[Bug other/55560] fesetround(FE_DOWNWARD) causes cos() to return values outside the range of -1 to +1

[pj at ecstaticlyrics dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55560



--- Comment #2 from pj at ecstaticlyrics dot com 2012-12-02 09:10:35 UTC ---

GNU C Library (Ubuntu EGLIBC 2.15-0ubuntu20) stable release version 2.15



I downloaded glibc 2.16, but it encounters an error while compiling.

[Bug other/55560] New: fesetround(FE_DOWNWARD) causes cos() to return values outside the range of -1 to +1

[pj at ecstaticlyrics dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55560



 Bug #: 55560

   Summary: fesetround(FE_DOWNWARD) causes cos() to return values

outside the range of -1 to +1

Classification: Unclassified

   Product: gcc

   Version: 4.7.2

Status: UNCONFIRMED

  Severity: major

  Priority: P3

 Component: other

AssignedTo: unassig...@gcc.gnu.org

ReportedBy: p...@ecstaticlyrics.com





Created attachment 28852

  -- http://gcc.gnu.org/bugzilla/attachment.cgi?id=28852

Contents of /proc/cpuinfo



Simple test program:



#include stdio.h

#include math.h

#include fenv.h



void main() {

  double a, c;

  fesetround(FE_DOWNWARD);

  for (a = -M_PI; a = +M_PI; a += 0.01) {

c = cos(a);

if (c  -1.0 || c  +1.0) {

  printf(cos(%f) is not %f\n, a, c);

};

  };

};



Compile like so: gcc -o test test.c -lm



Expected output is nothing at all, since cos() always returns values between

-1.0 and +1.0.  The actual output, however, is 20,009 lines.  Here are the

first ten:



cos(-3.141593) is not -1.000485

cos(2.430171) is not 3614403565883090812337301068370710204239577088.00

cos(2.430172) is not 195176399637579483727029815821181674649563430912.00

cos(2.430173) is not 386738395709080693943503989636585388708949131264.00

cos(2.430174) is not 578300391780195078044017318793663580791807934464.00

cos(2.430175) is not 769862387850731413470826575343659276213015281664.00

cos(2.430176) is not 961424383920497666369804385270998542397395173376.00

cos(2.430177) is not 1152986379989302370794292276806879317292807618560.00

cos(2.430178) is not 1344548376056954223056908607395862930425122914304.00

cos(2.430179) is not 1536110372123261919470271734482510711320211357696.00



The problem disappears if the test program is compiled with -m32 or if

fesetround(FE_DOWNWARD) is removed.