[Bug 1292147] [NEW] wrong computation of cos/sin for large angle

[alduc1]

Public bug reported:

With the 2.19 version of eglibc, the library libm computes wrong cosine
and sine for large enough angles.

For exemple, sin(2*pi*0.27*7390843) and sin(2*pi*2.27*7390843) should
give the same result but :

sin(2*pi*0.27*7390843)         =  -0.63742399  OK
sin(2*pi*2.27*7390843)         =   0.63742398  KO

The results should be the same because (2*pi*2.27*7390843) % 2*pi =
2*pi*0.27*7390843.

Another exemple :

cos(2*pi*0.27*7390879)         =  -0.48175367  OK
cos(2*pi*2.27*7390879)         =   0.48175367  KO

 This bug does not occur with 2.18 or previous version of eglibc.

Package details:

Package: libc6
Status: install ok installed
Priority: required
Section: libs
Installed-Size: 10495
Maintainer: Ubuntu Developers <ubuntu-devel-discuss at lists.ubuntu.com>
Architecture: amd64
Multi-Arch: same
Source: eglibc
Version: 2.19-0ubuntu2
Replaces: libc6-amd64
Provides: glibc-2.19-1
Depends: libgcc1
Suggests: glibc-doc, debconf | debconf-2.0, locales
Breaks: hurd (<< 1:0.5.git20140203-1), lsb-core (<= 3.2-27), nscd (<< 2.19)
Conflicts: prelink (<= 0.0.20090311-1), tzdata (<< 2007k-1), tzdata-etch
Conffiles:
 /etc/ld.so.conf.d/x86_64-linux-gnu.conf 593ad12389ab2b6f952e7ede67b8fbbf
Description: Embedded GNU C Library: Shared libraries
 Contains the standard libraries that are used by nearly all programs on
 the system. This package includes shared versions of the standard C library
 and the standard math library, as well as many others.
Homepage: http://www.eglibc.org
Original-Maintainer: GNU Libc Maintainers <debian-glibc at lists.debian.org>

Ubuntu details:
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=14.04
DISTRIB_CODENAME=trusty
DISTRIB_DESCRIPTION="Ubuntu Trusty Tahr (development branch)"

My ubuntu is up to date.

** Affects: eglibc (Ubuntu)
     Importance: Undecided
         Status: New

** Attachment added: "This C code tests cosine and sine values."
   https://bugs.launchpad.net/bugs/1292147/+attachment/4022512/+files/bug_libc6_cos.c

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https://bugs.launchpad.net/bugs/1292147

Title:
  wrong computation of cos/sin for large angle

Status in “eglibc” package in Ubuntu:
  New

Bug description:
  With the 2.19 version of eglibc, the library libm computes wrong
  cosine and sine for large enough angles.

  For exemple, sin(2*pi*0.27*7390843) and sin(2*pi*2.27*7390843) should
  give the same result but :

  sin(2*pi*0.27*7390843)         =  -0.63742399  OK
  sin(2*pi*2.27*7390843)         =   0.63742398  KO

  The results should be the same because (2*pi*2.27*7390843) % 2*pi =
  2*pi*0.27*7390843.

  Another exemple :

  cos(2*pi*0.27*7390879)         =  -0.48175367  OK
  cos(2*pi*2.27*7390879)         =   0.48175367  KO

   This bug does not occur with 2.18 or previous version of eglibc.

  Package details:

  Package: libc6
  Status: install ok installed
  Priority: required
  Section: libs
  Installed-Size: 10495
  Maintainer: Ubuntu Developers <ubuntu-devel-discuss at lists.ubuntu.com>
  Architecture: amd64
  Multi-Arch: same
  Source: eglibc
  Version: 2.19-0ubuntu2
  Replaces: libc6-amd64
  Provides: glibc-2.19-1
  Depends: libgcc1
  Suggests: glibc-doc, debconf | debconf-2.0, locales
  Breaks: hurd (<< 1:0.5.git20140203-1), lsb-core (<= 3.2-27), nscd (<< 2.19)
  Conflicts: prelink (<= 0.0.20090311-1), tzdata (<< 2007k-1), tzdata-etch
  Conffiles:
   /etc/ld.so.conf.d/x86_64-linux-gnu.conf 593ad12389ab2b6f952e7ede67b8fbbf
  Description: Embedded GNU C Library: Shared libraries
   Contains the standard libraries that are used by nearly all programs on
   the system. This package includes shared versions of the standard C library
   and the standard math library, as well as many others.
  Homepage: http://www.eglibc.org
  Original-Maintainer: GNU Libc Maintainers <debian-glibc at lists.debian.org>

  Ubuntu details:
  DISTRIB_ID=Ubuntu
  DISTRIB_RELEASE=14.04
  DISTRIB_CODENAME=trusty
  DISTRIB_DESCRIPTION="Ubuntu Trusty Tahr (development branch)"

  My ubuntu is up to date.

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