Remove GetAt from string classes

This method duplicates the behaviour of the const [] operator and
doesn't offer any additional safety. Folding them into one
implementation.

SetAt is retained, since implementing the non-const [] operator to
replace SetAt has potential performance concerns. Specifically many
non-obvious cases of reading an element using [] will cause a realloc
& copy.

BUG=pdfium:860

Change-Id: I3ef5e5e5a15376f040256b646eb0d90636e24b67
Reviewed-on: https://pdfium-review.googlesource.com/10870
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>

4 files changed, 18 insertions, 19 deletions

diff --git a/core/fpdfapi/font/cpdf_cidfont.cpp b/core/fpdfapi/font/cpdf_cidfont.cpp
index 8cb59de739..9a2261caa9 100644
--- a/core/fpdfapi/font/cpdf_cidfont.cpp
+++ b/core/fpdfapi/font/cpdf_cidfont.cpp
@@ -627,7 +627,7 @@ int CPDF_CIDFont::GlyphFromCharCode(uint32_t charcode, bool* pVertGlyph) {
       if (uni_str.IsEmpty())
         return cid;
 
-      unicode = uni_str.GetAt(0);
+      unicode = uni_str[0];
 #endif
     } else {
       if (cid && m_pCID2UnicodeMap && m_pCID2UnicodeMap->IsLoaded())
@@ -637,7 +637,7 @@ int CPDF_CIDFont::GlyphFromCharCode(uint32_t charcode, bool* pVertGlyph) {
       if (unicode == 0) {
         CFX_WideString unicode_str = UnicodeFromCharCode(charcode);
         if (!unicode_str.IsEmpty())
-          unicode = unicode_str.GetAt(0);
+          unicode = unicode_str[0];
       }
     }
     FXFT_Face face = m_Font.GetFace();
@@ -735,7 +735,7 @@ int CPDF_CIDFont::GlyphFromCharCode(uint32_t charcode, bool* pVertGlyph) {
       if (unicode_str.IsEmpty())
         return -1;
 
-      charcode = unicode_str.GetAt(0);
+      charcode = unicode_str[0];
     }
     return GetGlyphIndex(charcode, pVertGlyph);
   }
diff --git a/core/fpdfapi/font/cpdf_cmapparser.cpp b/core/fpdfapi/font/cpdf_cmapparser.cpp
index cbf693966e..272f8deb34 100644
--- a/core/fpdfapi/font/cpdf_cmapparser.cpp
+++ b/core/fpdfapi/font/cpdf_cmapparser.cpp
@@ -121,7 +121,7 @@ void CPDF_CMapParser::ParseWord(const CFX_ByteStringC& word) {
       }
       m_Status = 0;
     } else {
-      if (word.GetLength() == 0 || word.GetAt(0) != '<') {
+      if (word.GetLength() == 0 || word[0] != '<') {
         return;
       }
       if (m_CodeSeq % 2) {
@@ -140,18 +140,17 @@ uint32_t CPDF_CMapParser::CMap_GetCode(const CFX_ByteStringC& word) {
   if (word.IsEmpty())
     return 0;
   pdfium::base::CheckedNumeric<uint32_t> num = 0;
-  if (word.GetAt(0) == '<') {
-    for (int i = 1; i < word.GetLength() && std::isxdigit(word.GetAt(i)); ++i) {
-      num = num * 16 + FXSYS_HexCharToInt(word.GetAt(i));
+  if (word[0] == '<') {
+    for (int i = 1; i < word.GetLength() && std::isxdigit(word[i]); ++i) {
+      num = num * 16 + FXSYS_HexCharToInt(word[i]);
       if (!num.IsValid())
         return 0;
     }
     return num.ValueOrDie();
   }
 
