Why is memcpy so slow?

Why is memcpy so slow?

I also had some code that I really needed to speed up, and memcpy is slow because it has too many unnecessary checks. For example, it checks to see if the destination and source memory blocks overlap and if it should start copying from the back of the block rather than the front.

What can I use instead of memcpy?

memmove() is similar to memcpy() as it also copies data from a source to destination. memcpy() leads to problems when source and destination addresses overlap as memcpy() simply copies data one by one from one location to another.

How can I speed up memcpy?

16 Answers. memcpy is likely to be the fastest way you can copy bytes around in memory. If you need something faster – try figuring out a way of not copying things around, e.g. swap pointers only, not the data itself.

How can I improve my memcpy performance?

Optimizing Memcpy improves speed

  1. Three basic memcpy() algorithms. The simplest memory-transfer algorithm just reads one byte at a time and writes that byte before reading the next.
  2. Block size.
  3. Data alignment.
  4. Caching.
  5. Write policy.
  6. Special situations.
  7. Optimize away.

Is memcpy faster than strcpy?

On almost any platform, memcpy() is going to be faster than strcpy() when copying the same number of bytes. The only time strcpy() or any of its “safe” equivalents would outperform memcpy() would be when the maximum allowable size of a string would be much greater than its actual size.

Is memset faster than memcpy?

zero_sizet is the fastest with roughly equal performance across -O1, -O2 and -O3. memset was always slower than zero_sizet. (twice as slow for -O3). one thing of interest is that at -O3 zero_1 was equally fast as zero_sizet.

Is Memmove faster than memcpy?

The difference between memcpy and memmove is simple: when the source and destination blocks of memory overlap (for example, if they are the same), memmove works, but memcpy ‘s behavior is undefined. memcpy can be faster, and usually is.

Which is faster memcpy or assignment?

1 Answer. You should never expect them outperform assignments. The reason is, the compiler will use memcpy anyway when it thinks it would be faster (if you use optimize flags).

Is Strncpy faster than strcpy?

Should I use memcpy or strcpy?

for encrypted data or binary data, memcpy is ideal way to go. strcpy is deprecated, so use strncpy . The main difference is that memcpy() always copies the exact number of bytes you specify; strcpy() , on the other hand, will copy until it reads a NUL (aka 0) byte, and then stop after that.

Does memset use SIMD?

GCC 11 now favors using SIMD registers for doing inlined memset and memcpy whenever the amount to be copied or set is smaller than 256 bytes (unless optimizing for code size, in which case the limit is set to 128 bytes).

Is memset faster than for loop?

7 Answers. Most certainly, memset will be much faster than that loop. Note how you treat one character at a time, but those functions are so optimized that set several bytes at a time, even using, when available, MMX and SSE instructions.