There is an interesting related problem - how do you efficiently test if a buffer contains only zeroes? We use this for automatically sparsifying disk images. There's no standard C function for this. My colleague came up with the following nice trick. It reuses the (presumably already maximally optimized) memcmp function from libc:
https://gitlab.com/nbdkit/nbdkit/-/blob/b31859402d1404ba0433...
static inline bool __attribute__((__nonnull__ (1)))
is_zero (const char *buffer, size_t size)
{
size_t i;
const size_t limit = size < 16 ? size : 16;
for (i = 0; i < limit; ++i)
if (buffer[i])
return false;
if (size != limit)
return ! memcmp (buffer, buffer + 16, size - 16);
return true;
}