Port Float#next_float & Float#prev_float

Somehow rubyspec/rubyspec#297 didn't made it into rubinius. Ported over @jemc pr into rubinius.
rubinius · May 26, 2015 · 952991e · 952991e
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diff --git a/spec/ruby/core/float/next_float_spec.rb b/spec/ruby/core/float/next_float_spec.rb
@@ -0,0 +1,44 @@
+require File.expand_path('../../../spec_helper', __FILE__)
+
+describe "Float" do
+  it "returns a float the smallest possible step greater than the receiver" do
+    barely_positive = 0.0.next_float
+    barely_positive.should eql 0.0.next_float
+
+    barely_positive.should > 0.0
+    barely_positive.should < barely_positive.next_float
+
+    midpoint = barely_positive / 2
+    [0.0, barely_positive].should include midpoint
+  end
+
+  it "steps directly between MAX and INFINITY" do
+    (-Float::INFINITY).next_float.should eql -Float::MAX
+    Float::MAX.next_float.should eql Float::INFINITY
+  end
+
+  it "steps directly between 1.0 and EPSILON + 1.0" do
+    1.0.next_float.should eql Float::EPSILON + 1.0
+  end
+
+  it "steps directly between -1.0 and EPSILON/2 - 1.0" do
+    (-1.0).next_float.should eql Float::EPSILON/2 - 1.0
+  end
+
+  it "reverses the effect of prev_float" do
+    num = rand
+    num.prev_float.next_float.should eql num
+  end
+
+  it "returns negative zero when stepping upward from just below zero" do
+    x = 0.0.prev_float.next_float
+    (1/x).should eql -Float::INFINITY
+    x = (-0.0).prev_float.next_float
+    (1/x).should eql -Float::INFINITY
+    x.next_float.should > 0
+  end
+
+  it "returns NAN if NAN was the receiver" do
+    Float::NAN.next_float.nan?.should eql true
+  end
+end
diff --git a/spec/ruby/core/float/prev_float_spec.rb b/spec/ruby/core/float/prev_float_spec.rb
@@ -0,0 +1,44 @@
+require File.expand_path('../../../spec_helper', __FILE__)
+
+describe "Float" do
+  it "returns a float the smallest possible step greater than the receiver" do
+    barely_negative = 0.0.prev_float
+    barely_negative.should eql 0.0.prev_float
+
+    barely_negative.should < 0.0
+    barely_negative.should > barely_negative.prev_float
+
+    midpoint = barely_negative / 2
+    [0.0, barely_negative].should include midpoint
+  end
+
+  it "steps directly between MAX and INFINITY" do
+    Float::INFINITY.prev_float.should eql Float::MAX
+    (-Float::MAX).prev_float.should eql -Float::INFINITY
+  end
+
+  it "steps directly between 1.0 and -EPSILON/2 + 1.0" do
+    1.0.prev_float.should eql -Float::EPSILON/2 + 1.0
+  end
+
+  it "steps directly between -1.0 and -EPSILON - 1.0" do
+    (-1.0).prev_float.should eql -Float::EPSILON - 1.0
+  end
+
+  it "reverses the effect of next_float" do
+    num = rand
+    num.next_float.prev_float.should eql num
+  end
+
+  it "returns positive zero when stepping downward from just above zero" do
+    x = 0.0.next_float.prev_float
+    (1/x).should eql Float::INFINITY
+    x = (-0.0).next_float.prev_float
+    (1/x).should eql Float::INFINITY
+    x.prev_float.should < 0
+  end
+
+  it "returns NAN if NAN was the receiver" do
+    Float::NAN.prev_float.nan?.should eql true
+  end
+end
diff --git a/spec/tags/ruby/core/float/next_float_tags.txt b/spec/tags/ruby/core/float/next_float_tags.txt
@@ -0,0 +1,7 @@
+fails:returns a float the smallest possible step greater than the receiver
+fails:steps directly between MAX and INFINITY
+fails:steps directly between 1.0 and EPSILON + 1.0
+fails:steps directly between -1.0 and EPSILON/2 - 1.0
+fails:reverses the effect of prev_float
+fails:returns negative zero when stepping upward from just below zero
+fails:returns NAN if NAN was the receiver
diff --git a/spec/tags/ruby/core/float/prev_float_tags.txt b/spec/tags/ruby/core/float/prev_float_tags.txt
@@ -0,0 +1,7 @@
+fails:returns a float the smallest possible step greater than the receiver
+fails:steps directly between MAX and INFINITY
+fails:steps directly between 1.0 and -EPSILON/2 + 1.0
+fails:steps directly between -1.0 and -EPSILON - 1.0
+fails:reverses the effect of next_float
+fails:returns positive zero when stepping downward from just above zero
+fails:returns NAN if NAN was the receiver