Implement Complex#abs in terms of Math.hypot

Math.hypot avoids premature overflow and underflow

mrbgems/mruby-complex/mrblib/complex.rb

@@ -62,7 +62,7 @@ class Complex < Numeric
   end
 
   def abs
-    Math.sqrt(abs2)
+    Math.hypot imaginary, real
   end
   alias_method :magnitude, :abs
 

mrbgems/mruby-complex/test/complex.rb

@@ -70,6 +70,14 @@ end
 assert 'Complex#abs' do
   assert_float Complex(-1).abs,        1
   assert_float Complex(3.0, -4.0).abs, 5.0
+  if 1e39.infinite? then
+    # MRB_USE_FLOAT in effect
+    exp = 125
+  else
+    exp = 1021
+  end
+  assert_true Complex(3.0*2**exp, 4.0*2**exp).abs.finite?
+  assert_float Complex(3.0*2**exp, 4.0*2**exp).abs, 5.0*2**exp
 end
 
 assert 'Complex#abs2' do