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From: Paul Giaccone (paulg_at_[hidden])
Date: 2006-03-14 12:38:48

I'm having problems with deserialising floating-point (double) values
that are written to an XML file. I'm reading the values back in and
comparing them to what I saved to ensure that my file has been written
correctly. However, some of the values differ in about the seventeenth
significant figure (or thereabouts).

I thought Boost serialization used some numerical limit to make sure
that values are serialised exactly to full precision, so what is
happening here?

Value in original object, written to file: 0.0019075645054089487
Value actually stored in file (by examination of XML file):
0.0019075645054089487 [identical to value written to file]
Value after deserialisation: 0.0019075645054089489

It looks like there is a difference in the least-significant bit, as
examining the memory for these two values gives:

Original value: b4 83 9b ca e7 40 5f 3f
Deserialised value: b5 83 9b ca e7 40 5f 3f

(where the least-significant byte is on the left)

Note the difference in the first bytes.

I'm using Boost 1.33.1 with Visual Studio 7.1.3088 in debug mode.


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