Use a statically allocated buffer

Author: vouillon

runtime/wasm/jsstring.wat

@@ -50,6 +50,10 @@
    (global $text_converters_available (mut i32) (i32.const 0))
    (global $string_builtins_available (mut i32) (i32.const 0))
 
+   (global $utf16_buffer_size i32 (i32.const 32768))
+   (global $buffer (mut (ref $wstring))
+      (array.new $wstring (i32.const 0) (i32.const 0)))
+
    (start $init)
 
    (func $init
@@ -74,7 +78,14 @@
                   (i32.const 0) (i32.const 1))
                (call $fromCharCodeArray
                   (array.new_fixed $wstring 1 (i32.const 1))
-                   (i32.const 0) (i32.const 1))))))
+                   (i32.const 0) (i32.const 1)))))
+      (if (i32.eqz (global.get $text_converters_available))
+         (then
+            (if (global.get $string_builtins_available)
+               (then
+                  (global.set $buffer
+                     (array.new $wstring (i32.const 0)
+                        (global.get $utf16_buffer_size))))))))
 
    (func (export "jsstring_compare")
       (param $s anyref) (param $s' anyref) (result i32)
@@ -87,47 +98,37 @@
 
    (export "jsstring_hash" (func $hash_string))
 
-   (func $is_ascii
-      (param $s (ref $string)) (param $i i32) (param $end i32) (result i32)
-      (loop $loop
-         (if (i32.eq (local.get $i) (local.get $end))
-            (then (return (i32.const 1))))
-         (if (i32.gt_u (array.get_u $string (local.get $s) (local.get $i))
-                (i32.const 127))
-            (then (return (i32.const 0))))
-         (local.set $i (i32.add (local.get $i) (i32.const 1)))
-         (br $loop)))
-
    ;; Used by package zarith_stubs_js
    (func $jsstring_of_substring (export "jsstring_of_substring")
       (param $s (ref $string)) (param $pos i32) (param $len i32)
       (result anyref)
-      (local $i i32) (local $ws (ref $wstring))
+      (local $i i32) (local $c i32)
       (if (global.get $text_converters_available)
          (then
             (return
                (any.convert_extern
                   (call $decodeStringFromUTF8Array (local.get $s)
                      (local.get $pos)
                      (i32.add (local.get $pos) (local.get $len)))))))
-      (if (i32.and (global.get $string_builtins_available)
-             (call $is_ascii
-                (local.get $s) (local.get $pos)
-                (i32.add (local.get $pos) (local.get $len))))
+      (if $continue
+         (i32.and (global.get $string_builtins_available)
+            (i32.le_u (local.get $len) (global.get $utf16_buffer_size)))
          (then
-            (local.set $ws (array.new $wstring (i32.const 0) (local.get $len)))
             (loop $loop
                (if (i32.lt_u (local.get $i) (local.get $len))
                   (then
-                     (array.set $wstring (local.get $ws) (local.get $i)
+                     (local.set $c
                         (array.get $string (local.get $s)
                            (i32.add (local.get $pos) (local.get $i))))
+                     (br_if $continue
+                        (i32.ge_u (local.get $c) (i32.const 128)))
+                     (array.set $wstring (global.get $buffer) (local.get $i)
+                        (local.get $c))
                      (local.set $i (i32.add (local.get $i) (i32.const 1)))
-
                      (br $loop))))
             (return
                (any.convert_extern
-                  (call $fromCharCodeArray (local.get $ws)
+                  (call $fromCharCodeArray (global.get $buffer)
                      (i32.const 0) (local.get $len))))))
       (return_call $jsstring_of_substring_fallback
          (local.get $s) (local.get $pos) (local.get $len)))