Example #30 -- Reference Parameters

<1 arctic:~/Examples >cat swap.cpp

#include <stdio.h>

void swapA( int * X, int * Y )
{
  int Z = *X;
  *X = *Y;
  *Y = Z;
}

void swapB( int & X, int & Y )
{
  int Z = X;
  X = Y;
  Y = Z;
}

/********** hand-written assembly language **********

        .global  swapA

        .section ".text"
        .align   4
swapA:
        save     %sp, -96, %sp

        ld       [%i0], %l0
        ld       [%i1], %l1

        st       %l1, [%i0]
        st       %l0, [%i1]

        ret
        restore

**********/

int main()
{
  int AA = 5, BB = 9;

  printf( "AA: %d  BB: %d\n", AA, BB );

  swapA( &AA, &BB );

  printf( "AA: %d  BB: %d\n", AA, BB );

  swapB( AA, BB );

  printf( "AA: %d  BB: %d\n", AA, BB );
}

<2 arctic:~/Examples >g++ swap.cpp
<3 arctic:~/Examples >a.out
AA: 5  BB: 9
AA: 9  BB: 5
AA: 5  BB: 9



<4 arctic:~/Examples >g++ -S swap.cpp
<5 arctic:~/Examples >cat swap.s

        .section ".text"
        .align   4
        .global  _Z5swapAPiS_
_Z5swapAPiS_:
        save     %sp, -120, %sp
        st       %i0, [%fp+68]
        st       %i1, [%fp+72]
        ld       [%fp+68], %g1
        ld       [%g1], %g1
        st       %g1, [%fp-20]
        ld       [%fp+68], %i5
        ld       [%fp+72], %g1
        ld       [%g1], %g1
        st       %g1, [%i5]
        ld       [%fp+72], %i5
        ld       [%fp-20], %g1
        st       %g1, [%i5]
        ret
        restore
        .align   4
        .global  _Z5swapBRiS_
_Z5swapBRiS_:
        save     %sp, -120, %sp
        st       %i0, [%fp+68]
        st       %i1, [%fp+72]
        ld       [%fp+68], %g1
        ld       [%g1], %g1
        st       %g1, [%fp-20]
        ld       [%fp+68], %i5
        ld       [%fp+72], %g1
        ld       [%g1], %g1
        st       %g1, [%i5]
        ld       [%fp+72], %i5
        ld       [%fp-20], %g1
        st       %g1, [%i5]
        ret
        restore

<6 arctic:~/Examples >g++ -O -S swap.cpp
<7 arctic:~/Examples >cat swap.s

        .section ".text"
        .align   4
        .global  _Z5swapAPiS_
_Z5swapAPiS_:
        ld       [%o0], %o5
        ld       [%o1], %g1
        st       %g1, [%o0]
        retl
        st       %o5, [%o1]
        .align   4
        .global  _Z5swapBRiS_
_Z5swapBRiS_:
        ld       [%o0], %o5
        ld       [%o1], %g1
        st       %g1, [%o0]
        retl
        st       %o5, [%o1]