[GR-18163] Fix Random#rand when given a float range not returning random floats

PullRequest: truffleruby/3215

Author: bjfish

CHANGELOG.md

@@ -17,6 +17,7 @@ Bug fixes:
 * Update patch feature finding to prefer the longest matching load path (#2605, @bjfish).
 * Fix `Hash#{to_s,inspect}` for keys whose `#inspect` return a frozen String (#2613, @eregon).
 * Fix `Array#pack` with `x*` to not output null characters (#2614, @bjfish).
+* Fix `Random#rand` not returning random floats when given float ranges (#2612, @bjfish).
 
 Compatibility:
 

spec/ruby/core/random/rand_spec.rb

@@ -205,6 +205,11 @@
     Random.new(42).rand(0..1.0).should be_kind_of(Float)
   end
 
+  it "returns a float within a given float range" do
+    Random.new(42).rand(0.0...100.0).should == 37.454011884736246
+    Random.new(42).rand(-100.0...0.0).should == -62.545988115263754
+  end
+
   it "raises an ArgumentError when the startpoint lacks #+ and #- methods" do
     -> do
       Random.new.rand(Object.new..67)

src/main/ruby/truffleruby/core/truffle/random_operations.rb

@@ -89,8 +89,8 @@ def self.rand_range(randomizer, range)
         end
 
         if max > 0.0
+          r = randomizer.random_float
           if scale > 1
-            r = randomizer.random_float
             r *= 1.0000000000000002 unless exclude_end
             return +(+(+(r - 0.5) * max) * scale) + mid
           end