static void setDefaultAllocator( TidyBuffer* buf )
{
    buf->allocator = &TY_(g_default_allocator);
}

/* Avoid thrashing memory by doubling buffer size
** until larger than requested size.
   buf->allocated is bigger than allocSize+1 so that a trailing null byte is
   always available.
*/
void TIDY_CALL tidyBufCheckAlloc( TidyBuffer* buf, uint allocSize, uint chunkSize )
{
    assert( buf != NULL );

    if ( !buf->allocator )
        setDefaultAllocator( buf );

    if ( 0 == chunkSize )
        chunkSize = 256;
    if ( allocSize+1 > buf->allocated ) {
        byte* bp;
        uint allocAmt = chunkSize;
        if ( buf->allocated > 0 )
            allocAmt = buf->allocated;
        while ( allocAmt < allocSize+1 )
            allocAmt *= 2;

        bp = (byte*)TidyRealloc( buf->allocator, buf->bp, allocAmt );
        if ( bp != NULL )
        {
            TidyClearMemory( bp + buf->allocated, allocAmt - buf->allocated );
            buf->bp = bp;
            buf->allocated = allocAmt;
        }
    }
}