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[Bug math/3268] New: fma for soft-fp is not correct.
- From: "sjmunroe at us dot ibm dot com" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sources dot redhat dot com
- Date: 26 Sep 2006 21:22:34 -0000
- Subject: [Bug math/3268] New: fma for soft-fp is not correct.
- Reply-to: sourceware-bugzilla at sourceware dot org
The current ./math/s_fma[fl].c implementation simply implements:
double
__fma (double x, double y, double z)
{
return (x * y) + z;
}
Which does mot meet the requirement of 754r
"fused multiply-add: The operation fma(x,y,z) computes (x ×y )+z as if with
unbounded range and precision, rounding only once to the destination format; see
subclause 5.1."
This implies (for example) that for double that the 106 bit result of the
multiply be passed unrounded to the add (53 bit) and then final result found to
53 bits.
--
Summary: fma for soft-fp is not correct.
Product: glibc
Version: 2.4
Status: NEW
Severity: normal
Priority: P2
Component: math
AssignedTo: aj at suse dot de
ReportedBy: sjmunroe at us dot ibm dot com
CC: glibc-bugs at sources dot redhat dot com
http://sourceware.org/bugzilla/show_bug.cgi?id=3268
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