/* from op.c */

if (ckWARN(WARN_VOID)) {
  useless = "a constant";  
  /* the constants 0 and 1 are permitted as they are
     conventionally used as dummies in constructs like
     1 while some_condition_with_side_effects;  */  
  if (SvNIOK(sv) && (SvNV(sv) == 0.0 || SvNV(sv) == 1.0))
    useless = 0;
  else if (SvPOK(sv)) {
    /* perl4's way of mixing documentation and code
       (before the invention of POD) was based on a
       trick to mix nroff and perl code. The trick was
       built upon these three nroff macros being used in
       void context. The pink camel has the details in   
       the script wrapman near page 319. */
    if (strnEQ(SvPVX(sv), "di", 2) ||
        strnEQ(SvPVX(sv), "ds", 2) ||
        strnEQ(SvPVX(sv), "ig", 2))
          useless = 0;
  }
}