ray@dsiramd.nz (Ray Brownrigg) (10/15/87)
I have uncovered a strange bug in the floating point routines for the
Fortran XLA+ and C-FP+ compilers for an AT&T 3B2 (with MAU), relating
to non-integral powers of 0.5 (and perhaps other numbers as well). For
example the expression 0.5**Y returns the value 0.5**(Y-1) when Y is
2.5, 4.5, 6.5, 8.5, ... Further, using C-FP+, the statement
printf("%10.8f\n", pow(0.5, 2.5))
results in a zero being output.
I have reported the bugs (to Olivetti), but would be interested if anybody
else has seen the same problem.
Otherwise, beware. One workaround it to use exp(0.5*log(y)), but this is
not easy in a package as large as the S statistical package.
--
Ray Brownrigg UUCP: {utai!calgary,uunet}!vuwcomp!dsiramd!ray
Applied Maths Div, DSIR ACSnet: ray@dsiramd.nz[@munnari]
PO Box 1335 System: OLIVETTI/AT&T 3B2/400B+, System V R3.0
Wellington, New Zealand "UNX -rules -OK"