Add BigMath.gamma and BigMath.lgamma

See also: ruby/bigdecimal#451

Author: ksss

stdlib/bigdecimal-math/0/big_math.rbs

@@ -172,6 +172,14 @@ module BigMath
   #
   def self?.exp: (BigDecimal, Numeric prec) -> BigDecimal
 
+  # Computes the gamma function of +decimal+ to the specified number of
+  # digits of precision, +numeric+.
+  #
+  #   BigMath.gamma(BigDecimal('0.5'), 32).to_s
+  #   #=> "0.17724538509055160272981674833411e1"
+  #
+  def self?.gamma: (BigDecimal, Numeric) -> BigDecimal
+
   # <!--
   #   rdoc-file=ext/bigdecimal/bigdecimal.c
   # Returns sqrt(x**2 + y**2) to the specified number of digits of precision,
@@ -182,6 +190,14 @@ module BigMath
   #
   def self?.hypot: (BigDecimal, BigDecimal, Numeric) -> BigDecimal
 
+  # Computes the natural logarithm of the absolute value of the gamma function
+  # of +decimal+ to the specified number of digits of precision, +numeric+ and its sign.
+  #
+  #   BigMath.lgamma(BigDecimal('0.5'), 32)
+  #   #=> [0.57236494292470008707171367567653e0, 1]
+  #
+  def self?.lgamma: (BigDecimal, Numeric) -> [BigDecimal, Integer]
+
   #   - BigMath.log(decimal, numeric)    -> BigDecimal
   # -->
   # Computes the natural logarithm of `decimal` to the specified number of digits

test/stdlib/BigMath_test.rb

@@ -26,7 +26,7 @@ def test_acosh
     assert_send_type "(::BigDecimal, ::Numeric) -> ::BigDecimal",
                      BigMath, :acosh, BigDecimal('2'), 32
   end
-  
+
   def test_asin
     assert_send_type "(::BigDecimal, ::Numeric) -> ::BigDecimal",
                      BigMath, :asin, BigDecimal('0.5'), 32
@@ -82,11 +82,21 @@ def test_exp
                       BigMath, :exp, BigDecimal('1.23'), 10
   end
 
+  def test_gamma
+    assert_send_type "(::BigDecimal, ::Numeric) -> ::BigDecimal",
+                     BigMath, :gamma, BigDecimal('0.5'), 32
+  end
+
   def test_hypot
     assert_send_type "(::BigDecimal, ::BigDecimal, ::Numeric) -> ::BigDecimal",
                      BigMath, :hypot, BigDecimal('1'), BigDecimal('2'), 32
   end
 
+  def test_lgamma
+    assert_send_type "(::BigDecimal, ::Numeric) -> [::BigDecimal, ::Integer]",
+                     BigMath, :lgamma, BigDecimal('0.5'), 32
+  end
+
   def test_log
     assert_send_type  "(::BigDecimal, ::Numeric prec) -> ::BigDecimal",
                       BigMath, :log, BigDecimal('1.23'), 10
@@ -202,11 +212,21 @@ def test_exp
                       TestClass.new, :exp, BigDecimal('1.23'), 10
   end
 
+  def test_gamma
+    assert_send_type "(::BigDecimal, ::Numeric) -> ::BigDecimal",
+                     TestClass.new, :gamma, BigDecimal('0.5'), 32
+  end
+
   def test_hypot
     assert_send_type "(::BigDecimal, ::BigDecimal, ::Numeric) -> ::BigDecimal",
                      TestClass.new, :hypot, BigDecimal('1'), BigDecimal('2'), 32
   end
 
+  def test_lgamma
+    assert_send_type "(::BigDecimal, ::Numeric) -> [::BigDecimal, ::Integer]",
+                     TestClass.new, :lgamma, BigDecimal('0.5'), 32
+  end
+
   def test_log
     assert_send_type  "(::BigDecimal, ::Numeric prec) -> ::BigDecimal",
                       TestClass.new, :log, BigDecimal('1.23'), 10