Architecture floating-point underflow information wanted

[Joseph S. Myers]

As part of fixing bug 14047, I'd like information about how each glibc 
architecture (libc and ports) detects floating-point underflow.  (IEEE 
754-2008 gives two options: "before rounding" (exponent would be below 
normal range if both exponent range and mantissa precision were unbounded) 
and "after rounding" (exponent of the rounded value would be below normal 
range if the exponent range were unbounded and values with all exponents 
had the same mantissa precision as for normal values).)

You can identify the choice made by an architecture by running the 
following program.  The GCC and glibc versions used to build and run the 
program don't matter, but it's best to run this on hardware not an 
emulator since it's quite possible some emulators could get this sort of 
detail wrong.  It may also be possible to find this information in 
architecture manuals.

#include <fenv.h>
#include <stdio.h>

volatile float a = 0x1.fffp-126;
volatile float b = 0x1.0008p-1;
volatile float c;

int
main (void)
{
  feclearexcept (FE_ALL_EXCEPT);
  c = a * b;
  if (fetestexcept (FE_UNDERFLOW))
    puts ("before rounding");
  else
    puts ("after rounding");
  return 0;
}

I'm looking for information for the following architectures:

s390-32, s390-64
alpha
am33
hppa
ia64
m68k (classic)

I have the following information for architectures I have access to:

x86, x86_64: after rounding
powerpc32, powerpc64: before rounding
sh: after rounding
sparc32, sparc64: before rounding
arm: before rounding
m68k (coldfire): before rounding
mips32, mips64: after rounding

(Tile does not support the underflow exception so the question is 
inapplicable there; I propose to use "before rounding" as a default for 
such architectures for strto*.)

-- 
Joseph S. Myers
joseph@codesourcery.com