-  for (int i = 0; i < word.GetLength() && std::isdigit(word.GetAt(i)); ++i) {
-    num =
-        num * 10 + FXSYS_DecimalCharToInt(static_cast<wchar_t>(word.GetAt(i)));
+  for (int i = 0; i < word.GetLength() && std::isdigit(word[i]); ++i) {
+    num = num * 10 + FXSYS_DecimalCharToInt(static_cast<wchar_t>(word[i]));
     if (!num.IsValid())
       return 0;
   }
@@ -162,12 +161,12 @@ uint32_t CPDF_CMapParser::CMap_GetCode(const CFX_ByteStringC& word) {
 bool CPDF_CMapParser::CMap_GetCodeRange(CPDF_CMap::CodeRange& range,
                                         const CFX_ByteStringC& first,
                                         const CFX_ByteStringC& second) {
-  if (first.GetLength() == 0 || first.GetAt(0) != '<')
+  if (first.GetLength() == 0 || first[0] != '<')
     return false;
 
   int i;
   for (i = 1; i < first.GetLength(); ++i) {
-    if (first.GetAt(i) == '>') {
+    if (first[i] == '>') {
       break;
     }
   }
@@ -176,8 +175,8 @@ bool CPDF_CMapParser::CMap_GetCodeRange(CPDF_CMap::CodeRange& range,
     return false;
 
   for (i = 0; i < range.m_CharSize; ++i) {
-    uint8_t digit1 = first.GetAt(i * 2 + 1);
-    uint8_t digit2 = first.GetAt(i * 2 + 2);
+    uint8_t digit1 = first[i * 2 + 1];
+    uint8_t digit2 = first[i * 2 + 2];
     range.m_Lower[i] =
         FXSYS_HexCharToInt(digit1) * 16 + FXSYS_HexCharToInt(digit2);
   }
@@ -185,10 +184,10 @@ bool CPDF_CMapParser::CMap_GetCodeRange(CPDF_CMap::CodeRange& range,
   uint32_t size = second.GetLength();
   for (i = 0; i < range.m_CharSize; ++i) {
     uint8_t digit1 = ((uint32_t)i * 2 + 1 < size)
-                         ? second.GetAt((FX_STRSIZE)i * 2 + 1)
+                         ? second[static_cast<FX_STRSIZE>(i * 2 + 1)]
                          : '0';
     uint8_t digit2 = ((uint32_t)i * 2 + 2 < size)
-                         ? second.GetAt((FX_STRSIZE)i * 2 + 2)
+                         ? second[static_cast<FX_STRSIZE>(i * 2 + 2)]
                          : '0';
     range.m_Upper[i] =
         FXSYS_HexCharToInt(digit1) * 16 + FXSYS_HexCharToInt(digit2);
diff --git a/core/fpdfapi/font/cpdf_font.cpp b/core/fpdfapi/font/cpdf_font.cpp
index 82f9be3361..0fd8b45326 100644
--- a/core/fpdfapi/font/cpdf_font.cpp
+++ b/core/fpdfapi/font/cpdf_font.cpp
@@ -467,7 +467,7 @@ int CPDF_Font::FallbackGlyphFromCharcode(int fallbackFont, uint32_t charcode) {
     return -1;
 
   CFX_WideString str = UnicodeFromCharCode(charcode);
-  uint32_t unicode = !str.IsEmpty() ? str.GetAt(0) : charcode;
+  uint32_t unicode = !str.IsEmpty() ? str[0] : charcode;
   int glyph =
       FXFT_Get_Char_Index(m_FontFallbacks[fallbackFont]->GetFace(), unicode);
   if (glyph == 0)
diff --git a/core/fpdfapi/font/cpdf_tounicodemap.cpp b/core/fpdfapi/font/cpdf_tounicodemap.cpp
index 30bf0317ee..9076f4a737 100644
--- a/core/fpdfapi/font/cpdf_tounicodemap.cpp
+++ b/core/fpdfapi/font/cpdf_tounicodemap.cpp
@@ -147,7 +147,7 @@ void CPDF_ToUnicodeMap::Load(CPDF_Stream* pStream) {
           continue;
         }
         if (len == 1) {
-          m_Map[srccode] = destcode.GetAt(0);
+          m_Map[srccode] = destcode[0];
         } else {
           m_Map[srccode] = GetUnicode();
           m_MultiCharBuf.AppendChar(destcode.GetLength());
@@ -178,7 +178,7 @@ void CPDF_ToUnicodeMap::Load(CPDF_Stream* pStream) {
               continue;
             }
             if (len == 1) {
-              m_Map[code] = destcode.GetAt(0);
+              m_Map[code] = destcode[0];
             } else {
               m_Map[code] = GetUnicode();
               m_MultiCharBuf.AppendChar(destcode.GetLength());