From 4d36ecc2295117c77750e0c1df71cb65362549c5 Mon Sep 17 00:00:00 2001
From: Zufu Liu <unknown>
Date: Fri, 12 Apr 2019 08:22:21 +1000
Subject: Backport: Bug [#2093]. Improve efficiency with single byte character
 sets.

Backport of changeset 7424:0d4b29e058f7.
---
 src/DBCS.h        | 8 ++++++++
 win32/PlatWin.cxx | 4 ++--
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/DBCS.h b/src/DBCS.h
index ff3f9f22f..58659ee3e 100644
--- a/src/DBCS.h
+++ b/src/DBCS.h
@@ -10,6 +10,14 @@
 
 namespace Scintilla {
 
+constexpr bool IsDBCSCodePage(int codePage) noexcept {
+	return codePage == 932
+	       || codePage == 936
+	       || codePage == 949
+	       || codePage == 950
+	       || codePage == 1361;
+}
+
 bool DBCSIsLeadByte(int codePage, char ch) noexcept;
 
 }
diff --git a/win32/PlatWin.cxx b/win32/PlatWin.cxx
index 4ccc40f14..2b807198a 100644
--- a/win32/PlatWin.cxx
+++ b/win32/PlatWin.cxx
@@ -1177,7 +1177,7 @@ void SurfaceD2D::SetFont(Font &font_) {
 	yDescent = pfm->yDescent;
 	yInternalLeading = pfm->yInternalLeading;
 	codePageText = codePage;
-	if (pfm->characterSet) {
+	if (!unicodeMode && pfm->characterSet) {
 		codePageText = Scintilla::CodePageFromCharSet(pfm->characterSet, codePage);
 	}
 	if (pRenderTarget) {
@@ -1613,7 +1613,7 @@ void SurfaceD2D::MeasureWidths(Font &font_, const char *s, int len, XYPOSITION *
 		while (i<len) {
 			positions[i++] = lastPos;
 		}
-	} else if (codePageText == 0) {
+	} else if (!IsDBCSCodePage(codePageText)) {
 
 		// One char per position
 		PLATFORM_ASSERT(len == tbuf.tlen);
-- 
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