Ensure BigMath.sin and BigMath.cos to be within -1..1

Author: tompng

lib/bigdecimal/math.rb

@@ -85,6 +85,7 @@ def sin(x, prec)
       d   = sign * x1.div(z,m)
       y  += d
     end
+    y = BigDecimal("1") if y > 1
     neg ? -y : y
   end
 
@@ -129,7 +130,7 @@ def cos(x, prec)
       d   = sign * x1.div(z,m)
       y  += d
     end
-    y
+    y < -1 ? BigDecimal("-1") : y > 1 ? BigDecimal("1") : y
   end
 
   # call-seq:

test/bigdecimal/test_bigmath.rb

@@ -37,6 +37,8 @@ def test_sin
     assert_in_delta(0.0, sin(PI(N) * 21, N))
     assert_in_delta(0.0, sin(PI(N) * 30, N))
     assert_in_delta(-1.0, sin(PI(N) * BigDecimal("301.5"), N))
+    assert_operator(sin(PI(30) / 2, 30), :<=, 1)
+    assert_operator(sin(-PI(30) / 2, 30), :>=, -1)
   end
 
   def test_cos
@@ -51,6 +53,8 @@ def test_cos
     assert_in_delta(-1.0, cos(PI(N) * 21, N))
     assert_in_delta(1.0, cos(PI(N) * 30, N))
     assert_in_delta(0.0, cos(PI(N) * BigDecimal("301.5"), N))
+    assert_operator(cos(PI(30), 30), :>=, -1)
+    assert_operator(cos(PI(30) * 2, 30), :<=, 1)
   end
 
   def test_atan