From 1e0356be9ae3c25920e17a65ab6eefd8677f1967 Mon Sep 17 00:00:00 2001
From: Xin Hu <Xin.A.Hu@intel.com>
Date: Thu, 31 Dec 2015 01:11:38 -0500
Subject: [PATCH] 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
---
 jerry-core/lit/lit-strings.cpp | 47 ++++++++++++++++++++++++----------
 jerry-core/lit/lit-strings.h   |  3 +++
 2 files changed, 37 insertions(+), 13 deletions(-)

diff --git a/jerry-core/lit/lit-strings.cpp b/jerry-core/lit/lit-strings.cpp
index 0392181456..5ac0998bf0 100644
--- a/jerry-core/lit/lit-strings.cpp
+++ b/jerry-core/lit/lit-strings.cpp
@@ -757,6 +757,17 @@ lit_utf8_string_code_unit_at (const lit_utf8_byte_t *utf8_buf_p, /**< utf-8 stri
   return code_unit;
 } /* lit_utf8_string_code_unit_at */
 
+/* CESU-8 number of bytes occupied lookup table */
+#ifndef __LITTLE_ENDIAN
+const __attribute__ ((aligned (CESU_8_TABLE_MEM_ALIGNMENT))) lit_utf8_byte_t table[]
+{
+  1, 1, 1, 1, 1, 1, 1, 1,
+  0, 0, 0, 0,
+  2, 2,
+  3, 0
+};
+#endif
+
 /**
  * Get CESU-8 encoded size of character
  *
@@ -765,19 +776,29 @@ 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));
+
+#ifdef __LITTLE_ENDIAN
+  //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
+  //};
+  //                                  MSB     --->                                LSB
+  // on little endian platform, it is 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;
+#else
+  return table[first_byte >> 4];
+#endif
 } /* lit_get_unicode_char_size_by_utf8_first_byte */
 
 /**
diff --git a/jerry-core/lit/lit-strings.h b/jerry-core/lit/lit-strings.h
index f40ca34506..1fa9d4d8d7 100644
--- a/jerry-core/lit/lit-strings.h
+++ b/jerry-core/lit/lit-strings.h
@@ -157,6 +157,9 @@ lit_string_hash_t lit_utf8_string_calc_hash (const lit_utf8_byte_t *, lit_utf8_s
 lit_string_hash_t lit_utf8_string_hash_combine (lit_string_hash_t, const lit_utf8_byte_t *, lit_utf8_size_t);
 
 /* code unit access */
+#ifndef __LITTLE_ENDIAN
+#define  CESU_8_TABLE_MEM_ALIGNMENT  16
+#endif
 ecma_char_t lit_utf8_string_code_unit_at (const lit_utf8_byte_t *, lit_utf8_size_t, ecma_length_t);
 lit_utf8_size_t lit_get_unicode_char_size_by_utf8_first_byte (lit_utf8_byte_t);