Bug 14331

Summary:	csqrt inaccuracy on internal underflows with subnormal argument
Product:	glibc	Reporter:	Joseph Myers <jsm28>
Component:	math	Assignee:	Not yet assigned to anyone <unassigned>
Status:	RESOLVED FIXED
Severity:	normal	Flags:	fweimer: security-
Priority:	P2
Version:	2.16
Target Milestone:	---
Host:		Target:
Build:		Last reconfirmed:

Description Joseph Myers 2012-07-04 16:55:04 UTC

Some internal underflows can cause substantial inaccuracy in the results of csqrt.  Specifically, on x86_64, csqrt (0x1p-1074i) returns zero and csqrt (0x1p-500 + 0x1p-1074i) returns an imaginary part of zero (should be 4.469444793151709302716387622440056066334e-249).

Comment 1 Joseph Myers 2012-07-05 11:04:59 UTC

Fixed for 2.17 by:

commit cdfe2c5eb3703ed964cbfdb6906b21ace2956385
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Thu Jul 5 11:02:13 2012 +0000

    Fix csqrt underflow (bugs 14157, 14331).