Tr : double a%b returns NaN for some (a,b) (|a| < inf, |b|>0)

[Jeff Hain]

Vladimir wrote:
>First, could you show what java versions you tried (java -version)? And what OS you are using?


On Windows 7/Core i7 980X, it happens with the following 64 bits versions of Java:
- 1.5.0_22-b03
- 1.6.0_21-ea-b05
- 1.6.0_29-ea-b08 (and also crashes at some point but this version seems to crash a lot, so might be unrelated)
- 1.6.0_38-b05 ("Java HotSpot(TM) 64-Bit Server VM")
but not with:
- 1.7.0_11-b21
- 1.8.0-ea-b73


On Windows XP/T2300, it does not happen with:
- 1.6.0_38
- 1.6.0_39
- 1.7.0_10



>Second, could you try to run with -Xint? It will run in Interpreter mode only without JIT compilation.

Still happens.



>Third, run only Client (-client) or Server (-server) VM. It will use different JIT compilers.
>Note, that there is no Client 64bit VM. If you have latest jdk7update (7u10 or 7u12) or jdk8 you can specify next flags to use only Client's JIT compiler: -XX:+TieredCompilation -XX:TieredStopAtLevel=1.

Only using 64 bits VMs.



Here is some code that can reproduce the problem,
and the output I get whether it happens or not:



public class ModNaN {
    /* Windows 7/Core i7 980X/1.6.0_38 (64):
NaNs
8.98846567431158E307 % 1.295163E-318 = NaN
1.7976931348623157E308 % 2.59032E-318 = NaN
1.7976931348623157E308 % 1.060997895E-314 = NaN
1.7976931348623157E308 % 6.767486E-317 = NaN
1.7976931348623157E308 % 7.528725E-318 = NaN
non-NaNs
8.98846567431158E307 % 1.29516E-318 = 2.53E-321
1.7976931348623157E308 % 2.590327E-318 = 0.0
1.7976931348623157E308 % 1.060965516E-314 = 9.35818525E-315
     */
    /* Windows 7/Core i7 980X/1.7.0_11 (64):
NaNs
8.98846567431158E307 % 1.295163E-318 = 0.0
1.7976931348623157E308 % 2.59032E-318 = 2.57135E-318
1.7976931348623157E308 % 1.060997895E-314 = 5.31535078E-315
1.7976931348623157E308 % 6.767486E-317 = 1.142612E-317
1.7976931348623157E308 % 7.528725E-318 = 4.64634E-318
non-NaNs
8.98846567431158E307 % 1.29516E-318 = 2.53E-321
1.7976931348623157E308 % 2.590327E-318 = 0.0
1.7976931348623157E308 % 1.060965516E-314 = 9.35818525E-315
     */
    public static void main(String[] args) {
        System.out.println("NaNs");
        for (double[] ab : new double[][]{
                new double[]{Double.longBitsToDouble(0x7FE0000000000000L),Double.longBitsToDouble(0x0000000000040000L)},
                new double[]{Double.longBitsToDouble(0x7FEFFFFFFFFFFFFFL),Double.longBitsToDouble(0x000000000007FFFFL)},
                //
                new double[]{Double.longBitsToDouble(0x7FEFFFFFFFFFFFFFL),Double.longBitsToDouble(0x000000007FFFFFFFL)},
                new double[]{Double.longBitsToDouble(0x7FEFFFFFFFFFFFFFL),6.767486E-317},
                new double[]{Double.longBitsToDouble(0x7FEFFFFFFFFFFFFFL),7.528725E-318},
        }) {
            double a = ab[0];
            double b = ab[1];
            double mod = a % b;
            System.out.println(a+" % "+b+" = "+mod);
        }

        System.out.println("non-NaNs");
        for (double[] ab : new double[][]{
                new double[]{Double.longBitsToDouble(0x7FE0000000000000L),Double.longBitsToDouble(0x000000000003FFFFL)},
                new double[]{Double.longBitsToDouble(0x7FEFFFFFFFFFFFFFL),Double.longBitsToDouble(0x0000000000080000L)},
                //
                new double[]{Double.longBitsToDouble(0x7FEFFFFFFFFFFFFFL),Double.longBitsToDouble(0x000000007FFEFFFFL)},
        }) {
            double a = ab[0];
            double b = ab[1];
            double mod = a % b;
            System.out.println(a+" % "+b+" = "+mod);
        }
    }
}



-Jeff