faster splitter

[Patrick Schluter via Digitalmars-d]

On Friday, 27 May 2016 at 19:17:44 UTC, Chris wrote:
> Oops, I've been found out. :-) Thanks. You're right of course, 
> and I've already noticed that bug as it fails on not found. I 
> got the bounds wrong.

I had the same "bug" when I wrote my search function on the 
project at work. I also found out that using the simplest loop is 
the generally the best way to go. The processors nowaday have 
loop-caches, fast level1 caches etc, all the fancy search 
algorithms like Boyer-Moore etc. can only overcome their memory 
and initialisation overhead for really huge haystacks.

Here's the C code of my memmem() function that replaced the 
Boyer-Moore I had before. This implementation outran the BM 
search for sizes up to several hundreds megaytes on SPARC64 VII+ 
machine. On x86-64 I'm sure it would even be worse.

void * memmem(const void *haystack, size_t haystack_len, const 
void *needle, size_t needle_len)
{
   if(!haystack_len || !needle_len || needle_len > haystack_len)
     return NULL;

   uint8_t u8 = *((uint8_t *)needle);
   const uint8_t *p = (const uint8_t *) haystack;
   for(size_t i = haystack_len - needle_len + 1; i; --i) {
     if(*p == u8 && !memcmp(p, needle, needle_len))
       return (void *)p;
     else
       p++;
   }
   return NULL;
}

(sorry for posting C code, as I'm only beginning to learn D).