Use faster IsDecimalDigit in the json parser

src/json-parser.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_JSON_PARSER_H_
 #define V8_JSON_PARSER_H_
 
 #include "src/v8.h"
 
 #include "src/char-predicates-inl.h"
@@ skipping 296 matching lines @@
 
   AdvanceSkipWhitespace();
   if (c0_ != '}') {
     do {
       if (c0_ != '"') return ReportUnexpectedCharacter();
 
       int start_position = position_;
       Advance();
 
       uint32_t index = 0;
-      if (c0_ >= '0' && c0_ <= '9') {
+      if (IsDecimalDigit(c0_)) {
         // Maybe an array index, try to parse it.
         if (c0_ == '0') {
           // With a leading zero, the string has to be "0" only to be an index.
           Advance();
         } else {
           do {
             int d = c0_ - '0';
             if (index > 429496729U - ((d > 5) ? 1 : 0)) break;
             index = (index * 10) + d;
             Advance();
-          } while (c0_ >= '0' && c0_ <= '9');
+          } while (IsDecimalDigit(c0_));
         }
 
         if (c0_ == '"') {
           // Successfully parsed index, parse and store element.
           AdvanceSkipWhitespace();
 
           if (c0_ != ':') return ReportUnexpectedCharacter();
           AdvanceSkipWhitespace();
           Handle<Object> value = ParseJsonValue();
           if (value.is_null()) return ReportUnexpectedCharacter();
@@ skipping 169 matching lines @@
   bool negative = false;
   int beg_pos = position_;
   if (c0_ == '-') {
     Advance();
     negative = true;
   }
   if (c0_ == '0') {
     Advance();
     // Prefix zero is only allowed if it's the only digit before
     // a decimal point or exponent.
-    if ('0' <= c0_ && c0_ <= '9') return ReportUnexpectedCharacter();
+    if (IsDecimalDigit(c0_)) return ReportUnexpectedCharacter();
   } else {
     int i = 0;
     int digits = 0;
     if (c0_ < '1' || c0_ > '9') return ReportUnexpectedCharacter();
     do {
       i = i * 10 + c0_ - '0';
       digits++;
       Advance();
-    } while (c0_ >= '0' && c0_ <= '9');
+    } while (IsDecimalDigit(c0_));
     if (c0_ != '.' && c0_ != 'e' && c0_ != 'E' && digits < 10) {
       SkipWhitespace();
       return Handle<Smi>(Smi::FromInt((negative ? -i : i)), isolate());
     }
   }
   if (c0_ == '.') {
     Advance();
-    if (c0_ < '0' || c0_ > '9') return ReportUnexpectedCharacter();
+    if (!IsDecimalDigit(c0_)) return ReportUnexpectedCharacter();
     do {
       Advance();
-    } while (c0_ >= '0' && c0_ <= '9');
+    } while (IsDecimalDigit(c0_));
   }
   if (AsciiAlphaToLower(c0_) == 'e') {
     Advance();
     if (c0_ == '-' || c0_ == '+') Advance();
-    if (c0_ < '0' || c0_ > '9') return ReportUnexpectedCharacter();
+    if (!IsDecimalDigit(c0_)) return ReportUnexpectedCharacter();
     do {
       Advance();
-    } while (c0_ >= '0' && c0_ <= '9');
+    } while (IsDecimalDigit(c0_));
   }
   int length = position_ - beg_pos;
   double number;
   if (seq_one_byte) {
     Vector<const uint8_t> chars(seq_source_->GetChars() +  beg_pos, length);
     number = StringToDouble(isolate()->unicode_cache(), chars,
                             NO_FLAGS,  // Hex, octal or trailing junk.
                             std::numeric_limits<double>::quiet_NaN());
   } else {
     Vector<uint8_t> buffer = Vector<uint8_t>::New(length);
@@ skipping 250 matching lines @@
 
   DCHECK_EQ('"', c0_);
   // Advance past the last '"'.
   AdvanceSkipWhitespace();
   return result;
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_JSON_PARSER_H_