Add binary search algorithm

src/Algorithm/algorithm.jl

@@ -4,4 +4,6 @@ using Reexport.@reexport
 
 @reexport using SortingAlgorithms
 
+include("binarysearch.jl")
+
 end

src/Algorithm/binarysearch.jl

@@ -0,0 +1,22 @@
+export binarysearch
+
+binarysearch{T<:Integer}(f, z, α::T, β::T) = begin
+    if β - α == 1
+        y = f(α)
+        y == z && return α, α
+        y >  z && throw(DomainError())
+
+        y = f(β)
+        y == z && return β, β
+        y <  z && throw(DomainError())
+
+        return α, β
+    end
+
+    m = (α + β) >> 1
+    y = f(m)
+
+    y > z && return binarysearch(f, z, α, m)
+    y < z && return binarysearch(f, z, m, β)
+    return m, m
+end

test/Algorithm/algorithm.jl

@@ -3,11 +3,12 @@ module Algorithm
 using Brainstorm.Algorithm
 using Base.Test
 
+include("binarysearch.jl")
+
 function test_all()
     println("")
-    print(rpad("Algorithm...", 50, ' '))
 
-    println("PASS")
+    test_binarysearch_all()
 end
 
 end

test/Algorithm/binarysearch.jl

@@ -0,0 +1,11 @@
+function test_binarysearch_all()
+    print(rpad("Algorithm.BinarySearch...", 50, ' '))
+
+    @test [binarysearch(x -> x, i, 1, 100) for i in 1:100] == [(i,i) for i in 1:100]
+    @test [binarysearch(x -> 2x, i, 0, 10) for i in 2:10] == [(1,1); (1,2); (2,2); (2,3); (3,3); (3,4); (4,4); (4,5); (5,5)]
+
+    @test_throws DomainError binarysearch(x -> x, 0, 1, 10)
+    @test_throws DomainError binarysearch(x -> x, 11, 1, 10)
+
+    println("PASS")
+end