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[Octave-bug-tracker] [bug #54572] int64 does not saturate correctly in n
From: |
Rik |
Subject: |
[Octave-bug-tracker] [bug #54572] int64 does not saturate correctly in negative direction |
Date: |
Tue, 28 Aug 2018 16:12:45 -0400 (EDT) |
User-agent: |
Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:61.0) Gecko/20100101 Firefox/61.0 |
Follow-up Comment #14, bug #54572 (project octave):
jwe's test case fails for -O2, but works for other optimization levels. I
also verified that OCTAVE_HAVE_FAST_INT_OPS must be defined to show the bug.
There are two places where OCTAVE_HAVE_FAST_INT_OPS is checked. I ruled out
one with testing. This leaves this bit of code as the problem:
static T
add (T x, T y)
{
#if defined (OCTAVE_HAVE_FAST_INT_OPS)
// The typecasts do nothing, but they are here to prevent an optimizing
// compiler from interfering. Also, the signed operations on small types
// actually return int.
T u = static_cast<UT> (x) + static_cast<UT> (y);
T ux = u ^ x;
T uy = u ^ y;
if ((ux & uy) < 0)
{
u = octave_int_base<T>::max_val () + __signbit (~u);
}
return u;
#else
The comment sounds interesting. It specifically says that the casts are there
to prevent an optimizing compiler from interfering, which it seems like it
is.
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- [Octave-bug-tracker] [bug #54572] int64 does not saturate correctly in negative direction, (continued)
- [Octave-bug-tracker] [bug #54572] int64 does not saturate correctly in negative direction, John W. Eaton, 2018/08/28
- [Octave-bug-tracker] [bug #54572] int64 does not saturate correctly in negative direction, Dan Sebald, 2018/08/28
- [Octave-bug-tracker] [bug #54572] int64 does not saturate correctly in negative direction, Dmitri A. Sergatskov, 2018/08/28
- [Octave-bug-tracker] [bug #54572] int64 does not saturate correctly in negative direction, Dan Sebald, 2018/08/28
- [Octave-bug-tracker] [bug #54572] int64 does not saturate correctly in negative direction, Dmitri A. Sergatskov, 2018/08/28
- [Octave-bug-tracker] [bug #54572] int64 does not saturate correctly in negative direction, Dan Sebald, 2018/08/28
- [Octave-bug-tracker] [bug #54572] int64 does not saturate correctly in negative direction, Rik, 2018/08/28
- [Octave-bug-tracker] [bug #54572] int64 does not saturate correctly in negative direction, Dmitri A. Sergatskov, 2018/08/28
- [Octave-bug-tracker] [bug #54572] int64 does not saturate correctly in negative direction, Dan Sebald, 2018/08/28
- [Octave-bug-tracker] [bug #54572] int64 does not saturate correctly in negative direction, John W. Eaton, 2018/08/28
- [Octave-bug-tracker] [bug #54572] int64 does not saturate correctly in negative direction,
Rik <=
- [Octave-bug-tracker] [bug #54572] int64 does not saturate correctly in negative direction, Dan Sebald, 2018/08/28
- [Octave-bug-tracker] [bug #54572] int64 does not saturate correctly in negative direction, John W. Eaton, 2018/08/28
- [Octave-bug-tracker] [bug #54572] int64 does not saturate correctly in negative direction, Dan Sebald, 2018/08/28
- [Octave-bug-tracker] [bug #54572] int64 does not saturate correctly in negative direction, Rik, 2018/08/28
- [Octave-bug-tracker] [bug #54572] int64 does not saturate correctly in negative direction, Dan Sebald, 2018/08/28
- [Octave-bug-tracker] [bug #54572] int64 does not saturate correctly in negative direction, John W. Eaton, 2018/08/28
- [Octave-bug-tracker] [bug #54572] int64 does not saturate correctly in negative direction, Dan Sebald, 2018/08/28
- [Octave-bug-tracker] [bug #54572] int64 does not saturate correctly in negative direction, Rik, 2018/08/28
- [Octave-bug-tracker] [bug #54572] int64 does not saturate correctly in negative direction, Dan Sebald, 2018/08/28
- [Octave-bug-tracker] [bug #54572] int64 does not saturate correctly in negative direction, Rik, 2018/08/28