Add BigMath.frexp and ldexp with exponent of 10

See also: ruby/bigdecimal#448

Author: ksss

stdlib/bigdecimal-math/0/big_math.rbs

@@ -172,6 +172,13 @@ module BigMath
   #
   def self?.exp: (BigDecimal, Numeric prec) -> BigDecimal
 
+  # Decomposes +x+ into a normalized fraction and an integral power of ten.
+  #
+  #   BigMath.frexp(BigDecimal(123.456))
+  #   #=> [0.123456e0, 3]
+  #
+  def self?.frexp: (BigDecimal) -> [ BigDecimal, Integer ]
+
   # Computes the gamma function of +decimal+ to the specified number of
   # digits of precision, +numeric+.
   #
@@ -190,6 +197,14 @@ module BigMath
   #
   def self?.hypot: (BigDecimal, BigDecimal, Numeric) -> BigDecimal
 
+  # Inverse of +frexp+.
+  # Returns the value of fraction * 10**exponent.
+  #
+  #   BigMath.ldexp(BigDecimal("0.123456e0"), 3)
+  #   #=> 0.123456e3
+  #
+  def self?.ldexp: (BigDecimal, Integer) -> 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.
   #

test/stdlib/BigMath_test.rb

@@ -82,6 +82,11 @@ def test_exp
                       BigMath, :exp, BigDecimal('1.23'), 10
   end
 
+  def test_frexp
+    assert_send_type "(::BigDecimal) -> [::BigDecimal, ::Integer]",
+                     BigMath, :frexp, BigDecimal(123.456)
+  end
+
   def test_gamma
     assert_send_type "(::BigDecimal, ::Numeric) -> ::BigDecimal",
                      BigMath, :gamma, BigDecimal('0.5'), 32
@@ -92,6 +97,11 @@ def test_hypot
                      BigMath, :hypot, BigDecimal('1'), BigDecimal('2'), 32
   end
 
+  def test_ldexp
+    assert_send_type "(::BigDecimal, ::Integer) -> ::BigDecimal",
+                     BigMath, :ldexp, BigDecimal("0.123456e0"), 3
+  end
+
   def test_lgamma
     assert_send_type "(::BigDecimal, ::Numeric) -> [::BigDecimal, ::Integer]",
                      BigMath, :lgamma, BigDecimal('0.5'), 32
@@ -212,6 +222,11 @@ def test_exp
                       TestClass.new, :exp, BigDecimal('1.23'), 10
   end
 
+  def test_frexp
+    assert_send_type "(::BigDecimal) -> [::BigDecimal, ::Integer]",
+                     TestClass.new, :frexp, BigDecimal(123.456)
+  end
+
   def test_gamma
     assert_send_type "(::BigDecimal, ::Numeric) -> ::BigDecimal",
                      TestClass.new, :gamma, BigDecimal('0.5'), 32
@@ -222,6 +237,11 @@ def test_hypot
                      TestClass.new, :hypot, BigDecimal('1'), BigDecimal('2'), 32
   end
 
+  def test_ldexp
+    assert_send_type "(::BigDecimal, ::Integer) -> ::BigDecimal",
+                     TestClass.new, :ldexp, BigDecimal("0.123456e0"), 3
+  end
+
   def test_lgamma
     assert_send_type "(::BigDecimal, ::Numeric) -> [::BigDecimal, ::Integer]",
                      TestClass.new, :lgamma, BigDecimal('0.5'), 32