Comment 18 for bug 655463

Interestingly enough:

strstr() and strcasestr() are only broken pre-SSE4, but memmem() is broken even on SSE4 machines.

On the other hand, on SSE4 machines, strstr() and strcasestr() are quadratic in behavior; in other words, the use of an assembly implementation has actually caused a performance regression over the fix for
http://sourceware.org/bugzilla/show_bug.cgi?id=5514

$ cat foo.c
#define _GNU_SOURCE
#include <string.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>

#define P ":012345678-"

static void quit (int sig) { exit (sig + 128); }
int main(int argc, char **argv)
{
  const char *hay = ";" ":013245678-" P P ":012345678." P ":012345678." P;
  const char *needle = P P P;

  size_t m = 1000000;
  char *largehay = malloc (2 * m + 2);
  char *largeneedle = malloc (m + 2);

  signal (SIGALRM, quit);
  alarm (5);
  if (!largehay || !largeneedle)
    return 2;
  memset (largehay, 'A', 2 * m);
  largehay[2 * m] = 'B';
  largehay[2 * m + 1] = 0;
  memset (largeneedle, 'A', m);
  largeneedle[m] = 'B';
  largeneedle[m + 1] = 0;

  switch (argc > 1 ? atoi (argv[1]) : 0)
    {
      /* Demonstrate str-two-way.h bug. */
    case 1:
      return !!memmem (hay, strlen (hay), needle, strlen (needle));
    case 2:
      return !!strstr (hay, needle);
    case 3:
      return !!strcasestr (hay, needle);

      /* Demonstrate quadratic behavior. */
    case 4:
      return !memmem (largehay, strlen (largehay),
        largeneedle, strlen (largeneedle));
    case 5:
      return !strstr (largehay, largeneedle);
    case 6:
      return !strcasestr (largehay, largeneedle);

      /* Usage error. */
    default:
      return 2;
    }
}
$ for i in $(seq 6); do ./foo $i; echo $?; done
1
0
0
0
142
142