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How to locate the first not equal character in two strings

Data manipulation

How to locate the first not equal character in two strings

by  prex1  Posted    (Edited  )
The sub requires two strings as the input and returns:
-1 if the strings are equal or both returning false when used in a boolean op (e.g. undef or length zero or '0', but not '00')
0 if one string is false (as above) and not the other one
the position of the first different character (0 if the first character is not equal, 1 if the second,etc)
Code: 
sub first_nomatch{
  my($sa,$sb)=@_;
  return -1 unless $sa || $sb;
  return 0 unless $sa && $sb;
  return 0 if ord($sa) != ord($sb);
  return -1 if $sa eq $sb;
  my$sc="$sa" ^ "$sb";
  $sc=~/^(\x00+)/;
  return length($1);
}
The double quotes in the 7th line are required only if the strings might ever be passed to the sub as numbers.
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