Make StringData a templated class.

core/fxcrt/cfx_string_data_template.h

Index: core/fxcrt/cfx_string_data_template.h
diff --git a/core/fxcrt/cfx_string_data_template.h b/core/fxcrt/cfx_string_data_template.h
new file mode 100644
index 0000000000000000000000000000000000000000..b53b2511c277769a940e74ca4ef53d105d42184f
--- /dev/null
+++ b/core/fxcrt/cfx_string_data_template.h
@@ -0,0 +1,115 @@
+// Copyright 2016 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
+
+#ifndef CORE_FXCRT_CFX_STRING_DATA_TEMPLATE_H_
+#define CORE_FXCRT_CFX_STRING_DATA_TEMPLATE_H_
+
+#include "core/fxcrt/include/fx_memory.h"
+#include "core/fxcrt/include/fx_system.h"
+#include "third_party/base/numerics/safe_math.h"
+
+template <typename CharType>
+class CFX_StringDataTemplate {
+ public:
+  static CFX_StringDataTemplate* Create(FX_STRSIZE nLen) {
+    FXSYS_assert(nLen > 0);
+
+    // Calculate space needed for the fixed portion of the struct plus the
+    // NUL char that is not included in |m_nAllocLength|.
+    int overhead =
+        offsetof(CFX_StringDataTemplate, m_String) + sizeof(CharType);
+    pdfium::base::CheckedNumeric<int> nSize = nLen;
+    nSize *= sizeof(CharType);
+    nSize += overhead;
+
+    // Now round to an 8-byte boundary. We'd expect that this is the minimum
+    // granularity of any of the underlying allocators, so there may be cases
+    // where we can save a re-alloc when adding a few characters to a string
+    // by using this otherwise wasted space.
+    nSize += 7;
+    int totalSize = nSize.ValueOrDie() & ~7;
+    int usableLen = (totalSize - overhead) / sizeof(CharType);
+    FXSYS_assert(usableLen >= nLen);
+
+    void* pData = FX_Alloc(uint8_t, totalSize);
+    return new (pData) CFX_StringDataTemplate(nLen, usableLen);
+  }
+
+  static CFX_StringDataTemplate* Create(const CFX_StringDataTemplate& other) {
+    CFX_StringDataTemplate* result = Create(other.m_nDataLength);
+    result->CopyContents(other);
+    return result;
+  }
+
+  static CFX_StringDataTemplate* Create(const CharType* pStr, FX_STRSIZE nLen) {
+    CFX_StringDataTemplate* result = Create(nLen);
+    result->CopyContents(pStr, nLen);
+    return result;
+  }
+
+  void Retain() { ++m_nRefs; }
+  void Release() {
+    if (--m_nRefs <= 0)
+      FX_Free(this);
+  }
+
+  bool CanOperateInPlace(FX_STRSIZE nTotalLen) const {
+    return m_nRefs <= 1 && nTotalLen <= m_nAllocLength;
+  }
+
+  void CopyContents(const CFX_StringDataTemplate& other) {
+    FXSYS_assert(other.m_nDataLength <= m_nAllocLength);
+    FXSYS_memcpy(m_String, other.m_String,
+                 (other.m_nDataLength + 1) * sizeof(CharType));
+  }
+
+  void CopyContents(const CharType* pStr, FX_STRSIZE nLen) {
+    FXSYS_assert(nLen >= 0 && nLen <= m_nAllocLength);
+    FXSYS_memcpy(m_String, pStr, nLen * sizeof(CharType));
+    m_String[nLen] = 0;
+  }
+
+  void CopyContentsAt(FX_STRSIZE offset,
+                      const CharType* pStr,
+                      FX_STRSIZE nLen) {
+    FXSYS_assert(offset >= 0 && nLen >= 0 && offset + nLen <= m_nAllocLength);
+    FXSYS_memcpy(m_String + offset, pStr, nLen * sizeof(CharType));
+    m_String[offset + nLen] = 0;
+  }
+
+  // To ensure ref counts do not overflow, consider the worst possible case:
+  // the entire address space contains nothing but pointers to this object.
+  // Since the count increments with each new pointer, the largest value is
+  // the number of pointers that can fit into the address space. The size of
+  // the address space itself is a good upper bound on it.
+  intptr_t m_nRefs;  // Would prefer ssize_t, but no windows support.
+
+  // |FX_STRSIZE| is currently typedef'd as |int|.
+  // TODO(palmer): It should be a |size_t|, or at least unsigned.
+  // These lengths are in terms of number of characters, not bytes, and do not
+  // include the terminating NUL character, but the underlying buffer is sized
+  // to be capable of holding it.
+  FX_STRSIZE m_nDataLength;
+  FX_STRSIZE m_nAllocLength;
+
+  // Not really 1, variable size.
+  CharType m_String[1];
+
+ private:
+  CFX_StringDataTemplate(FX_STRSIZE dataLen, FX_STRSIZE allocLen)
+      : m_nRefs(0), m_nDataLength(dataLen), m_nAllocLength(allocLen) {
+    FXSYS_assert(dataLen >= 0);
+    FXSYS_assert(dataLen <= allocLen);
+    m_String[dataLen] = 0;
+  }
+
+  ~CFX_StringDataTemplate() = delete;
+};
+
+extern template class CFX_StringDataTemplate<FX_CHAR>;
+extern template class CFX_StringDataTemplate<FX_WCHAR>;
+
+#endif  // CORE_FXCRT_CFX_STRING_DATA_TEMPLATE_H_