Move all utf8 decoding under fx_string.h

Put encoder in cfx_utf8encoder.{h,cpp} to parallel decoder.
Add tests, and fix one corner case involving 0xff.

Change-Id: Ib97540afdc708bcc6280a79c76734ec68ea72690
Reviewed-on: https://pdfium-review.googlesource.com/39770
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>

1 files changed, 43 insertions, 0 deletions

diff --git a/core/fxcrt/cfx_utf8encoder.cpp b/core/fxcrt/cfx_utf8encoder.cpp
new file mode 100644
index 0000000000..9ed149f1ad
--- /dev/null
+++ b/core/fxcrt/cfx_utf8encoder.cpp
@@ -0,0 +1,43 @@
+// Copyright 2018 PDFium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
+
+#include "core/fxcrt/cfx_utf8encoder.h"
+
+CFX_UTF8Encoder::CFX_UTF8Encoder() = default;
+
+CFX_UTF8Encoder::~CFX_UTF8Encoder() = default;
+
+void CFX_UTF8Encoder::Input(wchar_t unicodeAsWchar) {
+  uint32_t unicode = static_cast<uint32_t>(unicodeAsWchar);
+  if (unicode < 0x80) {
+    m_Buffer.push_back(unicode);
+  } else {
+    if (unicode >= 0x80000000)
+      return;
+
+    int nbytes = 0;
+    if (unicode < 0x800)
+      nbytes = 2;
+    else if (unicode < 0x10000)
+      nbytes = 3;
+    else if (unicode < 0x200000)
+      nbytes = 4;
+    else if (unicode < 0x4000000)
+      nbytes = 5;
+    else
+      nbytes = 6;
+
+    static const uint8_t prefix[] = {0xc0, 0xe0, 0xf0, 0xf8, 0xfc};
+    int order = 1 << ((nbytes - 1) * 6);
+    int code = unicodeAsWchar;
+    m_Buffer.push_back(prefix[nbytes - 2] | (code / order));
+    for (int i = 0; i < nbytes - 1; i++) {
+      code = code % order;
+      order >>= 6;
+      m_Buffer.push_back(0x80 | (code / order));
+    }
+  }
+}