ADD_ATOMIC

 The ADD_ATOMIC function adds the value of an expression  to  the
 value  of  a  variable,  stores  the  newly  computed value, and
 returns the previous value.


 Syntax:

   ADD_ATOMIC(e,v)

 The type of the expression 'e'  must  be  assignment  compatbile
 with  that  of  the  variable  'v'.  The variable 'v' must be an
 INTEGER, UNSIGNED, INTEGER64, or UNSIGNED64 variable and must be
 allocated  on  a  natural boundary (ie, longword for INTEGER and
 UNSIGNED and quadword for INTEGER64 and UNSIGNED64).  The result
 of ADD_ATOMIC is the same type as the variable 'v'.

 Overflow and  subrange  checking  are  never  performed  on  the
 ADD_ATOMIC  operation,  even  if these options are in effect for
 the rest of the function or compilation unit.