[Python-bugs-list] [ python-Bugs-659709 ] bogus computation of float length

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Bugs item #659709, was opened at 2002-12-29 17:19
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Category: None
Group: None
>Status: Closed
>Resolution: Fixed
Priority: 5
Submitted By: Martin v. Löwis (loewis)
Assigned to: M.-A. Lemburg (lemburg)
Summary: bogus computation of float length

Initial Comment:
The computation introduced in rev 2.70 of 
stringobject.c:formatfloat is bogus. If the expression

"%.86f" %  
999999999999999963589629496524800.00001

is computed, then the test whether this is smaller than 
1e50 will succeed, so it continues to be printed as a 
float. However, the result has 33 digits before the 
decimal point, and 86 digits after the decimal point, so 
the entire result will need 121 bytes, more than the 120 
bytes of buffer available.

See Debian bug 172531 for how this crashes Python 
2.1; for Python 2.2, it won't crash as the snprintf 
protects the buffer. However, the result is still incorrect:  
since the buffer is to small to represent 86 digits after 
the decimal point, an exception should be raised.

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>Comment By: M.-A. Lemburg (lemburg)
Date: 2002-12-29 20:44

Message:
Logged In: YES 
user_id=38388

Fix checked in.

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