PI73827: FAILURE TO RECOGNIZE VALID IEEE754 128-BIT NAN

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• On z/OS, a "long double" NaN can take this form:
  
  
      0x7FFF8000000000000000000000000000
  
  This conforms to IEEE754 NaN encoding:
  
  "In IEEE 754 standard-conforming floating-point storage formats,
  NaNs are identified by specific, pre-defined bit patterns unique
  to NaNs.
  
  The sign bit does not matter. Binary format NaNs are represented
  with the exponential field filled with ones (like infinity
  values) and some non-zero number in the significand field
  (to make them distinct from infinity values)."
  
  In this case, the bit in the 0x80 byte is the "non-zero number
  in the significand field." All is well here.
  
  
  Now, take this slightly modified value:
  
      0x7FFF0000000100000000000000000000
  
  The bit in the 0x80 byte has been cleared, and in its place
  is set an arbitrary bit further down in the significand.
  
  
  z/OS does not recognize this as a NaN. (That is, isnan() returns
  false for this value.)
  This is incorrect, per the definition of how NaNs are encoded.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: Users of XL C/C++ that call function         *
  *                 isnan() to test IEEE754 128-bit NaN.         *
  ****************************************************************
  * PROBLEM DESCRIPTION: An IEEE754 128-bit NaN may not be       *
  *                      identified by function isnan().         *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  See the problem description.
  

Problem conclusion

• The code has been changed to fix the problem.
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

  UI44444 UI44445

Modules/Macros

• CELHCVBF CELQCVBF EDC40456
  

Fix information

• Fixed component name

  LE C LIBRARY

• Fixed component ID

  568819805

Applicable component levels

• R7A0 PSY UI44444

     UP17/02/22 P F702

• R790 PSY UI44445

     UP17/02/22 P F702

Fix is available

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