[bigdecimal] Fix the default precision of Float#to_d

Fix ruby/bigdecimal#70 [Bug #13331] ruby/bigdecimal@aa536cd4b5
ruby · Dec 19, 2020 · e1424c3 · e1424c3
1 parent 4735a5b
commit e1424c3
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Showing 3 changed files with 14 additions and 6 deletions.
diff --git a/ext/bigdecimal/bigdecimal.c b/ext/bigdecimal/bigdecimal.c
@@ -1278,7 +1278,7 @@ BigDecimal_mult(VALUE self, VALUE r)
 
     GUARD_OBJ(a, GetVpValue(self, 1));
     if (RB_TYPE_P(r, T_FLOAT)) {
-	b = GetVpValueWithPrec(r, DBL_DIG+1, 1);
+        b = GetVpValueWithPrec(r, DBLE_FIG, 1);
     }
     else if (RB_TYPE_P(r, T_RATIONAL)) {
 	b = GetVpValueWithPrec(r, a->Prec*VpBaseFig(), 1);

diff --git a/ext/bigdecimal/lib/bigdecimal/util.rb b/ext/bigdecimal/lib/bigdecimal/util.rb
@@ -43,7 +43,7 @@ class Float < Numeric
   #
   # See also BigDecimal::new.
   #
-  def to_d(precision=Float::DIG)
+  def to_d(precision=Float::DIG+1)
     BigDecimal(self, precision)
   end
 end

diff --git a/test/bigdecimal/test_bigdecimal_util.rb b/test/bigdecimal/test_bigdecimal_util.rb
@@ -17,10 +17,12 @@ def test_Integer_to_d
   end
 
   def test_Float_to_d_without_precision
-    delta = 1.0/10**(Float::DIG)
-    assert_in_delta(BigDecimal(0.5, Float::DIG), 0.5.to_d, delta)
-    assert_in_delta(BigDecimal(355.0/113.0, Float::DIG), (355.0/113.0).to_d, delta)
-    assert_equal(9.05.to_d.to_s('F'), "9.05")
+    delta = 1.0/10**(Float::DIG+1)
+    assert_in_delta(BigDecimal(0.5, Float::DIG+1), 0.5.to_d, delta)
+    assert_in_delta(BigDecimal(355.0/113.0, Float::DIG+1), (355.0/113.0).to_d, delta)
+
+    assert_equal(9.05, 9.05.to_d.to_f)
+    assert_equal("9.050000000000001", 9.05.to_d.to_s('F'))
 
     bug9214 = '[ruby-core:58858]'
     assert_equal((-0.0).to_d.sign, -1, bug9214)
@@ -43,6 +45,12 @@ def test_Float_to_d_with_precision
     assert(1.1.to_d(digits).frozen?)
   end
 
+  def test_Float_to_d_bug13331
+    assert_equal(64.4.to_d,
+                 1.to_d * 64.4,
+                 "[ruby-core:80234] [Bug #13331]")
+  end
+
   def test_Rational_to_d
     digits = 100
     delta = 1.0/10**(digits)