rational.c: implement `Rational#-` in C.

mrbgems/mruby-rational/mrblib/rational.rb

@@ -17,16 +17,6 @@ class Rational < Numeric
     end
   end
 
-  def -(rhs)
-    if rhs.is_a? Rational
-      Rational(numerator * rhs.denominator - rhs.numerator * denominator, denominator * rhs.denominator)
-    elsif rhs.is_a? Integer
-      Rational(numerator - rhs * denominator, denominator)
-    elsif rhs.is_a? Numeric
-      (numerator - rhs * denominator) / denominator
-    end
-  end
-
   def /(rhs)
     if rhs.is_a? Rational
       Rational(numerator * rhs.denominator, denominator * rhs.numerator)

mrbgems/mruby-rational/src/rational.c

@@ -457,8 +457,57 @@ rational_add(mrb_state *mrb, mrb_value x)
   }
 }
 
-mrb_int mrb_num_div_int(mrb_state*, mrb_int, mrb_int);
-mrb_value mrb_complex_new(mrb_state*, mrb_float, mrb_float);
+#ifndef MRB_NO_FLOAT
+mrb_value mrb_complex_new(mrb_state *, mrb_float, mrb_float);
+#endif
+
+static mrb_value
+rational_sub(mrb_state *mrb, mrb_value x)
+{
+  struct mrb_rational *p1 = rational_ptr(mrb, x);
+  mrb_value y = mrb_get_arg1(mrb);
+
+  switch (mrb_type(y)) {
+  case MRB_TT_INTEGER:
+    {
+      mrb_int z = mrb_integer(y);
+      if (mrb_int_mul_overflow(z, p1->denominator, &z)) rat_overflow(mrb);
+      if (mrb_int_sub_overflow(p1->numerator, z, &z)) rat_overflow(mrb);
+      return rational_new_i(mrb, z, p1->denominator);
+    }
+  case MRB_TT_RATIONAL:
+    {
+      struct mrb_rational *p2 = rational_ptr(mrb, y);
+      mrb_int a, b;
+
+      if (mrb_int_mul_overflow(p1->numerator, p2->denominator, &a)) rat_overflow(mrb);
+      if (mrb_int_mul_overflow(p2->numerator, p1->denominator, &b)) rat_overflow(mrb);
+      if (mrb_int_sub_overflow(a, b, &a)) rat_overflow(mrb);
+      if (mrb_int_mul_overflow(p1->denominator, p2->denominator, &b)) rat_overflow(mrb);
+      return rational_new_i(mrb, a, b);
+    }
+
+#if defined(MRB_USE_COMPLEX)
+  case MRB_TT_COMPLEX:
+    x = mrb_complex_new(mrb, rat_to_flo(p1), 0);
+    return mrb_funcall_id(mrb, x, MRB_OPSYM(sub), 1, y);
+#endif
+
+#ifndef MRB_NO_FLOAT
+  case MRB_TT_FLOAT:
+  default:
+    {
+      mrb_float z = p1->numerator - mrb_to_flo(mrb, y) * p1->denominator;
+      return mrb_float_value(mrb, mrb_num_div_flo(mrb, z, (mrb_float)p1->denominator));
+    }
+#else
+  default:
+    mrb_raise(mrb, E_TYPE_ERROR, "non integer subtraction");
+#endif
+  }
+}
+
+mrb_int mrb_num_div_int(mrb_state *, mrb_int, mrb_int);
 
 /* 15.2.8.3.4  */
 /*
@@ -544,6 +593,7 @@ void mrb_mruby_rational_gem_init(mrb_state *mrb)
   mrb_define_method(mrb, rat, "==", rational_eq, MRB_ARGS_REQ(1));
   mrb_define_method(mrb, rat, "-@", rational_minus, MRB_ARGS_NONE());
   mrb_define_method(mrb, rat, "+", rational_add, MRB_ARGS_REQ(1));
+  mrb_define_method(mrb, rat, "-", rational_sub, MRB_ARGS_REQ(1));
   mrb_define_method(mrb, mrb->integer_class, "to_r", fix_to_r, MRB_ARGS_NONE());
   mrb_define_method(mrb, mrb->integer_class, "/", int_div, MRB_ARGS_REQ(1)); /* overrride */
   mrb_define_method(mrb, mrb->integer_class, "quo", int_quo, MRB_ARGS_REQ(1)); /* overrride */