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Re: [Qemu-devel] [PATCH 3/3] Add test suite for json marshalling


From: Anthony Liguori
Subject: Re: [Qemu-devel] [PATCH 3/3] Add test suite for json marshalling
Date: Fri, 13 Nov 2009 08:05:56 -0600
User-agent: Thunderbird 2.0.0.23 (X11/20090825)

Jamie Lokier wrote:
Anthony Liguori wrote:
After checking that we can demarshal, marshal again and compared to
the expected decoded value.  This doesn't work so well for floats
because they cannot be accurately represented in decimal but we try
our best.

Good sprintf/scanf/strtod implementations do guarantee that what's
printed and then parsed gets back the same floating point value, as
long as you have printed sufficient decimal digits.

I'm not sure if FLT_DIG/DLB_DIG are the right number of digits,
though.  Glibc's documentation of those is confusing and they might
mean something a little different.

Eh, I played around quite a bit and the results were disappointing.

$ printf "%f\n" 43.32
43.320000
$ printf "%0.32f\n" 43.32
43.31999999999999999972244424384371

Regards,

Anthony Liguori
-- Jamie







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