Benchmarks should allocate with cacheline (often 64 bytes) alignment
to avoid unreliable timings. This technique, storing the offset in the
byte before the pointer, doesn't require C11's aligned_alloc for
compatibility with older compilers.
For example, Glibc's x86_64 malloc returns 16-byte aligned buffers, which is
not sufficient for AVX/AVX2 (32-byte preferred) or AVX512 (64-byte).