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[Bug math/15214] New: cacos, casin, and casinh wrongly underflow ldbl-128ibm
- From: "azanella at linux dot vnet.ibm.com" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sourceware dot org
- Date: Thu, 28 Feb 2013 19:33:40 +0000
- Subject: [Bug math/15214] New: cacos, casin, and casinh wrongly underflow ldbl-128ibm
- Auto-submitted: auto-generated
http://sourceware.org/bugzilla/show_bug.cgi?id=15214
Bug #: 15214
Summary: cacos, casin, and casinh wrongly underflow ldbl-128ibm
Product: glibc
Version: 2.17
Status: NEW
Severity: minor
Priority: P2
Component: math
AssignedTo: unassigned@sourceware.org
ReportedBy: azanella@linux.vnet.ibm.com
Classification: Unclassified
The following math/libm-test.inc tests trigger spurious underflows exceptions
for ldbl-128ibm:
cacos (0x1p500 + 1.0 i)
cacos (0x1p500 - 1.0 i)
cacos (-0x1p500 + 1.0 i)
cacos (-0x1p500 - 1.0 i)
cacos (1.0 + 0x1p500 i)
cacos (-1.0 + 0x1p500 i)
cacos (1.0 - 0x1p500 i)
cacos (-1.0 - 0x1p500 i)
casin (0x1p500 + 1.0 i)
casin (0x1p500 - 1.0 i)
casin (-0x1p500 + 1.0 i)
casin (-0x1p500 - 1.0 i)
casin (1.0 + 0x1p500 i)
casin (-1.0 + 0x1p500 i)
casin (1.0 - 0x1p500 i)
casin (-1.0 - 0x1p500 i)
casinh (0x1p500 + 1.0 i)
casinh (0x1p500 - 1.0 i)
casinh (-0x1p500 + 1.0 i)
casinh (-0x1p500 - 1.0 i)
casinh (1.0 + 0x1p500 i)
casinh (-1.0 + 0x1p500 i)
casinh (1.0 - 0x1p500 i)
casinh (-1.0 - 0x1p500 i)
This is in fact an issue with __ieee754_logl implementation: in the domain
reduction phase, where the algorithm transform log(u) -> log(t) + log(u/t) and
log(u/t) -> log(1+(u-t)/t), if the input is high enough the calculation
'1+(u-t)/t' might generate subnormal numbers.
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