math.c, acosh.h, domain_check, MS Windows - possible bug

Hi,

Ruby 1.8.5 p12
Windows XP Pro SP 2 and Solaris 10

I noticed that, based on the Changelog, the domain_check() helper
function was added to math.c to see if isnan() returns true and, if it
does, an Errno::ERANGE or Errno::EDOM error is raised. Otherwise, a
method will return "Infinity". But, there seems to be a discrepancy
between UNIX and MS Windows.

For example:

irb(main):001:0> RUBY_PLATFORM
=> "i386-mswin32_80"

irb(main):002:0> Math.atanh(1)
=> Infinity # ???

irb(main):003:0> Math.atanh(1.01)
Errno::EDOM: Domain error - atanh

irb(main):001:0> RUBY_PLATFORM
=> "sparc-solaris2.10"

irb(main):002:0> Math.atanh(1)
Errno::ERANGE: Result too large - atanh

irb(main):003:0> Math.atanh(1.01)
Errno::EDOM: Argument out of domain - atanh

If this is a bug, then what about the following patch?

--- acosh.orig  Sat Oct 18 08:04:18 2003
+++ acosh.c     Fri Feb 02 13:25:11 2007
@@ -81,7 +81,7 @@
     double z = fabs(x);

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

That will force an Errno::EDOM error if x is 1 or -1 at least.

Or is this a bug in MS Windows? I ask because the following does *not*
set errno:

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

double atanh(double);

int main(){
   double x = atanh(1);

   if(errno)
      printf("ERROR: %i\n", errno);
   else
      printf("NO ERROR\n");

   printf("ATANH: %e\n", x);

   return 0;
}

double atanh(double x){
   return log((1 + x) / (1 - x)) / 2;
}

This prints out:

NO ERROR
ATANH: 1.#INF00e+000

Regards,

Dan


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