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* [Bug math/15536] New: ulp (0x0.0p0) is not FP_SUBNORMAL!
@ 2013-05-26 9:29 schwab@linux-m68k.org
2013-05-26 9:30 ` [Bug math/15536] " schwab@linux-m68k.org
` (5 more replies)
0 siblings, 6 replies; 7+ messages in thread
From: schwab@linux-m68k.org @ 2013-05-26 9:29 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=15536
Bug ID: 15536
Summary: ulp (0x0.0p0) is not FP_SUBNORMAL!
Product: glibc
Version: 2.18
Status: NEW
Severity: normal
Priority: P2
Component: math
Assignee: unassigned at sourceware dot org
Reporter: schwab@linux-m68k.org
CC: carlos at redhat dot com
Target: powerpc*-*-*
The IBM long double version of ulp(0) returns 0, because scalbnl(1,-1127) is 0.
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* [Bug math/15536] ulp (0x0.0p0) is not FP_SUBNORMAL!
2013-05-26 9:29 [Bug math/15536] New: ulp (0x0.0p0) is not FP_SUBNORMAL! schwab@linux-m68k.org
@ 2013-05-26 9:30 ` schwab@linux-m68k.org
2013-05-27 17:31 ` carlos at redhat dot com
` (4 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: schwab@linux-m68k.org @ 2013-05-26 9:30 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=15536
Andreas Schwab <schwab@linux-m68k.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |2.18
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* [Bug math/15536] ulp (0x0.0p0) is not FP_SUBNORMAL!
2013-05-26 9:29 [Bug math/15536] New: ulp (0x0.0p0) is not FP_SUBNORMAL! schwab@linux-m68k.org
2013-05-26 9:30 ` [Bug math/15536] " schwab@linux-m68k.org
@ 2013-05-27 17:31 ` carlos at redhat dot com
2013-05-31 5:39 ` carlos at redhat dot com
` (3 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: carlos at redhat dot com @ 2013-05-27 17:31 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=15536
Carlos O'Donell <carlos at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Assignee|unassigned at sourceware dot org |carlos at redhat dot com
--- Comment #1 from Carlos O'Donell <carlos at redhat dot com> ---
Fixing this ASAP.
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* [Bug math/15536] ulp (0x0.0p0) is not FP_SUBNORMAL!
2013-05-26 9:29 [Bug math/15536] New: ulp (0x0.0p0) is not FP_SUBNORMAL! schwab@linux-m68k.org
2013-05-26 9:30 ` [Bug math/15536] " schwab@linux-m68k.org
2013-05-27 17:31 ` carlos at redhat dot com
@ 2013-05-31 5:39 ` carlos at redhat dot com
2013-05-31 19:28 ` joseph at codesourcery dot com
` (2 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: carlos at redhat dot com @ 2013-05-31 5:39 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=15536
Carlos O'Donell <carlos at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |joseph at codesourcery dot com
--- Comment #2 from Carlos O'Donell <carlos at redhat dot com> ---
Is there a publicly available standard that describes IBM extended precision
long doubles?
The smallest value I can compute is 2^(-1075):
4.94065645841246544177e-324
0x0.00000000000010000000p-1022
The smallest computed value matches the AIX expectations for the, I assume,
similar type.
I'm going to go with the smallest computed value as ulp of zero.
Why?
Because the first double represents the number, and if it's mantissa is zero
and the exponent is zero, then it's zero. The extra precision from the second
double is useless for subnormal values. Therefore the smallest subnormal is
identical to that for double.
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* [Bug math/15536] ulp (0x0.0p0) is not FP_SUBNORMAL!
2013-05-26 9:29 [Bug math/15536] New: ulp (0x0.0p0) is not FP_SUBNORMAL! schwab@linux-m68k.org
` (2 preceding siblings ...)
2013-05-31 5:39 ` carlos at redhat dot com
@ 2013-05-31 19:28 ` joseph at codesourcery dot com
2013-06-03 20:23 ` carlos at redhat dot com
2014-06-13 17:36 ` fweimer at redhat dot com
5 siblings, 0 replies; 7+ messages in thread
From: joseph at codesourcery dot com @ 2013-05-31 19:28 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=15536
--- Comment #3 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
On Fri, 31 May 2013, carlos at redhat dot com wrote:
> Is there a publicly available standard that describes IBM extended precision
> long doubles?
libgcc/config/rs6000/ibm-ldouble-format in a GCC source tree.
> The smallest value I can compute is 2^(-1075):
> 4.94065645841246544177e-324
> 0x0.00000000000010000000p-1022
You have an off-by-one error there. It's 0x1p-1074.
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* [Bug math/15536] ulp (0x0.0p0) is not FP_SUBNORMAL!
2013-05-26 9:29 [Bug math/15536] New: ulp (0x0.0p0) is not FP_SUBNORMAL! schwab@linux-m68k.org
` (3 preceding siblings ...)
2013-05-31 19:28 ` joseph at codesourcery dot com
@ 2013-06-03 20:23 ` carlos at redhat dot com
2014-06-13 17:36 ` fweimer at redhat dot com
5 siblings, 0 replies; 7+ messages in thread
From: carlos at redhat dot com @ 2013-06-03 20:23 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=15536
Carlos O'Donell <carlos at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |FIXED
--- Comment #4 from Carlos O'Donell <carlos at redhat dot com> ---
Resolved.
commit 8b0ccb2d7fd1ec646a622a16bd64e356739ffca3
Author: Carlos O'Donell <carlos@redhat.com>
Date: Mon Jun 3 14:49:48 2013 -0400
BZ #15536: Fix ulp for 128-bit IBM long double.
In 128-bit IBM long double the precision of the type
decreases as you approach subnormal numbers, equaling
that of a double for subnormal numbers. Therefore
adjust the computation in ulp to use 2^(MIN_EXP - MANT_DIG)
which is correct for FP_SUBNORMAL for all types.
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* [Bug math/15536] ulp (0x0.0p0) is not FP_SUBNORMAL!
2013-05-26 9:29 [Bug math/15536] New: ulp (0x0.0p0) is not FP_SUBNORMAL! schwab@linux-m68k.org
` (4 preceding siblings ...)
2013-06-03 20:23 ` carlos at redhat dot com
@ 2014-06-13 17:36 ` fweimer at redhat dot com
5 siblings, 0 replies; 7+ messages in thread
From: fweimer at redhat dot com @ 2014-06-13 17:36 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=15536
Florian Weimer <fweimer at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Flags| |security-
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2013-05-26 9:29 [Bug math/15536] New: ulp (0x0.0p0) is not FP_SUBNORMAL! schwab@linux-m68k.org
2013-05-26 9:30 ` [Bug math/15536] " schwab@linux-m68k.org
2013-05-27 17:31 ` carlos at redhat dot com
2013-05-31 5:39 ` carlos at redhat dot com
2013-05-31 19:28 ` joseph at codesourcery dot com
2013-06-03 20:23 ` carlos at redhat dot com
2014-06-13 17:36 ` fweimer at redhat dot com
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