Beef up unit test for CFX_ByteString and CFX_WideString.

core/fxcrt/fx_basic_bstring.cpp

 // Copyright 2014 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 <stddef.h>
 
 #include <cctype>
 
@@ skipping 402 matching lines @@
   // Don't release until done copying, might be one of the arguments.
   StringData* pOldData = m_pData;
   m_pData = StringData::Create(nNewLen);
   if (m_pData) {
     memcpy(m_pData->m_String, lpszSrc1Data, nSrc1Len);
     memcpy(m_pData->m_String + nSrc1Len, lpszSrc2Data, nSrc2Len);
   }
   pOldData->Release();
 }
 CFX_ByteString CFX_ByteString::Mid(FX_STRSIZE nFirst) const {
-  if (!m_pData) {
+  if (!m_pData)
     return CFX_ByteString();
-  }
+
   return Mid(nFirst, m_pData->m_nDataLength - nFirst);
 }
 CFX_ByteString CFX_ByteString::Mid(FX_STRSIZE nFirst, FX_STRSIZE nCount) const {
-  if (nFirst < 0) {
-    nFirst = 0;
-  }
-  if (nCount < 0) {
-    nCount = 0;
-  }
-  if (nFirst + nCount > m_pData->m_nDataLength) {
-    nCount = m_pData->m_nDataLength - nFirst;
-  }
-  if (nFirst > m_pData->m_nDataLength) {
-    nCount = 0;
-  }
-  if (nFirst == 0 && nFirst + nCount == m_pData->m_nDataLength) {
+  if (!m_pData)
+    return CFX_ByteString();
+
+  nFirst = std::min(std::max(0, nFirst), m_pData->m_nDataLength);
+  nCount = std::min(std::max(0, nCount), m_pData->m_nDataLength - nFirst);
+  if (nFirst == 0 && nCount == m_pData->m_nDataLength)
     return *this;
-  }
+
   CFX_ByteString dest;
   AllocCopy(dest, nCount, nFirst);
   return dest;
 }
 void CFX_ByteString::AllocCopy(CFX_ByteString& dest,
                                FX_STRSIZE nCopyLen,
                                FX_STRSIZE nCopyIndex) const {
   // |FX_STRSIZE| is currently typedef'd as in |int|. TODO(palmer): It
   // should be a |size_t|, or at least unsigned.
   if (nCopyLen == 0 || nCopyLen < 0) {
@@ skipping 625 matching lines @@
     fraction %= scale;
     scale /= 10;
   }
   return buf_size;
 }
 CFX_ByteString CFX_ByteString::FormatFloat(FX_FLOAT d, int precision) {
   FX_CHAR buf[32];
   FX_STRSIZE len = FX_ftoa(d, buf);
   return CFX_ByteString(buf, len);
 }