could output several different high digits on most PC Unixen.
float4/.*-qnx=float4-exp-three-digits
float8/.*-bsdi=float8-small-is-zero
float8/.*-freebsd*=float8-small-is-zero
-float8/i386-.*-netbsd=float8-small-is-zero
+float8/i.86-.*-netbsd=float8-small-is-zero
float8/.*-qnx=float8-exp-three-digits
float8/alpha.*-dec-osf=float8-fp-exception
float8/i.86-pc-cygwin*=float8-cygwin