underflow handled much more slowly in gcc than in icc

Issue

• Underflow in gcc is handled much more slowly in gcc than icc.
• The solution is probably to take some ideas from projects like http://lipforge.ens-lyon.fr/www/crlibm/ and incorporate them into glibc.
• Currently glibc's libm is derived from IBM Ultimate Precision Math Library which preserves the precision perfectly but does so at an immense cost in certain circumstances.