# How fast is memset?

## How fast is memset?

We aren’t going to dig into the assembly for memset here, but the fastest possible memset would run at 32 bytes/cycle, limited by 1 store/cycle and maximum vector the width of 32 bytes on my machine, so the measured value of 29 bytes/cycle indicates it’s using an implementation something along those lines.

### Why does memset take an int?

memset predates (by quite a bit) the addition of function prototypes to C. Without a prototype, you can’t pass a char to a function — when/if you try, it’ll be promoted to int when you pass it, and what the function receives is an int .

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 memset faster than fill?

memset can be faster since it is written in assembler, whereas std::fill is a template function which simply does a loop internally.

## Why do you use 0 instead of 0 in Memset ( )?

But void *memset (void *s, int c, size_t n); second arg is an int so why are they recommending ‘\\0’ instead of 0? The memset () doc says “The memset () function shall copy c ( converted to an unsigned char) arg into each of the first n bytes of the object pointed to by s .” Is this more efficient or simply more explicit?

### Can you set an array to 10 in Memset?

Note that the above code doesn’t set array values to 10 as memset works character by character and an integer contains more than one bytes (or characters). However, if we replace 10 with -1, we get -1 values. Because representation of -1 contains all 1s in case of both char and int.

What is the syntax of Memset ( ) in C?

The syntax of memset () function is as follows : // ptr ==> Starting address of memory to be filled // x ==> Value to be filled // n ==> Number of bytes to be filled starting // from ptr to be filled void *memset (void *ptr, int x, size_t n); Note that ptr is a void pointer, so that we can pass any type of pointer to this function.

Which is faster movaps or Memset for SSE?

Target must be 8 byte aligned for the best performance. for chips with sse, movaps is fast, but only if the address is 16 byte aligned, so use a movsb until aligned, and then complete your clear with a loop of movaps