Remove unused variable (and add test for it) (#475)

* Remove unused variable (and add test for it)

* Fix shadowing outer local variable warning on ruby-2.5

Author: tompng

lib/bigdecimal/math.rb

@@ -678,9 +678,9 @@ def erfc(x, prec)
     sum = c_prev.add(c_next, prec)
 
     2.step do |k|
-      c = (c_prev.mult(x, prec) + a * c_next).mult(2, prec).mult(x, prec).div(k, prec)
-      sum = sum.add(c, prec)
-      c_prev, c_next = c_next, c
+      cn = (c_prev.mult(x, prec) + a * c_next).mult(2, prec).mult(x, prec).div(k, prec)
+      sum = sum.add(cn, prec)
+      c_prev, c_next = c_next, cn
       break if [c_prev, c_next].all? { |c| c.zero?  || (c.exponent < sum.exponent - prec) }
     end
     value = sum.mult(scale.mult(exp(-(x + a).mult(x + a, prec), prec), prec), prec)
@@ -778,7 +778,6 @@ def lgamma(x, prec)
       # if x is close to 1 or 2, increase precision to reduce loss of significance
       diff1_exponent = (x - 1).exponent
       diff2_exponent = (x - 2).exponent
-      extra_prec = [-diff1_exponent, -diff2_exponent, 0].max
       extremely_near_one = diff1_exponent < -prec2
       extremely_near_two = diff2_exponent < -prec2
 

test/bigdecimal/test_bigmath.rb

@@ -14,6 +14,13 @@ class TestBigMath < Test::Unit::TestCase
   MINF = BigDecimal("-Infinity")
   NAN = BigDecimal("NaN")
 
+  def test_no_warning
+    assert_separately([], "#{<<~"begin;"}\n#{<<~'end;'}")
+    begin;
+      require 'bigdecimal/math'
+    end;
+  end
+
   def test_pi
     assert_equal(
       BigDecimal("3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342117068"),