Package: clisp
Version: 1:2.41-1
Severity: normal
Hi,
I'm trying to compare a floating-point number and a rational.
According to the rule of float and rational contagion, described in
CLHS 12.1.4.1, and X3J13 issue
CONTAGION-ON-NUMERICAL-COMPARISONS:TRANSITIVE, such a comparison
should always return the mathematically correct result, as if the
floating-point number were first converted to a rational with
RATIONAL. Instead, CLISP signals an underflow condition:
$ clisp -q -x '( (expt 10 -100) least-positive-short-float)'
*** - floating point underflow
The Implementation Notes for GNU CLISP, sections 12.2.3.1 and
12.2.3.2, don't seem to say anything about comparisons, but mention
two variables which control ANSI-compliance. CLISP behaves the same
when invoked with -ansi, to set these and any similar variables to
T.
$ clisp -ansi -q -x '( (expt 10 -100) least-positive-short-float)'
*** - floating point underflow
This X3J13 issue is listed as supported in the Implementation Notes for GNU
CLISP:
http://clisp.cons.org/impnotes.html#issues
CLISP behaves as expected if the floating-point number is filtered
through RATIONAL. (Note that CLHS 12.1.4.1 explicitly states When
rationals and floats are compared by a numerical function, the
function rational is effectively called to convert the float to a
rational and then an exact comparison is performed.)
$ clisp -q -x '( (expt 10 -100) (rational least-positive-short-float))'
T
$ clisp -q -x '( (expt 10 -10) (rational least-positive-short-float))'
NIL
I'm fairly certain CLISP is in error.
Thanks,
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ii libc6 2.3.6.ds1-13 GNU C Library: Shared libraries
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ii libsm6 1:1.0.1-3X11 Session Management library
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J.P. Larocque: [EMAIL PROTECTED], [EMAIL PROTECTED]
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