Save 8 bytes in each CFX_ByteString/WideString (on "LP64" platforms).

core/src/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>  // For offsetof().
+
 #include "../../include/fxcrt/fx_basic.h"
 #include "../../../third_party/base/numerics/safe_math.h"
 
 static int _Buffer_itoa(char* buf, int i, FX_DWORD flags)
 {
     if (i == 0) {
         buf[0] = '0';
         return 1;
     }
     char buf1[32];
@@ skipping 29 matching lines @@
     return CFX_ByteStringC(buf, _Buffer_itoa(buf, i, flags));
 }
 static CFX_StringData* FX_AllocString(int nLen)
 {
     // |nLen| is currently declared as in |int|. TODO(palmer): It should be
     // a |size_t|, or at least unsigned.
     if (nLen == 0 || nLen < 0) {
         return NULL;
     }
 
-    int overhead = sizeof(long) * 3 + 1;  // 3 longs in header plus 1 for NUL.
+    // Fixed portion of header plus a NUL char not included in m_nAllocLength.
+    // sizeof(FX_CHAR) is always 1, used for consistency with CFX_Widestring.
+    int overhead = offsetof(CFX_StringData, m_String) + sizeof(FX_CHAR);
     pdfium::base::CheckedNumeric<int> nSize = nLen;
     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 usableSize = totalSize - overhead;
@@ skipping 1066 matching lines @@
         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);
 }