Re: Unaligned memory access

Em sábado, 14 de fevereiro de 2026 às 14:00:40 UTC, Sainan escreveu:

lua_newuserdata does not provide alignment guarantees, but practically, you 
will see that it is only 8-byte aligned (on 64-bit). Of course, your 
workaround of using 'new' works, but you can also simply allocate 15 more 
bytes so you can safely offset the pointer: 

char *data = reinterpret_cast<char*>(lua_newuserdata(L, data_len + 15)); 
if (reinterpret_cast<uintptr_t>(data) % 16) { /* data is not 16-byte 
aligned? */ 
data = reinterpret_cast<char*>(reinterpret_cast<uintptr_t>(data) + (16 - 
(reinterpret_cast<uintptr_t>(data) % 16))); /* align data to 16-byte 
boundary */ 
} 

-- Sainan 


Good idea, I ended up using it instead of the additional pointer 
indirection:

ud = (ud + 15) & ~(uintptr_t)15;

Andre

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