Optimize Uni.list

- Use custom iterator with .push-all and .[count|bool]-only
- Makes reifying 15x faster and .count-only 653x faster (on 10000-char str)
- Speeds up Str.ords

src/core/Uni.pm

@@ -14,12 +14,42 @@ my class Uni does Positional[uint32] does Stringy is repr('VMArray') is array_ty
     }
 
     method list(Uni:D:) {
-        gather {
-            my int $n = nqp::elems(self);
-            loop (my int $i = 0; $i < $n; $i = $i + 1) {
-                take nqp::atpos_i(self, $i);
+        Seq.new: class :: does Iterator {
+            has $!uni;
+            has int $!els;
+            has int $!i;
+            method !SET-SELF(\uni) {
+                $!uni := uni;
+                $!i    = -1;
+                $!els  = nqp::elems(uni);
+                self
             }
-        }
+            method new (\uni) { nqp::create(self)!SET-SELF: uni }
+            method pull-one {
+                nqp::if(
+                  nqp::islt_i(($!i = nqp::add_i($!i, 1)), $!els),
+                  nqp::atpos_i($!uni, $!i),
+                  IterationEnd)
+            }
+            method push-all($target --> IterationEnd) {
+                nqp::stmts(
+                  (my     $uni := $!uni), # lexicals faster than attrs
+                  (my int $els  = $!els),
+                  (my int $i    = $!i),
+                  nqp::while(
+                    nqp::islt_i(($i = nqp::add_i($i, 1)), $els),
+                    $target.push: nqp::atpos_i($uni, $i)),
+                  ($!i = $i))
+            }
+            method count-only {
+                nqp::p6box_i(
+                  nqp::if(
+                    nqp::islt_i($!i, nqp::elems($!uni)),
+                    nqp::sub_i(nqp::elems($!uni), nqp::add_i($!i, 1)),
+                    0))
+            }
+            method bool-only { nqp::p6bool(self.count-only) }
+        }.new: self
     }
 
     method Uni(Uni:D:) {