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

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Bugs item #789290, was opened at 2003-08-15 10:15
Message generated for change (Settings changed) made by rhettinger
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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: Tim Peters (tim_one)
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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