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[Bug math/21094] New: cosf(1.57079697) has 3 ulp error on targets where the generic c code is used
- From: "nszabolcs at gmail dot com" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sourceware dot org
- Date: Mon, 30 Jan 2017 18:34:31 +0000
- Subject: [Bug math/21094] New: cosf(1.57079697) has 3 ulp error on targets where the generic c code is used
- Auto-submitted: auto-generated
https://sourceware.org/bugzilla/show_bug.cgi?id=21094
Bug ID: 21094
Summary: cosf(1.57079697) has 3 ulp error on targets where the
generic c code is used
Product: glibc
Version: 2.24
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: math
Assignee: unassigned at sourceware dot org
Reporter: nszabolcs at gmail dot com
Target Milestone: ---
at x=1.57079697, that is 0x3fc90fe0,
cosf(x) returns -0x1.5777ap-21 instead of -0x1.5777a6p-21
because in sysdeps/ieee754/flt-32/e_rem_pio2f.c
if((ix&0xfffffff0)!=0x3fc90fd0) { /* 24+24 bit pi OK */
...
} else { /* near pi/2, use 24+24+24 bit pi */
...
}
the "near pi/2" special case is not applied.
other than at +-1.57079697, cosf seems to have <= 1 ulp
error compared to cos.
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