sctrcmp-like compare request

[Francisco Olarte]

Seeing a message about potential problems with strcoll in string compare I have noticed that < and <= over strings are not a strict order ( I think strict order is the term, comp-sci guys feel free to correct it ).

I mean using "null-aware strcoll" ( l_strcmp ) means (a<=b and b<=a) does not imply a==b, and conversely (not a<b and not b<a), as == is documented to be based on byte contents.

I realize it is too late for 5.5, and although it is trivial to do it in lua using string.byte() a strcmp-like ( null char aware ) function could be useful ( I mean, memcmp to the minimum of lengths, tie break using lengths ), something like:

-- Untested, just for exposition

-- Although not documented, assume it will continue casting to uchar before pushing.

local sbyte=string.byte

-- More or less what memcp does in c.

function memcmp(s1,s2,l) 

   for i=1 to l do

      local d = sbyte(s1,i)-sbyte(s2,i)

      if d~=0 return d end

   end

   -- return nil, never returns 0 for easier next.

end

function strcmp(s1,s2) 

  -- Checking they are both string left out.

  local l1,l2 = #l1,#l2

  -- memcmp common part, works with embededd nulls

  return memcmp(s1,s2,math.min(l1,l2)) 

  -- Tie break with length.

         or (l1-l2)

end

but coded in C could be useful as an addition to the string module. IMO it would be better to base <= and < on this, to make them coherent with == and move the strcoll stuff to a strcoll method, but it will break some existing code.

Francisco Olarte.