Date: Mon, 2 Nov 92 22:22:36 EST
From: ronis AT ronis DOT chem DOT mcgill DOT ca (David Ronis)
To: djgpp AT sun DOT soe DOT clarkson DOT edu
Subject: Problem with tanh in version 1.09

Hi DJ,

I'm in the process of bringing over and unpacking version 1.09 of
djgpp.  While doing this, I decided to have a look at some of the
sources that were changed, and in particular, at those I've looked at
in the past.  One of the first ones I examined is incorrect; specifically,
libsr/m/src/tanh.c.

Your code reads:

#include <math.h>

double tanh(double x)
{
  const double ebig = exp(fabs(x));
  const double esmall = 1.0/ebig;
  return (ebig - esmall) / (ebig + esmall);
}

This makes tanh(x) an even function of x.  It should be odd.  The problem
can be removed by getting rid of the fabs(x), or you can do something
like you've done in the sinh function; e.g.,

#include <math.h>

double tanh(double x)
{

  if(x>=0.0){ 
    const double epos=exp(x); 
    return (epos-1.0/epos)/2.0; 
  }
  else { 
    const double eneg=exp(-x); 
    return (1.0/eneg-eneg)/2.0; 
  }
}


In addition, I noticed that in asinh.c you do a test x>0, where x is a
double.  This is probably picky, but shouldn't it be x>0.0? Does it
matter?

David Ronis