Compute String#hash from bytes, not chars

src/pointer.cr

@@ -60,8 +60,14 @@ class Pointer(T)
     self[i], self[j] = self[j], self[i]
   end
 
-  def map(times, &block : T -> U)
-    Array(U).new(times) { |i| yield self[i] }
+  def each(count)
+    count.times do |i|
+      yield self[i]
+    end
+  end
+
+  def map(count, &block : T -> U)
+    Array(U).new(count) { |i| yield self[i] }
   end
 
   def to_a(length)

src/string.cr

@@ -505,6 +505,12 @@ class String
     end
   end
 
+  def each_byte
+    cstr.each(length) do |byte|
+      yield byte
+    end
+  end
+
   def inspect
     "\"#{dump}\""
   end
@@ -562,8 +568,8 @@ class String
 
   def hash
     h = 0
-    each_char do |c|
-      h = 31 * h + c.ord
+    each_byte do |c|
+      h = 31 * h + c
     end
     h
   end