The apex functions use SSE2 load/loadu/store/storeu and SSE streaming, with/without data pre-fetching depending on the situation. After that, it's gravy! So there are actually 3 self contained functions here, and they will select and use the most optimal one automatically!ģ) Most built-in memcpy/memmove functions (including MSVC and GCC) use an extremely optimized QWORD (64-bit) copy loop. This is a ONCE-off penalty the first time you call them. If none of these features are found, the functions will fall-back to using the built-in memcpy/memmove!Ģ) The first time you call either memcpy/memmove, they do a CPU feature detection (CPUID) and select the most optimal function for your CPU at runtime. 64-bit processors with SSE4.2 (Core i generation without penalties for unaligned memory), older 64-bit processors (Core, Core 2 and AMD equivalents) and 32-bit processors with SSE2. (I thought I would answer this question early as it must be on your mind!)ġ) This is NOT a SINGLE memcpy/memmove function, this is actually THREE separate functions with different caracteristics, algorithms and optimizations the code will choose the best function for the CPU at runtime, each function is built specifically for 3 different CPU architectures. Why is this faster than my built-in memcpy/memmove?Ī. For less than that I only have a 1 or 2 clock cycle penalty! But for all the other sizes, that title belongs to me! These functions will also reach your MAXIMUM memory bandwidth limits very quickly! Q. This code is faster for copies with size > 16 bytes. I think the only size I was consistently outperformed in Assembler was a 16-byte copy (and possibly some other small byte combinations, possibly also 8-bytes and 32-bytes if you optimize specifically to beat these algorithms).

Since optimizing for any one size is a tradeoff. The title of `fastest` does NOT belong to me for EVERY size copy. So of course I wanted to make a highly controvertial title, how many times have we seen `the fastest algorithm EVER` before but I needed your attention and I was successful in that! However, my title is not without justification!

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