On 11/25/08, Roland Mainz <[EMAIL PROTECTED]> wrote:
> Roland Mainz wrote:
> >
> > Hi!
> >
> > ----
> >
> > Is there a reason why ksh93 does not display the negative sign for the
> > value zero ? For example if I have use the C99 function "copysign"
> > (copies absolute value of operant a and sign of operant b) I get this
> > for { a=5, b=-0 }:
> > -- snip --
> > $ ksh93 -c 'float x; (( x=copysign(5, -0) )) ; printf "%f\n"
> > x'
> > -5.000000
> > -- snip --
> >
> > Now if I swap operands a and b I get this result:
> > -- snip --
> > $ ksh93 -c 'float x; (( x=copysign(0, -5) )) ; printf "%f\n"
> > x'
> > 0.000000
> > -- snip --
> >
> > AFAIK this result should be "-0.000000" ... or not ?
> >
> > BTW: Parsing of "-0" doesn't seem to work either, e.g.
> > -- snip --
> > $ ksh93 -c 'float x a=-1 b=-0; (( x=copysign(a, b) )) ; printf "%f\n"
> > x'
>
>
> There is a small mistake: -0 is an integer value - it should be "-0." in
> this case, e.g. the line should be:
> -- snip --
> $ ksh93 -c 'float x a=-1.0 b=-0.0; (( x=copysign(a, b) )) ; printf
> "%f\n" x'
> -- snip --
>
>
> > 1.000000
> > -- snip --
> > ... while AFAIK it should be "-1.000000" since the 2nd operand of
> > "copysign" defines the sign of the result.
>
>
> BTW: As someone else pointed out the C99 spec for "copysign" allows some
> "leeway", however my primary concern was that the shell does not seem
> parse "-0.0" correctly and that $ printf "%a\n" x # does not return the
> sign of zero.
>
> For comparisation the following testcase...
> -- snip --
> #include <stdlib.h>
> #include <stdio.h>
> #include <math.h>
>
> #define SD(x) strtod(#x, NULL)
>
> int main(int ac, char *av[])
> {
> double a, b, result;
>
> a=SD(5.), b=SD(-0.);
> result=copysign(a, b);
> printf("a=%f, b=%f, result1=%f, %a\n", a, b, result, result);
>
> a=SD(-0.), b=SD(5.);
> result=copysign(a, b);
> printf("a=%f, b=%f, result1=%f, %a\n", a, b, result, result);
>
> a=SD(-0.), b=SD(-5.);
> result=copysign(a, b);
> printf("a=%f, b=%f, result1=%f, %a\n", a, b, result, result);
>
> return EXIT_SUCCESS;
> }
> -- snip --
> ... returns on Solaris 11/SPARC:
> -- snip --
> $ rm -f a.out ; cc -xc99=%all -lm
> zerosign.c
> $
> ./a.out
> a=5.000000, b=-0.000000, result1=-5.000000, -0x1.4000000000000p+2
> a=-0.000000, b=5.000000, result1=0.000000, 0x0.0000000000000p+0
> a=-0.000000, b=-5.000000, result1=-0.000000, -0x0.0000000000000p+0
> -- snip --
> ... and on SuSE Linux 10.0:
> -- snip --
> ./a.out
> a=5.000000, b=-0.000000, result1=-5.000000, -0x1.4p+2
> a=-0.000000, b=5.000000, result1=0.000000, 0x0p+0
> a=-0.000000, b=-5.000000, result1=-0.000000, -0x0p+0
> -- snip --
>
> Somehow it looks only the shell looses the sign of a negative zero value
> in this case.
I think I've seen code in print.c which tests for 0. and not iszero()
as required. This is unfortunately only half the bug since the parser
misreads typeset -E x=-0.0 as x=0.0.
Irek
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