From 5e1d926053aef5f97f90b0cb7471aaef9ecce297 Mon Sep 17 00:00:00 2001
From: "dcarney@chromium.org"
 <dcarney@chromium.org@ce2b1a6d-e550-0410-aec6-3dcde31c8c00>
Date: Wed, 13 Mar 2013 19:43:45 +0000
Subject: [PATCH] Some Utf8Length microoptimizations

R=yangguo@chromium.org
BUG=

Review URL: https://codereview.chromium.org/12783002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13938 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
---
 src/api.cc        | 71 ++++++++++++++++++++++++++-----------------------------
 src/unicode-inl.h | 12 ++++++++++
 src/unicode.h     |  1 +
 3 files changed, 47 insertions(+), 37 deletions(-)

diff --git a/src/api.cc b/src/api.cc
index 9441810..faba6de 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -4011,31 +4011,30 @@ class Utf8LengthHelper : public i::AllStatic {
 
   class Visitor {
    public:
-    explicit Visitor()
+    inline explicit Visitor()
       : utf8_length_(0),
         state_(kInitialState) {}
 
-    template<typename Char>
-    inline void Visit(const Char* chars, int length) {
+    void VisitOneByteString(const uint8_t* chars, int length) {
       int utf8_length = 0;
-      int last_character = unibrow::Utf16::kNoPreviousCharacter;
+      // Add in length 1 for each non-ASCII character.
       for (int i = 0; i < length; i++) {
-        uint16_t c = chars[i];
-        utf8_length += unibrow::Utf8::Length(c, last_character);
-        if (sizeof(Char) > 1) {
-          last_character = c;
-        }
+        utf8_length += *chars++ >> 7;
       }
-      utf8_length_ = utf8_length;
-    }
-
-    void VisitOneByteString(const uint8_t* chars, int length) {
-      Visit(chars, length);
+      // Add in length 1 for each character.
+      utf8_length_ = utf8_length + length;
       state_ = kInitialState;
     }
 
     void VisitTwoByteString(const uint16_t* chars, int length) {
-      Visit(chars, length);
+      int utf8_length = 0;
+      int last_character = unibrow::Utf16::kNoPreviousCharacter;
+      for (int i = 0; i < length; i++) {
+        uint16_t c = chars[i];
+        utf8_length += unibrow::Utf8::Length(c, last_character);
+        last_character = c;
+      }
+      utf8_length_ = utf8_length;
       uint8_t state = 0;
       if (unibrow::Utf16::IsTrailSurrogate(chars[0])) {
         state |= kStartsWithTrailingSurrogate;
@@ -4132,32 +4131,30 @@ class Utf8LengthHelper : public i::AllStatic {
       if (right_as_cons == NULL) {
         total_length += leaf_length;
         MergeLeafRight(&total_length, &state, right_leaf_state);
-        // Terminal node.
-        if (left_as_cons == NULL) {
-          MergeTerminal(&total_length, state, state_out);
-          return total_length;
-        }
-      } else if (left_as_cons != NULL) {
-        // Both strings are ConsStrings.
-        // Recurse on smallest.
-        if (left->length() < right->length()) {
-          total_length += Calculate(left_as_cons, &left_leaf_state);
-          MergeLeafLeft(&total_length, &state, left_leaf_state);
-          current = right_as_cons;
-          continue;
-        } else {
-          total_length += Calculate(right_as_cons, &right_leaf_state);
-          MergeLeafRight(&total_length, &state, right_leaf_state);
+        if (left_as_cons != NULL) {
+          // 1 Leaf node. Descend in place.
           current = left_as_cons;
           continue;
+        } else {
+          // Terminal node.
+          MergeTerminal(&total_length, state, state_out);
+          return total_length;
         }
+      } else if (left_as_cons == NULL) {
+        // 1 Leaf node. Descend in place.
+        current = right_as_cons;
+        continue;
       }
-      // 1 leaf node. Do in place descent.
-      if (left_as_cons != NULL) {
-        current = left_as_cons;
-      } else {
-        ASSERT(right_as_cons != NULL);
+      // Both strings are ConsStrings.
+      // Recurse on smallest.
+      if (left->length() < right->length()) {
+        total_length += Calculate(left_as_cons, &left_leaf_state);
+        MergeLeafLeft(&total_length, &state, left_leaf_state);
         current = right_as_cons;
+      } else {
+        total_length += Calculate(right_as_cons, &right_leaf_state);
+        MergeLeafRight(&total_length, &state, right_leaf_state);
+        current = left_as_cons;
       }
     }
     UNREACHABLE();
@@ -4267,7 +4264,7 @@ class Utf8WriterVisitor {
       if (sizeof(Char) == 1) {
         for (; i < fast_length; i++) {
           buffer +=
-              Utf8::Encode(buffer, *chars++, Utf16::kNoPreviousCharacter);
+              Utf8::EncodeOneByte(buffer, static_cast<uint8_t>(*chars++));
           ASSERT(capacity_ == -1 || (buffer - start_) <= capacity_);
         }
       } else {
diff --git a/src/unicode-inl.h b/src/unicode-inl.h
index c80c67e..02be457 100644
--- a/src/unicode-inl.h
+++ b/src/unicode-inl.h
@@ -95,6 +95,18 @@ uint16_t Latin1::ConvertNonLatin1ToLatin1(uint16_t c) {
 }
 
 
+unsigned Utf8::EncodeOneByte(char* str, uint8_t c) {
+  static const int kMask = ~(1 << 6);
+  if (c <= kMaxOneByteChar) {
+    str[0] = c;
+    return 1;
+  }
+  str[0] = 0xC0 | (c >> 6);
+  str[1] = 0x80 | (c & kMask);
+  return 2;
+}
+
+
 unsigned Utf8::Encode(char* str, uchar c, int previous) {
   static const int kMask = ~(1 << 6);
   if (c <= kMaxOneByteChar) {
diff --git a/src/unicode.h b/src/unicode.h
index f8a1f60..3279ad8 100644
--- a/src/unicode.h
+++ b/src/unicode.h
@@ -149,6 +149,7 @@ class Latin1 {
 class Utf8 {
  public:
   static inline uchar Length(uchar chr, int previous);
+  static inline unsigned EncodeOneByte(char* out, uint8_t c);
   static inline unsigned Encode(
       char* out, uchar c, int previous);
   static uchar CalculateValue(const byte* str,
-- 
2.7.4