Re: Convert big number from decimal to hexadecimal

[ambrus]

Let me implement the other algorithm too. This one is longer, but you could cut some of it if you reorganized it so that there's only one function doing the work of all three.

use 5.010; 
{
no warnings "uninitialized";
sub dadd {
        my($a, $b) = @_; my @b = @$b; my $c;
        for (my $k = 0; @b || $c; $k++) {
                $c = 10 <= ($$a[$k] += $c + shift @b); $$a[$k] %= 10;
        }
}
sub dsub {
        my($a, $b) = @_; my @b = @$b; my $c;
        for (my $k = 0; $k < @$a; $k++) {
                $c = ($$a[$k] -= $c + shift @b) < 0; $$a[$k] += 10 * $
+c;
        }
    $c;
}
sub dcmp {
        my($a, $b) = @_; my @a = @$a; my @b = @$b; my $r;
    while (@a || @b) {
        if (my $t = shift @a <=> shift @b) { $r = $t; }
    }
    $r;
}
}
my $n = [reverse split //, "4335043554366887798866555766"];
my $p = [1];
my $e = 0;
while (0 <= dcmp($n, $p)) { 
        dadd $p, $p for 0..3; $e++;
}
my $r;
for my $_e (0 .. $e - 1) {
        dadd $n, $n for 0..3;
        my $i = 0;
        while (0 <= dcmp ($n, $p)) {
                dsub $n, $p; $i++;
        }
        $r .= sprintf "%x", $i;
}
say $r;
__END__

[ambrus]

Okay, here's it a bit shortened:

use 5.010; 
sub dalu {
        no warnings "uninitialized";
        my($a, $b, $n, $o) = @_; my @b = @$b; my $c = $n && 1;
        for (my $k = 0; @b || $k < @$a || $c && !$n; $k++) {
                my $y = shift @b; $n and $y = 9 - $y;
                $c = 10 <= (my $z = $$a[$k] + $c + $y); 
                $o or $$a[$k] = $z % 10;
        }
        $c;
}
my $n = [reverse split //, "4335043554366887798866555766"];
my $p = [1];
my $e = 0;
while (dalu $n, $p, 1, 1) { 
        dalu $p, $p for 0..3; $e++;
}
my $r;
for my $_e (0 .. $e - 1) {
        dalu $n, $n for 0..3;
        my $i = 0;
        while (dalu $n, $p, 1, 1) {
                dalu $n, $p, 1; $i++;
        }
        $r .= sprintf "%x", $i;
}
say $r;
__END__

Update: made code a bit nicer.