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  1. JDK
  2. JDK-8015396

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

    Details

    • Subcomponent:
    • Resolved In Build:
      b103
    • CPU:
      x86
    • OS:
      windows
    • Verification:
      Verified

      Description

      Expanded Summary:

      double a%b returns NaN for some (a,b) (|a| < inf, |b|>0)
      But this has so far only been observed on Windows, with 1.6-ish 64-bit VMs, on particular Intel CPUs.
      It has been not-observed across a wide range of other OSes, VMs, and CPUs, but since the cause is unknown, it seems premature to say "can not reproduce".

      (From Jeff Hain)

      While testing some mathematical treatments,
      I had "%" operator on doubles return NaN in
      some cases where the divisor is subnormal
      and the dividend huge.

      More precisely, with
      D(x) = Double.longBitsToDouble(x),

      I had a%b being NaN for:

      - all (a,b) such as
        D(0x7FE0000000000000L) <= |a| <= D(0x7FEFFFFFFFFFFFFFL)
        and
        D(0x0000000000040000L) <= |b| <= D(0x000000000007FFFFL)

      - plus for some values of |b| outside this range,
        when |a| is D(0x7FEFFFFFFFFFFFFFL), like
        b = D(0x000000007FFFFFFFL) (but not for b = D(0x000000007FFEFFFFL))
        b = 6.767486E-317
        b = 7.528725E-318

      Only happens with 64-bit VMs, also happens with -Xint and various flags.
      ------------------------------------------------------------------------------------------------------------------------------
      Observed/not-observed on:

      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
      ------------------------------------------------------------------------------------------------------------------------------
      I have some more non-results, MacOS 10.8.2, Core i5, does not happen with:

      java version "1.6.0_37"
      Java(TM) SE Runtime Environment (build 1.6.0_37-b06-434-11M3909)
      Java HotSpot(TM) 64-Bit Server VM (build 20.12-b01-434, mixed mode)

      java version "1.7.0_13"
      Java(TM) SE Runtime Environment (build 1.7.0_13-b20)
      Java HotSpot(TM) 64-Bit Server VM (build 23.7-b01, mixed mode)

      openjdk version "1.8.0-internal-fastdebug" (near-current jdk8/tl)
      OpenJDK Runtime Environment (build 1.8.0-internal-fastdebug-dr2chase_2013_02_08_16_15-b00)
      OpenJDK 64-Bit Server VM (build 25.0-b17-fastdebug, mixed mode)

      Each above used corresponding javac to compiler ModNaN.java, and plain "java" to test.

      Also tried 7 and 8, class files from 1.6 javac, running java with flags:

      -XX:+TieredCompilation -XX:TieredStopAtLevel=1
      -XX:+TieredCompilation -XX:TieredStopAtLevel=2

      Also tried on MacOS 10.8.2, Core i7, does not happen there with:

      java version "1.6.0_37"
      Java(TM) SE Runtime Environment (build 1.6.0_37-b06-434-11M3909)
      Java HotSpot(TM) 64-Bit Server VM (build 20.12-b01-434, mixed mode)

      ------------------------------------------------------------------------------------------------------------------------------
      Tried Windows 7, core i5, JDK1.7.0_21 and JDK1.6.0_43, with -Xcomp and -Xint and all combinations of
      -XX:UseSSE={0,1,2,3,4,99} and -XX:UseAVX={0,1,2,3,4,99}
      ------------------------------------------------------------------------------------------------------------------------------

      Test code w/ good and bad outputs in comments:

      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);
              }
      ------------------------------------------------------------------------------------------------------------------------------

        Attachments

        1. fp.java
          0.3 kB
        2. ModNaN.java
          2 kB

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              • Assignee:
                ctornqvi Christian Tornqvist
                Reporter:
                drchase David Chase (Inactive)
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                • Created:
                  Updated:
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