Clemson University -- CPSC 231 -- Fall 2009

Multiple entry points

  allows different function names, different parameter lists,
    default parameters, etc.


Example

    int fn( int a = 1, int b = 2 ){
      return( a + b );
    }

  can be written in assembly as

      .global fn_ab, fn_b, fn, sum
    fn_ab:
      mov  1, %o0           /* default first parameter */
    fn_b:
      mov  2, %o1           /* default second parameter */
    fn:
    sum:
      add  %o0, %o1, %o0    /* add parameters and return sum */
      retl
       nop

  with fn()    becoming call fn_ab
       fn(3)   becoming call fn_b    after the caller places 3 in %o0
       fn(4,6) becoming call fn      (or call sum) after the caller
                                       places 4 in %o0 and 6 in %o1

  so that a driver like this

    #include<stdio.h>
    int main(){
      printf("fn_ab() returns %d\n",fn_ab());
      printf("fn_b(3) returns %d\n",fn_b(3));
      printf("fn(4,6) returns %d\n",fn(4,6));
      printf("sum(5,7) returns %d\n",sum(5,7));
      return 0;
    }

  will print

    fn_ab() returns 3
    fn_b(3) returns 5
    fn(4,6) returns 10
    sum(5,7) returns 12


Of course, multiple exit paths are also possible.