Introduce OStringBuffer::appendUninitialized

...corresponding to the OUStringBuffer couterpart

Change-Id: I3ab03343696e6755cf1ccc470e4decc2f41d2558

include/rtl/strbuf.h

@@ -101,7 +101,9 @@ SAL_DLLPUBLIC void SAL_CALL rtl_stringbuffer_ensureCapacity(
     @param[in,out]  This        the String to operate on.
     @param[in,out]  capacity    the capacity of the string buffer
     @param[in]      offset      the offset.
-    @param[in]      str         a character array.
+    @param[in]      str         a character array.  Since LibreOffice 4.4, as a
+                                special case, if str is null then the len added
+                                characters are left uninitialized.
     @param[in]      len         the number of characters to append.
  */
 SAL_DLLPUBLIC void SAL_CALL rtl_stringbuffer_insert(

include/rtl/strbuf.hxx

@@ -490,6 +490,7 @@ public:
     OStringBuffer & append( const sal_Char * str, sal_Int32 len)
     {
         assert( len >= 0 );
+        assert( len == 0 || str != 0 );
         rtl_stringbuffer_insert( &pData, &nCapacity, getLength(), str, len );
         return *this;
     }
@@ -644,6 +645,28 @@ public:
         return append( sz, rtl_str_valueOfDouble( sz, d ) );
     }
 
+    /**
+       Unsafe way to make space for a fixed amount of characters to be appended
+       into this OStringBuffer.
+
+       A call to this function must immediately be followed by code that
+       completely fills the uninitialized block pointed to by the return value.
+
+       @param length the length of the uninitialized block of char entities;
+       must be non-negative
+
+       @return a pointer to the start of the uninitialized block; only valid
+       until this OStringBuffer's capacity changes
+
+       @since LibreOffice 4.4
+    */
+    char * appendUninitialized(sal_Int32 length) {
+        assert(length >= 0);
+        sal_Int32 n = getLength();
+        rtl_stringbuffer_insert(&pData, &nCapacity, n, 0, length);
+        return pData->buffer + n;
+    }
+
     /**
         Inserts the string into this string buffer.
 
@@ -729,6 +752,7 @@ public:
     {
         assert( offset >= 0 && offset <= pData->length );
         assert( len >= 0 );
+        assert( len == 0 || str != 0 );
         rtl_stringbuffer_insert( &pData, &nCapacity, offset, str, len );
         return *this;
     }

sal/rtl/math.cxx

@@ -222,6 +222,7 @@ struct StringTraits
                                    sal_Int32 * pOffset, sal_Char const * pChars,
                                    sal_Int32 nLen)
     {
+        assert(pChars != nullptr);
         rtl_stringbuffer_insert(pBuffer, pCapacity, *pOffset, pChars, nLen);
         *pOffset += nLen;
     }
@@ -230,6 +231,7 @@ struct StringTraits
                                    sal_Int32 * pOffset, sal_Char const * pStr,
                                    sal_Int32 nLen)
     {
+        assert(pStr != nullptr);
         rtl_stringbuffer_insert(pBuffer, pCapacity, *pOffset, pStr, nLen);
         *pOffset += nLen;
     }

sal/rtl/strbuf.cxx

@@ -114,11 +114,14 @@ void SAL_CALL rtl_stringbuffer_insert( rtl_String ** This,
             memmove( pBuf + offset + len, pBuf + offset, n * sizeof(sal_Char) );
 
         /* insert the new characters */
-        if( len == 1 )
+        if( str != nullptr )
+        {
+            if( len == 1 )
                             /* optimized for 1 character */
-            pBuf[offset] = *str;
-        else
-            memcpy( pBuf + offset, str, len * sizeof(sal_Char) );
+                pBuf[offset] = *str;
+            else
+                memcpy( pBuf + offset, str, len * sizeof(sal_Char) );
+        }
         (*This)->length = nOldLen + len;
         pBuf[ nOldLen + len ] = 0;
     }