Introduce Math.frexp method. (#4560)

crystal-lang · Jun 13, 2017 · 68b1e62 · 68b1e62
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diff --git a/spec/std/math_spec.cr b/spec/std/math_spec.cr
@@ -83,6 +83,11 @@ describe "Math" do
       Math.scalbln(0.11_f32, 2).should be_close(0.44, 1e-7)
       Math.scalbln(0.11, 2).should be_close(0.44, 1e-7)
     end
+
+    it "frexp" do
+      Math.frexp(0.2_f32).should eq({0.8_f32, -2})
+      Math.frexp(0.2).should eq({0.8, -2})
+    end
   end
 
   describe "Logarithms" do

diff --git a/src/math/libm.cr b/src/math/libm.cr
@@ -86,6 +86,8 @@ lib LibM
   fun erf_f64 = erf(value : Float64) : Float64
   fun expm1_f32 = expm1f(value : Float32) : Float32
   fun expm1_f64 = expm1(value : Float64) : Float64
+  fun frexp_f32 = frexpf(value : Float32, exp : Int32*) : Float32
+  fun frexp_f64 = frexp(value : Float64, exp : Int32*) : Float64
   fun gamma_f32 = lgammaf(value : Float32) : Float32
   fun gamma_f64 = lgamma(value : Float64) : Float64
   fun hypot_f32 = hypotf(value1 : Float32, value2 : Float32) : Float32

diff --git a/src/math/math.cr b/src/math/math.cr
@@ -229,6 +229,23 @@ module Math
     scalbln(value.to_f, exp.to_i64)
   end
 
+  # Decomposes given floating point *value* into a normalized fraction and an integral power of two.
+  def frexp(value : Float32)
+    frac = LibM.frexp_f32(value, out exp)
+    {frac, exp}
+  end
+
+  # ditto
+  def frexp(value : Float64)
+    frac = LibM.frexp_f64(value, out exp)
+    {frac, exp}
+  end
+
+  # ditto
+  def frexp(value)
+    frexp(value.to_f)
+  end
+
   # Computes the next highest power of 2 of *v*.
   #
   # ```