[llvm-bugs] [Bug 51396] New: __divdf3 returns zero with some extreme values

via llvm-bugs llvm-bugs at lists.llvm.org
Fri Aug 6 19:03:12 PDT 2021


            Bug ID: 51396
           Summary: __divdf3 returns zero with some extreme values
           Product: compiler-rt
           Version: 11.0
          Hardware: Other
                OS: other
            Status: NEW
          Severity: normal
          Priority: P
         Component: compiler-rt
          Assignee: unassignedbugs at nondot.org
          Reporter: aykevanlaethem at gmail.com
                CC: llvm-bugs at lists.llvm.org

I've found that __divdf3 returns an incorrect result for a specific input.

    a = 1.7112092293746032e-193 (raw bits: 0x17E8FBBB7CBDC600)
    b = 8.858903059828881e+116  (raw bits: 0x58367bbed68d8223)
    result = __divdf3(a, b)

I've found that the output is 0, while all hardware implementations I've tested
this code with return a non-zero value: 1.9316265431712e-310 (raw bits:
0x0000238ee05c879e). Therefore, I think this is a bug in __divdf3.

In practice, this issue causes the math package in Go to fail the tests when
compiled with TinyGo and when using the compiler-rt library on a baremetal

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