Fix float number overflow in range rand method

spec/std/random_spec.cr

@@ -131,24 +131,42 @@ describe "Random" do
 
   it "does with inclusive range of floats" do
     rand(1.0..1.0).should eq(1.0)
+
     x = rand(1.8..3.2)
     x.should be >= 1.8
     x.should be <= 3.2
 
+    x = rand(Float64::MIN..Float64::MAX)
+    x.should be >= Float64::MIN
+    x.should be <= Float64::MAX
+
     rand(1.0_f32..1.0_f32).should eq(1.0_f32)
+
     x = rand(1.8_f32..3.2_f32)
     x.should be >= 1.8_f32
     x.should be <= 3.2_f32
+
+    x = rand(Float32::MIN..Float32::MAX)
+    x.should be >= Float32::MIN
+    x.should be <= Float32::MAX
   end
 
   it "does with exclusive range of floats" do
     x = rand(1.8...3.3)
     x.should be >= 1.8
     x.should be < 3.3
 
+    x = rand(Float64::MIN...Float64::MAX)
+    x.should be >= Float64::MIN
+    x.should be < Float64::MAX
+
     x = rand(1.8_f32...3.3_f32)
     x.should be >= 1.8_f32
     x.should be < 3.3_f32
+
+    x = rand(Float32::MIN...Float32::MAX)
+    x.should be >= Float32::MIN
+    x.should be < Float32::MAX
   end
 
   describe "raises on invalid range" do
@@ -178,6 +196,30 @@ describe "Random" do
         rand(1.0..0.0)
       end
     end
+
+    it "infinite range" do
+      expect_raises ArgumentError, "Invalid range for rand: 0.0..Infinity" do
+        rand(0.0..Float64::INFINITY)
+      end
+      expect_raises ArgumentError, "Invalid range for rand: -Infinity..0.0" do
+        rand(-Float64::INFINITY..0.0)
+      end
+      expect_raises ArgumentError, "Invalid range for rand: -Infinity..Infinity" do
+        rand(-Float64::INFINITY..Float64::INFINITY)
+      end
+    end
+
+    it "nan range" do
+      expect_raises ArgumentError, "Invalid range for rand: 0.0..NaN" do
+        rand(0.0..Float64::NAN)
+      end
+      expect_raises ArgumentError, "Invalid range for rand: NaN..0.0" do
+        rand(Float64::NAN..0.0)
+      end
+      expect_raises ArgumentError, "Invalid range for rand: NaN..NaN" do
+        rand(Float64::NAN..Float64::NAN)
+      end
+    end
   end
 
   it "allows creating a new default random" do

src/big/big_float.cr

@@ -465,6 +465,18 @@ module Math
   end
 end
 
+module Random
+  private def rand_range(range : Range(BigFloat, BigFloat)) : BigFloat
+    span = range.end - range.begin
+    if range.exclusive?
+      return range.begin + span*rand(1.0) if span > 0
+    else
+      return range.begin + span*rand if span >= 0
+    end
+    raise ArgumentError.new "Invalid range for rand: #{range}"
+  end
+end
+
 # :nodoc:
 struct Crystal::Hasher
   def float(value : BigFloat)

src/random.cr

@@ -244,6 +244,25 @@ module Random
     {% end %}
   {% end %}
 
+  {% for size in [32, 64] %}
+    {% type = "Float#{size}".id %}
+    private def rand_range(range : Range({{type}}, {{type}})) : {{type}}
+      half_begin = range.begin / 2
+      half_end = range.end / 2
+      half_span = half_end - half_begin
+
+      if half_span.finite?
+        middle = half_begin + half_end
+        if range.exclusive?
+          return middle + half_span*(2*rand(1.0) - 1) if half_span > 0
+        else
+          return middle + half_span*(2*rand - 1) if half_span >= 0
+        end
+      end
+      raise ArgumentError.new "Invalid range for rand: #{range}"
+    end
+  {% end %}
+
   # Returns a random `Float` which is greater than or equal to `0`
   # and less than *max*.
   #
@@ -286,18 +305,7 @@ module Random
   # Random.new.rand(6.2..21.768) # => 15.2989
   # ```
   def rand(range : Range(Float, Float)) : Float
-    span = range.end - range.begin
-    if range.excludes_end?
-      unless range.begin < range.end
-        raise ArgumentError.new "Invalid range for rand: #{range}"
-      end
-      range.begin + rand(span)
-    else
-      unless range.begin <= range.end
-        raise ArgumentError.new "Invalid range for rand: #{range}"
-      end
-      range.begin + rand * span
-    end
+    rand_range(range)
   end
 
   {% for type, values in {