[Tcl-bugs] [ tcl-Bugs-1770224 ] TclGetNumberFromObj caller must save result

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Bugs item #1770224, was opened at 2007-08-08 14:57
Message generated for change (Comment added) made by dgp
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Category: 46. Bytecode Compiler
Group: development: 8.5a7
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Don Porter (dgp)
Assigned to: Don Porter (dgp)
Summary: TclGetNumberFromObj caller must save result

Initial Comment:

For example:

% >> -0x8000000000000001 0x8000000000000000
0

Result should be -1.  [>> $big $wide] is ok:

% >> -0x8000000000000001 0x7fffffffffffffff
-1

And clearly, shifting that -1 one more bit
ought to return -1 again, not 0.

Perhaps a clue... it's not always broken:

% >> -0x8000000000000000 0x8000000000000000
-1


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>Comment By: Don Porter (dgp)
Date: 2007-08-08 16:21

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Ok, problem did not show up elsewhere.
Here's the patch.

File Added: 1770224.patch

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Comment By: Don Porter (dgp)
Date: 2007-08-08 15:35

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ok, problem is that when TclGetNumberFromObj()
returns a bignum, it uses some temp space.
The caller is supposed to save the result before
calling again.  The >> implementation code is
not doing so, so when both arguments are bignums,
we end up doing the operation with the second
argument twice.

This not only points the way to fixing this bug;
it points out a whole project of code review to
be done. 

Ick.


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Comment By: Don Porter (dgp)
Date: 2007-08-08 15:07

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ok that last "not broken" example
actually fits in a wide.


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