String: always compute codepoints size when ascii optimization is ava…

…ilable This only implies a first very small slowdown for computing the size, but after that methods that deal with ASCII-only strings should execute much faster. As a comparison, for this code: ``` # Build a String at runtime so its size is not known at compile-time str = String.build do |str| 50000.times { str << "abc" } str << 'x' end time = Time.now a = 0 100_000.times do a += str[150000].ord end puts a puts Time.now - time ``` Time before: 13.72s. Time after: 0.0008s. This could have a huge impact on code that does string indexing and slicing over a same string that's known to be ASCII only (for example URIs)
crystal-lang · Jul 14, 2016 · f6874e1 · f6874e1
1 parent 351fe7f
commit f6874e1
Showing 1 changed file with 15 additions and 19 deletions.
diff --git a/src/string.cr b/src/string.cr
@@ -647,7 +647,7 @@ class String
   #
   # Raises `ArgumentError` if `count` is negative.
   def [](start : Int, count : Int)
-    if single_byte_optimizable?
+    if ascii_only?
       return byte_slice(start, count)
     end
 
@@ -728,7 +728,7 @@ class String
   end
 
   def at(index : Int)
-    if single_byte_optimizable?
+    if ascii_only?
       byte = byte_at?(index)
       return byte ? byte.unsafe_chr : yield
     end
@@ -746,7 +746,7 @@ class String
 
   def byte_slice(start : Int, count : Int)
     start += bytesize if start < 0
-    single_byte_optimizable = single_byte_optimizable?
+    single_byte_optimizable = ascii_only?
 
     if 0 <= start < bytesize
       raise ArgumentError.new "negative count" if count < 0
@@ -929,7 +929,7 @@ class String
       return byte_slice(0, bytesize - 2)
     end
 
-    if to_unsafe[bytesize - 1] < 128 || single_byte_optimizable?
+    if to_unsafe[bytesize - 1] < 128 || ascii_only?
       return byte_slice(0, bytesize - 1)
     end
 
@@ -999,7 +999,7 @@ class String
     bytes, count = String.char_bytes_and_bytesize(other)
 
     new_bytesize = bytesize + count
-    new_size = single_byte_optimizable? ? new_bytesize : 0
+    new_size = ascii_only? ? new_bytesize : 0
 
     insert_impl(byte_index, bytes.to_unsafe, count, new_bytesize, new_size)
   end
@@ -1028,7 +1028,7 @@ class String
     raise IndexError.new unless byte_index
 
     new_bytesize = bytesize + other.bytesize
-    new_size = single_byte_optimizable? && other.single_byte_optimizable? ? new_bytesize : 0
+    new_size = ascii_only? && other.ascii_only? ? new_bytesize : 0
 
     insert_impl(byte_index, other.to_unsafe, other.bytesize, new_bytesize, new_size)
   end
@@ -1418,7 +1418,7 @@ class String
         buffer.value = byte
         buffer += 1
       end
-      {buffer, single_byte_optimizable? ? bytesize - (to_index - from_index) + 1 : 0}
+      {buffer, ascii_only? ? bytesize - (to_index - from_index) + 1 : 0}
     end
   end
 
@@ -2131,7 +2131,7 @@ class String
   # "こんにちは".char_index_to_byte_index(5) # => 15
   # ```
   def char_index_to_byte_index(index)
-    if single_byte_optimizable?
+    if ascii_only?
       return 0 <= index <= bytesize ? index : nil
     end
 
@@ -2147,7 +2147,7 @@ class String
   # It is valid to pass `bytesize` to *index*, and in this case the answer
   # will be the size of this string.
   def byte_index_to_char_index(index)
-    if single_byte_optimizable?
+    if ascii_only?
       return 0 <= index <= bytesize ? index : nil
     end
 
@@ -2188,7 +2188,7 @@ class String
     end
 
     ary = Array(String).new
-    single_byte_optimizable = single_byte_optimizable?
+    single_byte_optimizable = ascii_only?
     index = 0
     i = 0
     looking_for_space = false
@@ -2250,7 +2250,7 @@ class String
     ary = Array(String).new
 
     byte_offset = 0
-    single_byte_optimizable = single_byte_optimizable?
+    single_byte_optimizable = ascii_only?
 
     reader = Char::Reader.new(self)
     reader.each_with_index do |char, i|
@@ -2296,7 +2296,7 @@ class String
     byte_offset = 0
     separator_bytesize = separator.bytesize
 
-    single_byte_optimizable = single_byte_optimizable?
+    single_byte_optimizable = ascii_only?
 
     i = 0
     stop = bytesize - separator.bytesize + 1
@@ -2724,7 +2724,7 @@ class String
   # end
   # ```
   def each_char
-    if single_byte_optimizable?
+    if ascii_only?
       each_byte do |byte|
         yield byte.unsafe_chr
       end
@@ -2976,7 +2976,7 @@ class String
   def ends_with?(char : Char)
     return false unless bytesize > 0
 
-    if char.ord < 0x80 || single_byte_optimizable?
+    if char.ord < 0x80 || ascii_only?
       return to_unsafe[bytesize - 1] == char.ord
     end
 
@@ -3025,11 +3025,7 @@ class String
   end
 
   def ascii_only?
-    @bytesize == 0 || size == @bytesize
-  end
-
-  protected def single_byte_optimizable?
-    @bytesize == @length
+    @bytesize == size
   end
 
   protected def size_known?