_ATANH
double
atanh(double x)
{
    int neg = x < 0;
    double z = fabs(x);

    if (z < SMALL_CRITERIA) return x;
    z = log(z > 1 ? -1 : (1 + z) / (1 - z)) / 2;
    if (neg) z = -z;
    return z;
}
#endif