From 6e2521830f255c6b35ac302363a241274a336c1c Mon Sep 17 00:00:00 2001
From: "arseny.kapoulkine"
 <arseny.kapoulkine@99668b35-9821-0410-8761-19e4c4f06640>
Date: Tue, 25 May 2010 16:50:03 +0000
Subject: [PATCH] Optimized utf8 decoding

git-svn-id: http://pugixml.googlecode.com/svn/trunk@447 99668b35-9821-0410-8761-19e4c4f06640
---
 src/pugixml.cpp | 29 +++++++++++++++++++++++------
 1 file changed, 23 insertions(+), 6 deletions(-)

diff --git a/src/pugixml.cpp b/src/pugixml.cpp
index d404652..bf5253f 100644
--- a/src/pugixml.cpp
+++ b/src/pugixml.cpp
@@ -796,9 +796,7 @@ namespace pugi
 		{
 			const char8_t utf8_byte_mask = 0x3f;
 
-			const char8_t* end = data + size;
-
-			while (data < end)
+			while (size)
 			{
 				char8_t lead = *data;
 
@@ -807,29 +805,48 @@ namespace pugi
 				{
 					result = Traits::low(result, lead);
 					data += 1;
+					size -= 1;
+
+					// process aligned single-byte (ascii) blocks
+					if ((reinterpret_cast<uintptr_t>(data) & 3) == 0)
+					{
+						while (size >= 4 && (*reinterpret_cast<const char32_t*>(data) & 0x80808080) == 0)
+						{
+							result = Traits::low(result, data[0]);
+							result = Traits::low(result, data[1]);
+							result = Traits::low(result, data[2]);
+							result = Traits::low(result, data[3]);
+							data += 4;
+							size -= 4;
+						}
+					}
 				}
 				// 110xxxxx -> U+0080..U+07FF
-				else if ((unsigned)(lead - 0xC0) < 0x20 && (end - data) > 1 && (data[1] & 0xc0) == 0x80)
+				else if ((unsigned)(lead - 0xC0) < 0x20 && size >= 2 && (data[1] & 0xc0) == 0x80)
 				{
 					result = Traits::low(result, ((lead & ~0xC0) << 6) | (data[1] & utf8_byte_mask));
 					data += 2;
+					size -= 2;
 				}
 				// 1110xxxx -> U+0800-U+FFFF
-				else if ((unsigned)(lead - 0xE0) < 0x10 && (end - data) > 2 && (data[1] & 0xc0) == 0x80 && (data[2] & 0xc0) == 0x80)
+				else if ((unsigned)(lead - 0xE0) < 0x10 && size >= 3 && (data[1] & 0xc0) == 0x80 && (data[2] & 0xc0) == 0x80)
 				{
 					result = Traits::low(result, ((lead & ~0xE0) << 12) | ((data[1] & utf8_byte_mask) << 6) | (data[2] & utf8_byte_mask));
 					data += 3;
+					size -= 3;
 				}
 				// 11110xxx -> U+10000..U+10FFFF
-				else if ((unsigned)(lead - 0xF0) < 0x08 && (end - data) > 3 && (data[1] & 0xc0) == 0x80 && (data[2] & 0xc0) == 0x80 && (data[3] & 0xc0) == 0x80)
+				else if ((unsigned)(lead - 0xF0) < 0x08 && size >= 4 && (data[1] & 0xc0) == 0x80 && (data[2] & 0xc0) == 0x80 && (data[3] & 0xc0) == 0x80)
 				{
 					result = Traits::high(result, ((lead & ~0xF0) << 18) | ((data[1] & utf8_byte_mask) << 12) | ((data[2] & utf8_byte_mask) << 6) | (data[3] & utf8_byte_mask));
 					data += 4;
+					size -= 4;
 				}
 				// 10xxxxxx or 11111xxx -> invalid
 				else
 				{
 					data += 1;
+					size -= 1;
 				}
 			}