range.c: implement (part of) `Range#to_a` in C.

Mostly for performance reason.

mrblib/range.rb

@@ -79,8 +79,18 @@ class Range
     h
   end
 
+  ##
+  # call-seq:
+  #    rng.to_a                   -> array
+  #    rng.entries                -> array
+  #
+  # Returns an array containing the items in the range.
+  #
+  #   (1..7).to_a  #=> [1, 2, 3, 4, 5, 6, 7]
+  #   (1..).to_a   #=> RangeError: cannot convert endless range to an array
   def to_a
-    raise RangeError, "cannot convert endless range to an array" if self.last.nil?
+    a = __num_to_a
+    return a if a
     super
   end
   alias entries to_a

src/range.c

@@ -342,6 +342,55 @@ range_initialize_copy(mrb_state *mrb, mrb_value copy)
   return copy;
 }
 
+static mrb_value
+range_num_to_a(mrb_state *mrb, mrb_value range)
+{
+  struct RRange *r = mrb_range_ptr(mrb, range);
+  mrb_value beg = RANGE_BEG(r);
+  mrb_value end = RANGE_END(r);
+  mrb_value ary;
+
+  if (mrb_nil_p(end)) {
+    mrb_raise(mrb, E_RANGE_ERROR, "cannot convert endless range to an array");
+  }
+  if (mrb_integer_p(beg)) {
+    if (mrb_integer_p(end)) {
+      mrb_int a = mrb_integer(beg);
+      mrb_int b = mrb_integer(end);
+      mrb_int len = b - a;
+
+      if (!RANGE_EXCL(r)) len++;
+      ary = mrb_ary_new_capa(mrb, len);
+      for (mrb_int i=0; i<len; i++) {
+        mrb_ary_push(mrb, ary, mrb_int_value(mrb, a+i));
+      }
+      return ary;
+    }
+#ifndef MRB_NO_FLOAT
+    if (mrb_float_p(end)) {
+      mrb_float a = (mrb_float)mrb_integer(beg);
+      mrb_float b = mrb_float(end);
+
+      ary = mrb_ary_new_capa(mrb, (mrb_int)(b - a) + 1);
+      if (RANGE_EXCL(r)) {
+        while (a < b) {
+          mrb_ary_push(mrb, ary, mrb_int_value(mrb, a));
+          a += 1.0;
+        }
+      }
+      else {
+        while (a <= b) {
+          mrb_ary_push(mrb, ary, mrb_int_value(mrb, a));
+          a += 1.0;
+        }
+      }
+      return ary;
+    }
+#endif
+  }
+  return mrb_nil_value();
+}
+
 mrb_value
 mrb_get_values_at(mrb_state *mrb, mrb_value obj, mrb_int olen, mrb_int argc, const mrb_value *argv, mrb_value (*func)(mrb_state*, mrb_value, mrb_int))
 {
@@ -456,4 +505,5 @@ mrb_init_range(mrb_state *mrb)
   mrb_define_method(mrb, r, "inspect",         range_inspect,         MRB_ARGS_NONE()); /* 15.2.14.4.13(x) */
   mrb_define_method(mrb, r, "eql?",            range_eql,             MRB_ARGS_REQ(1)); /* 15.2.14.4.14(x) */
   mrb_define_method(mrb, r, "initialize_copy", range_initialize_copy, MRB_ARGS_REQ(1)); /* 15.2.14.4.15(x) */
+  mrb_define_method(mrb, r, "__num_to_a",      range_num_to_a,        MRB_ARGS_NONE());
 }