Here's another solution:

use strict;
use warnings;

while ( <DATA> ) {
  my ( $args ) = /\@MAC\((.*)\)/;
  my ( $lhs, $v0, $v1, $e ) = split /,/, $args;
  print "$lhs=\n", term( $v0, $v1, [0..$e-1] ), "\n";
}

sub term {
  my $indices = pop;
  my $n = $#$indices;
  if ( $n ) {
    my $m = int($n/2);
    my @t = map term( @_, $_ ),
      [ @{$indices}[0..$m] ], [ @{$indices}[$m+1..$n] ];
    return "($t[0])+($t[1])";
  }
  else {
    my ( $v0, $v1 ) = @_;
    my $first = $indices->[0];
    return "$v0$first*$v1$first";
  }
}
__DATA__
@MAC(Result,A,B,2)
@MAC(output,X,Y,8)
__END__
Result=
(A0*B0)+(A1*B1)
output=
(((X0*Y0)+(X1*Y1))+((X2*Y2)+(X3*Y3)))+(((X4*Y4)+(X5*Y5))+((X6*Y6)+(X7*
+Y7)))
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