3B2 floating point libraries

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1 total messages Started by Ray Brownrigg Wed, 14 Oct 1987 23:03

#619

Author: Ray Brownrigg
Date: Wed, 14 Oct 1987 23:03

19 lines
1424 bytes

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"

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