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-rw-r--r--core/src/fxcrt/fx_basic_bstring.cpp18
1 files changed, 15 insertions, 3 deletions
diff --git a/core/src/fxcrt/fx_basic_bstring.cpp b/core/src/fxcrt/fx_basic_bstring.cpp
index 961aebe69c..2c8f7a766b 100644
--- a/core/src/fxcrt/fx_basic_bstring.cpp
+++ b/core/src/fxcrt/fx_basic_bstring.cpp
@@ -52,13 +52,25 @@ static CFX_StringData* FX_AllocString(int nLen)
if (nLen == 0 || nLen < 0) {
return NULL;
}
+
+ int overhead = sizeof(long) * 3 + 1; // 3 longs in header plus 1 for NUL.
pdfium::base::CheckedNumeric<int> nSize = nLen;
- nSize += sizeof(long) * 3 + 1;
- CFX_StringData* pData = (CFX_StringData*)FX_Alloc(FX_BYTE, nSize.ValueOrDie());
+ 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;
+ FXSYS_assert(usableSize >= nLen);
+
+ CFX_StringData* pData = (CFX_StringData*)FX_Alloc(FX_BYTE, totalSize);
if (!pData) {
return NULL;
}
- pData->m_nAllocLength = nLen;
+ pData->m_nAllocLength = usableSize;
pData->m_nDataLength = nLen;
pData->m_nRefs = 1;
pData->m_String[nLen] = 0;