Fix Int#downto with unsigned int going down to 0.

spec/std/int_spec.cr

@@ -454,6 +454,17 @@ describe "Int" do
     sum.should eq(6)
   end
 
+  it "does upto max" do
+    i = sum = 0
+    (Int32::MAX - 3).upto(Int32::MAX) do |n|
+      i += 1
+      sum += Int32::MAX - n
+      n.should be >= (Int32::MAX - 3)
+    end.should be_nil
+    i.should eq(4)
+    sum.should eq(6)
+  end
+
   it "gets upto iterator" do
     iter = 1.upto(3)
     iter.next.should eq(1)
@@ -465,6 +476,26 @@ describe "Int" do
     iter.next.should eq(1)
   end
 
+  it "gets upto iterator max" do
+    iter = (Int32::MAX - 3).upto(Int32::MAX)
+    iter.next.should eq(Int32::MAX - 3)
+    iter.next.should eq(Int32::MAX - 2)
+    iter.next.should eq(Int32::MAX - 1)
+    iter.next.should eq(Int32::MAX)
+    iter.next.should be_a(Iterator::Stop)
+
+    iter.rewind
+    iter.next.should eq(Int32::MAX - 3)
+  end
+
+  it "upto iterator ups and downs" do
+    0.upto(3).to_a.should eq([0, 1, 2, 3])
+    3.upto(0).to_a.should eq([] of Int32)
+    res = [Int32::MAX - 3, Int32::MAX - 2, Int32::MAX - 1, Int32::MAX]
+    (Int32::MAX - 3).upto(Int32::MAX).to_a.should eq(res)
+    Int32::MAX.upto(0).to_a.should eq([] of Int32)
+  end
+
   it "does downto" do
     i = sum = 0
     3.downto(1) do |n|
@@ -475,6 +506,28 @@ describe "Int" do
     sum.should eq(6)
   end
 
+  it "does downto min" do
+    i = sum = 0
+    (Int32::MIN + 3).downto(Int32::MIN) do |n|
+      i += 1
+      sum += n - Int32::MIN
+      n.should be <= Int32::MIN + 3
+    end
+    i.should eq(4)
+    sum.should eq(6)
+  end
+
+  it "does downto min unsigned" do
+    i = sum = 0
+    3_u16.downto(0) do |n|
+      i += 1
+      sum += n
+      n.should be <= 3_u16
+    end
+    i.should eq(4)
+    sum.should eq(6)
+  end
+
   it "gets downto iterator" do
     iter = 3.downto(1)
     iter.next.should eq(3)
@@ -486,6 +539,27 @@ describe "Int" do
     iter.next.should eq(3)
   end
 
+  it "downto iterator ups and downs" do
+    3.downto(0).to_a.should eq([3, 2, 1, 0])
+    3_u16.downto(0).to_a.should eq([3_u16, 2_u16, 1_u16, 0_u16])
+    3.downto(4).to_a.should eq([] of Int32)
+    3_u16.downto(4_u16).to_a.should eq([] of UInt16)
+    res = [Int32::MIN + 3, Int32::MIN + 2, Int32::MIN + 1, Int32::MIN]
+    (Int32::MIN + 3).downto(Int32::MIN).to_a.should eq(res)
+  end
+
+  it "gets downto iterator unsigned" do
+    iter = 3_u16.downto(0)
+    iter.next.should eq(3)
+    iter.next.should eq(2)
+    iter.next.should eq(1)
+    iter.next.should eq(0)
+    iter.next.should be_a(Iterator::Stop)
+
+    iter.rewind
+    iter.next.should eq(3)
+  end
+
   it "gets to iterator" do
     iter = 1.to(3)
     iter.next.should eq(1)

src/int.cr

@@ -353,9 +353,11 @@ struct Int
   end
 
   def upto(to, &block : self ->) : Nil
+    return unless self <= to
     x = self
-    while x <= to
+    while true
       yield x
+      return if x == to
       x += 1
     end
   end
@@ -365,9 +367,11 @@ struct Int
   end
 
   def downto(to, &block : self ->) : Nil
+    return unless self >= to
     x = self
-    while x >= to
+    while true
       yield x
+      return if x == to
       x -= 1
     end
   end
@@ -539,23 +543,24 @@ struct Int
     @from : T
     @to : N
     @current : T
+    @done : Bool
 
     def initialize(@from : T, @to : N)
       @current = @from
+      @done = !(@from <= @to)
     end
 
     def next
-      if @current > @to
-        stop
-      else
-        value = @current
-        @current += 1
-        value
-      end
+      return stop if @done
+      value = @current
+      @done = @current == @to
+      @current += 1 unless @done
+      value
     end
 
     def rewind
       @current = @from
+      @done = !(@from <= @to)
       self
     end
   end
@@ -566,23 +571,24 @@ struct Int
     @from : T
     @to : N
     @current : T
+    @done : Bool
 
     def initialize(@from : T, @to : N)
       @current = @from
+      @done = !(@from >= @to)
     end
 
     def next
-      if @current < @to
-        stop
-      else
-        value = @current
-        @current -= 1
-        value
-      end
+      return stop if @done
+      value = @current
+      @done = @current == @to
+      @current -= 1 unless @done
+      value
     end
 
     def rewind
       @current = @from
+      @done = !(@from >= @to)
       self
     end
   end