Use bit vector to store CESU-8 lookup table,

to improve lit_get_unicode_char_size_by_utf8_first_byte performance

JerryScript-DCO-1.0-Signed-off-by: Xin Hu Xin.A.Hu@intel.com

Author: huxinx

jerry-core/lit/lit-strings.cpp

@@ -765,19 +765,24 @@ lit_utf8_string_code_unit_at (const lit_utf8_byte_t *utf8_buf_p, /**< utf-8 stri
 lit_utf8_size_t
 lit_get_unicode_char_size_by_utf8_first_byte (const lit_utf8_byte_t first_byte) /**< buffer with characters */
 {
-  if ((first_byte & LIT_UTF8_1_BYTE_MASK) == LIT_UTF8_1_BYTE_MARKER)
-  {
-    return 1;
-  }
-  else if ((first_byte & LIT_UTF8_2_BYTE_MASK) == LIT_UTF8_2_BYTE_MARKER)
-  {
-    return 2;
-  }
-  else
-  {
-    JERRY_ASSERT ((first_byte & LIT_UTF8_3_BYTE_MASK) == LIT_UTF8_3_BYTE_MARKER);
-    return 3;
-  }
+  JERRY_ASSERT (((first_byte >> 4) <= 7 || (first_byte >> 4) == 12 ||
+    (first_byte >> 4) == 13 || (first_byte >> 4) == 14));
+
+  //compact CESU-8 length lookup table into an uint32_t, every two bits represent one item
+  //const lit_utf8_byte_t table[]
+  //{
+  //  1, 1, 1, 1, 1, 1, 1, 1,
+  //  0, 0, 0, 0,
+  //  2, 2,
+  //  3, 0
+  //};
+  //               uint32             00 11 10 10 00 00 00 00 01 01 01 01 01 01 01 01
+  //               table index:       15 14 13 12 11 10  9  8  7  6  5  4  3  2  1  0
+
+  const uint32_t cesu_8_store = 0x3a005555;
+  int shift = (first_byte >> 4) << 1;
+
+  return (cesu_8_store >> shift) & 0x3;
 } /* lit_get_unicode_char_size_by_utf8_first_byte */
 
 /**