[Chicken-users] two minor tweaks to runtime.c

[Jörg F . Wittenberger]

While I've been looking at the code I wondered if the C compiler
will fur sure pull that one test out of the for-loop.

Maybe it's better no have it there at the first place.
IMHO the code is not more confusing to read this way and should
run better in case the C compiler is not smart enough.

The two spots are in runtime.c C_a_i_list and C_h_list.

In this case a diff seems worse to me than a citation;
The current code is:

C_word C_a_i_list(C_word **a, int c, ...)
{
 va_list v;
 C_word x, last, current,
        first = C_SCHEME_END_OF_LIST;

 va_start(v, c);

 for(last = C_SCHEME_UNDEFINED; c--; last = current) {
   x = va_arg(v, C_word);
   current = C_a_pair(a, x, C_SCHEME_END_OF_LIST);

   if(last != C_SCHEME_UNDEFINED)
     C_set_block_item(last, 1, current);
   else first = current;
 }

 va_end(v);
 return first;
}

Here my current (tested) replacement:


C_word C_a_i_list(C_word **a, int c, ...)
{
 va_list v;
 C_word x, last, current, first;

 va_start(v, c);

 if(c--) {
   x = va_arg(v, C_word);
   first = last = C_a_pair(a, x, C_SCHEME_END_OF_LIST);
   for(; c--; last = current) {
     x = va_arg(v, C_word);
     current = C_a_pair(a, x, C_SCHEME_END_OF_LIST);

     C_set_block_item(last, 1, current);
   }
 } else {
   first = C_SCHEME_END_OF_LIST;
 }

 va_end(v);
 return first;
}


C_word C_h_list(int c, ...)
{
 /* Similar to C_a_i_list(), but put slots with nursery data into mutation 
stack: */
 va_list v;
 C_word x, last, current, first;

 va_start(v, c);

 if(c--) {
   x = va_arg(v, C_word);
   first = last = C_a_pair(C_heaptop, x, C_SCHEME_END_OF_LIST);
   for(; c--; last = current) {
     x = va_arg(v, C_word);
     current = C_a_pair(C_heaptop, x, C_SCHEME_END_OF_LIST);

     if(C_in_stackp(x)) 
	C_mutate(&C_u_i_car(current), x);

     C_set_block_item(last, 1, current);
   }
 } else {
   first = C_SCHEME_END_OF_LIST;
 }

 va_end(v);
 return first;
}

Note that I'm tempted to move the va_start/va_end into the "if".
I'm just unsure whether or not that's allowed by C standards.
(But I can't see how it could harm.)

/Jörg