Rewrite IsHyphen using string operations

The existing code did end of range checks by making sure that the 
value was never less then 0. This isn't correct when using an unsigned
type, since 0 - 1 will wrap around to the max possible value, and
thus still be less then 0. Additionally the existing code was hard to
follow due to the complexity of some of the low level operations being 
performed.

It has been rewritten using higher level string operations to make it
clearer and correct.

BUG=chromium:763256

Change-Id: Ib8bf5ca0e29e73724c4a1c4781362e8a8fc30149
Reviewed-on: https://pdfium-review.googlesource.com/13690
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>

2 files changed, 35 insertions, 30 deletions

diff --git a/core/fpdftext/cpdf_textpage.cpp b/core/fpdftext/cpdf_textpage.cpp
index 3006ebce2b..ee1d51bfd8 100644
--- a/core/fpdftext/cpdf_textpage.cpp
+++ b/core/fpdftext/cpdf_textpage.cpp
@@ -106,6 +106,10 @@ float MaskPercentFilled(const std::vector<bool>& mask,
   return count / (end - start);
 }
 
+bool IsHyphenCode(wchar_t c) {
+  return c == 0x2D || c == 0xAD;
+}
+
 }  // namespace
 
 PDFTEXT_Obj::PDFTEXT_Obj() {}
@@ -1215,36 +1219,37 @@ CPDF_TextPage::TextOrientation CPDF_TextPage::GetTextObjectWritingMode(
   return m_TextlineDir;
 }
 
-bool CPDF_TextPage::IsHyphen(wchar_t curChar) {
-  CFX_WideString strCurText = m_TempTextBuf.MakeString();
-  if (strCurText.IsEmpty())
-    strCurText = m_TextBuf.AsStringC();
-  FX_STRSIZE nCount = strCurText.GetLength();
-  if (nCount < 1)
+bool CPDF_TextPage::IsHyphen(wchar_t curChar) const {
+  CFX_WideStringC curText;
+  if (!m_TempTextBuf.IsEmpty())
+    curText = m_TempTextBuf.AsStringC();
+  else if (!m_TextBuf.IsEmpty())
+    curText = m_TextBuf.AsStringC();
+  else
     return false;
-  FX_STRSIZE nIndex = nCount - 1;
-  wchar_t wcTmp = strCurText[nIndex];
-  while (wcTmp == 0x20 && nIndex > 0 && nIndex <= nCount - 1)
-    wcTmp = strCurText[--nIndex];
-  if (0x2D == wcTmp || 0xAD == wcTmp) {
-    if (--nIndex > 0) {
-      wchar_t preChar = strCurText[nIndex];
-      if (FXSYS_iswalpha(preChar) && FXSYS_iswalpha(curChar))
-        return true;
-    }
-    const PAGECHAR_INFO* preInfo;
-    if (!m_TempCharList.empty())
-      preInfo = &m_TempCharList.back();
-    else if (!m_CharList.empty())
-      preInfo = &m_CharList.back();
-    else
-      return false;
-    if (FPDFTEXT_CHAR_PIECE == preInfo->m_Flag &&
-        (0xAD == preInfo->m_Unicode || 0x2D == preInfo->m_Unicode)) {
-      return true;
-    }
-  }
-  return false;
+
+  curText = curText.TrimmedRight(0x20);
+  if (curText.GetLength() < 2)
+    return false;
+
+  // Extracting the last 2 characters, since they are all that matter
+  curText = curText.Right(2);
+  if (!IsHyphenCode(curText.Last()))
+    return false;
+
+  if (FXSYS_iswalpha(curText.First() && FXSYS_iswalnum(curChar)))
+    return true;
+
+  const PAGECHAR_INFO* preInfo;
+  if (!m_TempCharList.empty())
+    preInfo = &m_TempCharList.back();
+  else if (!m_CharList.empty())
+    preInfo = &m_CharList.back();
+  else
+    return false;
+
+  return FPDFTEXT_CHAR_PIECE == preInfo->m_Flag &&
+         IsHyphenCode(preInfo->m_Unicode);
 }
 
 CPDF_TextPage::GenerateCharacter CPDF_TextPage::ProcessInsertObject(
diff --git a/core/fpdftext/cpdf_textpage.h b/core/fpdftext/cpdf_textpage.h
index 6a4c87368d..41892ea97c 100644
--- a/core/fpdftext/cpdf_textpage.h
+++ b/core/fpdftext/cpdf_textpage.h
@@ -132,7 +132,7 @@ class CPDF_TextPage {
     Hyphen,
   };
 
-  bool IsHyphen(wchar_t curChar);
+  bool IsHyphen(wchar_t curChar) const;
   bool IsControlChar(const PAGECHAR_INFO& charInfo);
   void ProcessObject();
   void ProcessFormObject(CPDF_FormObject* pFormObj,