[ python-Bugs-789290 ] Minor FP bug in object.c

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Bugs item #789290, was opened at 2003-08-15 11:15
Message generated for change (Comment added) made by tim_one
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=105470&aid=789290&group_id=5470

Category: Python Interpreter Core
Group: Python 2.2.3
Status: Open
Resolution: None
Priority: 5
Submitted By: Nick Maclaren (nmm1)
>Assigned to: Nobody/Anonymous (nobody)
Summary: Minor FP bug in object.c

Initial Comment:
This is closely related to the one I have reported
in floatobject.c (789159).  VERY closely.  It is
shown up by the following test on a machine with
64-bit longs and floating-point trapping turned on
(though it might show up as bogus results even with
no trapping):

print int( 9223372036854775200.0)
print int( 9223372036854775800.0)
print int(-9223372036854776800.0)
print int(-9223372036854777000.0)

958,959c958,959
<       double intpart, fractpart;
<       int expo;
---
>       double intpart, fractpart, z;
>       int expo, i, j;
978c978,989
<               if (intpart > LONG_MAX || -intpart >
LONG_MAX) {
---
>               /* Remember that (double)LONG_MAX can
round either way. */
>               if (intpart > LONG_MIN/2 && intpart <
LONG_MAX/2)
>                       z = 0.0;
>               else {
>                       z = (intpart >= 0.0 ? intpart :
-intpart);
>                       for (i =
(sizeof(long)*CHAR_BIT-1)/16; i >= 0; --i) {
>                               x = LONG_MAX;
>                               for (j = 0; j < i; ++j)
x >>= 16;
>                               z -=
ldexp(x&0xffff,16*i);
>                       }
>               }
>               if (z > 0.0) {


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>Comment By: Tim Peters (tim_one)
Date: 2004-02-16 19:22

Message:
Logged In: YES 
user_id=31435

Sorry, I can't make for this, so unassigned it.

To help the next person,

1. Please say something about what "the bug" is.  You show 4 
lines printing int(big_integer), but don't show any output.  In 
addition, the patch *appears* to be against _Py_HashDouble
(), but that function isn't involved in int() or in printing.

2. Please generate a context diff for patches, and attach the 
patch to the bug report instead of pasting it into the text 
box.  SourceForge destroys the intended line structure and 
indentation in text boxes, and this non-context diff patch is 
very hard to follow in this mangled form.

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You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=105470&aid=789290&group_id=5470