Date: Tue, 10 Apr 2012 10:34:28 -0600 From: Ian Lepore <freebsd@damnhippie.dyndns.org> To: freebsd-arm@freebsd.org Subject: Re: Trouble with long double support on arm Message-ID: <1334075668.1082.93.camel@revolution.hippie.lan> In-Reply-To: <1334002103.1082.84.camel@revolution.hippie.lan> References: <1334002103.1082.84.camel@revolution.hippie.lan>
next in thread | previous in thread | raw e-mail | index | archive | help
On Mon, 2012-04-09 at 14:08 -0600, Ian Lepore wrote:
> A collegue at work has just run into trouble with printf() and long
> double with softfloat on arm. It looks like C++ stream output has the
> same problem. It appears that the math itself works correctly, but
> attempting to print the value gives wrong output.
>
> We're pretty sure that this is a problem only with coverting long double
> values to ascii. In all other ways, long double seems to be properly
> handled the same as double (which you'd expect given the defines in
> float.h for arm). We use long double types in a few places in our
> products where wrong results would lead to in-your-face wrong behavior,
> and we've never seen anything like that. This was noticed in some debug
> logging which is normally disabled but he happened to be looking at it
> closely today.
>
> This simple program:
>
> #include <float.h>
> #include <stdio.h>
> #include <iostream>
>
> int main(int argc, char **argv)
> {
> printf("Long Double Test\n");
> printf("sizeof(double): %d\n", sizeof(double));
> printf("sizeof(long double): %d\n", sizeof(long double));
>
> double f = 9999999.898991832509637;
> long double lf = f;
>
> printf("double as double: %f\n", f);
> printf("long double as double: %f\n", lf);
> printf("double as long double: %Lf\n", f);
> printf("long double as long double: %Lf\n", lf);
> std::cout << "long double via cout " << lf << std::endl;
> printf("double as hex double: %A\n", f);
> printf("long double as hex long double: %LA\n", lf);
>
> return 0;
> }
>
> Produces this output:
>
> # /usr/tsc/bin/testsimple
> Long Double Test
> sizeof(double): 8
> sizeof(long double): 8
> double as double: 9999999.898992
> long double as double: 9999999.898992
> double as long double: 1611391.898991
> long double as long double: 1611391.898991
> long double via cout 1.61139e+06
> double as hex double: 0X1.312CFFCC48A85P+23
> long double as hex long double: 0X1.312CFFCC48A85P+23
>
> I get the same output on 8.2 and 9.0. You'd expect the "double as long
> double" case to be wrong, but it seems like it might be a clue that the
> "long double as long double" case is the same value.
>
> I pointed him at the twisty maze of lib/libc, lib/msun, and contrib/gcc,
> and he's currently trying to track down which function actually gets
> called to handle %Lf, but I figured I'd ask here as well in case
> somebody has already fought this battle and knows what's going on.
>
> -- Ian
A followup to help anyone who stumbles across this thread in the
future...
This problem was identified a couple months ago by Maks Verver, and the
fix was commited in r230188.
-- Ian
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?1334075668.1082.93.camel>