Re: [Qemu-devel] [PATCH 4/7] qapi: String visitor, use %f represenation for floats

[Michael Roth <mdroth@linux.vnet.ibm.com>]

On Fri, May 11, 2012 at 01:34:01PM -0300, Luiz Capitulino wrote:
> On Fri, 27 Apr 2012 15:21:20 -0500
> Michael Roth <mdroth@linux.vnet.ibm.com> wrote:
> 
> > Currently string-output-visitor formats floats as %g, which is nice in
> > that trailing 0's are automatically truncated, but otherwise this causes
> > some issues:
> > 
> >  - it 6 uses significant figures instead of 6 decimal places, which
> >    means something like 155777.5 (which even has an exact floating point
> >    representation) will be rounded to 155778 when converted to a string.
> > 
> >  - output will be presented in scientific notation when the normalized
> >    form requires a 10^x multiplier. Not a huge deal, but arguably less
> >    readable for command-line arguments.
> > 
> >  - due to using sig figs instead of hard-defined decimal places, it
> >    fails a lot of the test-visitor-serialization unit tests for floats.
> > 
> > Instead, let's just use %f, which is what the QJSON and the QMP visitors
> > use.
> > 
> > Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
> > ---
> >  qapi/string-output-visitor.c       |    2 +-
> >  tests/test-string-output-visitor.c |    2 +-
> >  2 files changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/qapi/string-output-visitor.c b/qapi/string-output-visitor.c
> > index 92b0305..34e525e 100644
> > --- a/qapi/string-output-visitor.c
> > +++ b/qapi/string-output-visitor.c
> > @@ -52,7 +52,7 @@ static void print_type_number(Visitor *v, double *obj, const char *name,
> >                                Error **errp)
> >  {
> >      StringOutputVisitor *sov = DO_UPCAST(StringOutputVisitor, visitor, v);
> > -    string_output_set(sov, g_strdup_printf("%g", *obj));
> > +    string_output_set(sov, g_strdup_printf("%f", *obj));
> 
> Doesn't look like a bug fix worth it for 1.1, am I wrong?

Well, object_property_print() is the only string-output-visitor user,
and it's not currently used. I don't see this changing for 1.1, so this
can probably wait.

> 
> >  }
> >  
> >  char *string_output_get_string(StringOutputVisitor *sov)
> > diff --git a/tests/test-string-output-visitor.c b/tests/test-string-output-visitor.c
> > index 22909b8..608f14a 100644
> > --- a/tests/test-string-output-visitor.c
> > +++ b/tests/test-string-output-visitor.c
> > @@ -84,7 +84,7 @@ static void test_visitor_out_number(TestOutputVisitorData *data,
> >  
> >      str = string_output_get_string(data->sov);
> >      g_assert(str != NULL);
> > -    g_assert_cmpstr(str, ==, "3.14");
> > +    g_assert_cmpstr(str, ==, "3.140000");
> >      g_free(str);
> >  }
> >  
>