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  1. JDK
  2. JDK-8189172

Math.pow(base, 2.0) still broken.

    Details

    • Type: Bug
    • Status: Open
    • Priority: P3
    • Resolution: Unresolved
    • Affects Version/s: 8u144
    • Fix Version/s: None
    • Component/s: hotspot
    • Labels:
    • Environment:

      /opt/ts/bin/java -version
      java version "1.8.0_144"
      Java(TM) SE Runtime Environment (build 1.8.0_144-b01)
      Java HotSpot(TM) 64-Bit Server VM (build 25.144-b01, mixed mode)

    • Subcomponent:
    • CPU:
      x86
    • OS:
      linux_ubuntu

      Description

      The following program demonstrates that the x * x optimization when exp == 2 is still broken for jdk-8 (it is fixed on jdk-9):

      public class PowTest {

          public static void main(final String[] args) {
              double b = 1.0 / 3.0;
              double e = 2.0;
              double r = Math.pow(b, e);
              double n = b * b;
              // Find a base where pow(b, 2) != b * b
              while (r == n) {
                      b += 1.0 / 3.0;
                      n = Math.pow(b, e);
                      r = b * b;
              }
              System.out.println("found b=" + b + " n=" + n + " r=" + r);
              r = n = Math.pow(b, e);
              // Wait until pow gets compiled into x * x
              while (r == n) {
                      n = Math.pow(b, e);
              }
              System.out.println("bad b=" + b + " n=" + n + " r=" + r);
          }
      }

      Please fix it (it is causing us a lot of pain to have to deal with the same code producing different numeric results on each run). It would be nice at some point to require in the language that intrinsic math functions produce the same exact results when interpreted and compiled.

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              • Assignee:
                Unassigned
                Reporter:
                christos Christos Zoulas
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                Dates

                • Created:
                  Updated: