my @diffs = diff( ... );
while( @diffs ) {
    my( $x, $y ) = ( pop @diffs, pop @diffs );
    ## use em.
}

##</code><code>##

U32 len = sizeof( U32 ) * some over estimate;
U32 *diffs =  malloc( len );
U32 i = 0;
SV *packed;

SvPV_Set( packed, diffs ); SvLEN_set( len )

for( ) {
    for( ) {
        diffs[ i++ ] = x;
        diffs[ i++ ] = y;
    {
}

SvCur_set( packed, ( i-1 ) * sizeof( U32 ) );

return packed; // sv_2mortal?

##</code><code>##

my $diffs = diff( ... );

while( length( $diffs ) ) {
    my( $x, $y ) = unpack 'VV', substr( $diffs, 0, 8, '' );
    ## use em.
}