Make more libc improvements

- Make memmem() faster
- Make readdir() thread safe
- Remove 64kb limit from mkdeps.com
- Add old crypt() function from Musl
- Improve new fix-third-party.py tool
- Improve libc/isystem/ headers and fix bugs

libc/str/memmem.c

@@ -16,8 +16,13 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/bits/likely.h"
+#include "libc/dce.h"
+#include "libc/intrin/asan.internal.h"
 #include "libc/str/str.h"
 
+typedef char xmm_t __attribute__((__vector_size__(16), __aligned__(16)));
+
 /**
  * Searches for fixed-length substring in memory region.
  *
@@ -27,26 +32,41 @@
  * @param needlelen is its character count
  * @return pointer to first result or NULL if not found
  */
-void *memmem(const void *haystack, size_t haystacklen, const void *needle,
-             size_t needlelen) {
-  size_t i, j;
-  const char *p;
+noasan void *memmem(const void *haystack, size_t haystacklen,
+                    const void *needle, size_t needlelen) {
+  char c;
+  xmm_t n, *v;
+  unsigned i, k, m;
+  const char *p, *q, *e;
+  if (IsAsan()) __asan_verify(needle, needlelen);
+  if (IsAsan()) __asan_verify(haystack, haystacklen);
   if (!needlelen) return haystack;
-  if (needlelen <= haystacklen) {
-    p = memchr(haystack, *(const char *)needle, haystacklen);
-    if (needlelen == 1) return p;
-    if (p) {
-      haystacklen -= p - (const char *)haystack;
-      haystack = p;
+  if (UNLIKELY(needlelen > haystacklen)) return 0;
+  q = needle;
+  c = *q;
+  n = (xmm_t){c, c, c, c, c, c, c, c, c, c, c, c, c, c, c, c};
+  p = haystack;
+  e = p + haystacklen;
+  k = (uintptr_t)p & 15;
+  v = (const xmm_t *)((uintptr_t)p & -16);
+  m = __builtin_ia32_pmovmskb128(*v == n);
+  m >>= k;
+  m <<= k;
+  for (;;) {
+    while (!m) {
+      ++v;
+      if ((const char *)v >= e) return 0;
+      m = __builtin_ia32_pmovmskb128(*v == n);
     }
-    /* TODO: make not quadratic */
-    for (i = 0; i < haystacklen; ++i) {
-      for (j = 0;; ++j) {
-        if (j == needlelen) return (/*unconst*/ char *)haystack + i;
-        if (i + j == haystacklen) break;
-        if (((char *)needle)[j] != ((char *)haystack)[i + j]) break;
+    do {
+      k = __builtin_ctzl(m);
+      p = (const char *)v + k;
+      if (UNLIKELY(p + needlelen > e)) return 0;
+      for (i = 1;; ++i) {
+        if (i == needlelen) return (/*unconst*/ char *)p;
+        if (p[i] != q[i]) break;
       }
-    }
+      m &= ~(1 << k);
+    } while (m);
   }
-  return NULL;
 }