Replace broken backports gem Bignum#bit_length with custom monkey-pat…

…ch for MRI < 2.1

I filed the following bug with backports gem:

marcandre/backports#95

Added some tests to cover this function, but they will only be using
the backport version if the current Ruby runtime doesn't support #bit_length

Also, backports gem need require => false in Gemfile so *all* backports
don't get loaded which we don't want. That is why I had to also bring in
Range#bsearch manually. So now we are not using the backports gem at all.

lib/backports/bit_length.rb

@@ -0,0 +1,86 @@
+# Backport support for Bignum#bit_length and Fixnum#bit_length which were added in Ruby 2.1
+# See : http://globaldev.co.uk/2014/05/ruby-2-1-in-detail/
+# See : https://github.com/marcandre/backports
+#
+# NOTE: Had to add this as a monkey patch here since Bignum#bit_length is broken
+# in the backports gem. Bug filed:
+# https://github.com/marcandre/backports/issues/95
+
+# Supports #bit_length
+# a direct copy from backports gem
+unless Range.method_defined? :bsearch
+  class Range
+    def bsearch
+      return to_enum(:bsearch) unless block_given?
+      from = self.begin
+      to   = self.end
+      unless from.is_a?(Numeric) && to.is_a?(Numeric)
+        raise TypeError, "can't do binary search for #{from.class}"
+      end
+
+      midpoint = nil
+      if from.is_a?(Integer) && to.is_a?(Integer)
+        convert = Proc.new{ midpoint }
+      else
+        map = Proc.new do |pk, unpk, nb|
+          result, = [nb.abs].pack(pk).unpack(unpk)
+          nb < 0 ? -result : result
+        end
+        from = map['D', 'q', to.to_f]
+        to   = map['D', 'q', to.to_f]
+        convert = Proc.new{ map['q', 'D', midpoint] }
+      end
+      to -= 1 if exclude_end?
+      satisfied = nil
+      while from <= to do
+        midpoint = (from + to).div(2)
+        result = yield(cur = convert.call)
+        case result
+        when Numeric
+          return cur if result == 0
+          result = result < 0
+        when true
+          satisfied = cur
+        when nil, false
+          # nothing to do
+        else
+          raise TypeError, "wrong argument type #{result.class} (must be numeric, true, false or nil)"
+        end
+
+        if result
+          to = midpoint - 1
+        else
+          from = midpoint + 1
+        end
+      end
+      satisfied
+    end
+  end
+end
+
+# For MRI < 2.1, and other Rubies
+# A direct copy from backports gem
+unless Fixnum.method_defined? :bit_length
+  # require 'backports/2.0.0/range/bsearch'
+  class Fixnum
+    def bit_length
+      n = if self >= 0
+        self + 1
+      else
+        -self
+      end
+      (0...8 * size).bsearch{|i| n <= (1 << i) }
+    end
+  end
+end
+
+# For MRI < 2.1, and other Rubies
+# My own temporary implementation of bit_length. Until the bug report
+# above is resolved.
+unless Bignum.method_defined? :bit_length
+  class Bignum
+    def bit_length
+      (self).abs.to_s(2).length
+    end
+  end
+end

lib/secretsharing.rb

@@ -14,12 +14,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-# Backport support for Bignum#bit_length and Fixnum#bit_length which were added in Ruby 2.1
-# See : http://globaldev.co.uk/2014/05/ruby-2-1-in-detail/
-# See : https://github.com/marcandre/backports
-require 'backports/1.9.1/kernel/require_relative'
-require 'backports/2.1.0/bignum/bit_length'
-require 'backports/2.1.0/fixnum/bit_length'
+# custom local monkey-patches
+require 'backports/bit_length'
 
 require 'rbnacl/libsodium'
 require 'rbnacl'

secretsharing.gemspec

@@ -28,7 +28,6 @@ Gem::Specification.new do |s|
   s.add_dependency 'rbnacl', '~> 3.2.0'
   s.add_dependency 'highline', '~> 1.7.2'
   s.add_dependency 'multi_json', '~> 1.11.2'
-  s.add_dependency 'backports', '~> 3.6.4'
 
   s.add_development_dependency 'mocha'
   s.add_development_dependency 'minitest'

spec/backport_bit_length_spec.rb

@@ -0,0 +1,57 @@
+# -*- encoding: utf-8 -*-
+
+# Copyright 2011-2015 Glenn Rempe
+
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+
+#     http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+require File.expand_path('../spec_helper', __FILE__)
+
+# NOTE : these backport tests are only meaninful when run on
+# a Ruby runtime that doesn't natively support Bignum.bit_length
+describe 'Bignum#bit_length' do
+  include SecretSharing::Shamir
+
+  it 'will return the expected bit_length for multiples of 256' do
+    [256, 512, 768, 1024].each do |i|
+      r = get_random_number_with_bitlength(i)
+      r.bit_length.must_equal(i)
+    end
+  end
+
+  it 'will return the expected bit_length for multiples of 256 + 1' do
+    [257, 513, 769, 1025].each do |i|
+      r = get_random_number_with_bitlength(i)
+      r.bit_length.must_equal(i)
+    end
+  end
+end
+
+# NOTE : these backport tests are only meaninful when run on
+# a Ruby runtime that doesn't natively support Fixnum.bit_length
+describe 'Fixnum#bit_length' do
+  include SecretSharing::Shamir
+
+  it 'will return the expected bit_length for multiples of 8' do
+    [1, 8, 16, 24, 32].each do |i|
+      r = get_random_number_with_bitlength(i)
+      r.bit_length.must_equal(i)
+    end
+  end
+
+  it 'will return the expected bit_length for multiples of 8 + 1' do
+    [2, 9, 17, 25, 33].each do |i|
+      r = get_random_number_with_bitlength(i)
+      r.bit_length.must_equal(i)
+    end
+  end
+end