[Bug libgcj/16122] New: gij - Incorrect result due to computations in extended precision on x86

[debian-gcc at lists dot debian dot org]

[forwarded from http://bugs.debian.org/255525]

3.3.4 release and 3.4.1 branch, bug submitter writes:

Concerning the following Java source: 
 
------------------------------------------------------------------ 
// $Id: test.java 3734 2004-06-21 15:36:52Z lefevre $ 
 
public class test { 
    public static void main(String[] args) throws Exception { 
        test t = new test(); 
        t.doTest(); 
    } 
 
    volatile double x, y, z, d; 
 
    public void doTest() { 
        x = 9007199254740994.0; /* 2^53 + 2 */ 
        y = 1.0 - 1/65536.0; 
        z = x + y; 
        d = z - x; 
        System.out.println("z = " + z); 
        System.out.println("d = " + d); 
    } 
} 
------------------------------------------------------------------ 
I've compiled it with "gcj -C test.java" (GCC 3.3.4). 
 
Both IBM's and Sun's JVM give the correct result: 
 
greux:~/wd/src/fp> /global/greux/lefevre/IBMJava2-131/jre/bin/java test 
z = 9.007199254740994E15 
d = 0.0 
 
greux:~/wd/src/fp> /usr/local/j2re1.4.1/bin/java test 
z = 9.007199254740994E15 
d = 0.0 
 
but not gij: 
 
greux:~/wd/src/fp> /usr/bin/gij test 
z = 9.007199254740996E15 
d = 2.0 
 
gij should switch the FPU of the x86 processor 
(Pentium III in my case) to rounding in double precision to avoid the 
effect of the "double rounding" (you may find some information about 
this effect here: <http://www.srware.com/linux_numerics.txt>).

-- 
           Summary: gij - Incorrect result due to computations in extended
                    precision on x86
           Product: gcc
           Version: 3.4.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: libgcj
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: debian-gcc at lists dot debian dot org
                CC: gcc-bugs at gcc dot gnu dot org,java-prs at gcc dot gnu
                    dot org
  GCC host triplet: i486-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16122