29 Nov 2023 • C++ tricks: Production Ready TM aligned malloc

People generally implement aligned malloc by adding some metadata at ptr[-1] pointing to the actual allocation. In this post I will show you a simpler way.

void * Allocate( size_t size, size_t alignment ) {
    Assert( alignment <= 16 );
    return malloc( size );
}

This works because:

• Windows: "In Visual C++, the fundamental alignment is the alignment that's required for a double, or 8 bytes. In code that targets 64-bit platforms, it's 16 bytes."
• macOS: "The allocated memory is aligned such that it can be used for any data type, including AltiVec- and SSE-related types."
• Linux: "The address of a block returned by malloc or realloc in GNU systems is always a multiple of eight (or sixteen on 64-bit systems)."