Make AARCH64 harder, better, faster, stronger

- Perform some housekeeping on scalar math function code
- Import ARM's Optimized Routines for SIMD string processing
- Upgrade to latest Chromium zlib and enable more SIMD optimizations

libc/intrin/strnlen.c

@@ -0,0 +1,61 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2021 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/assert.h"
+#include "libc/dce.h"
+#include "libc/intrin/asan.internal.h"
+#include "libc/intrin/bits.h"
+#include "libc/str/str.h"
+#ifndef __aarch64__
+
+static noasan size_t strnlen_x64(const char *s, size_t n, size_t i) {
+  uint64_t w;
+  for (; i + 8 < n; i += 8) {
+    w = *(uint64_t *)(s + i);
+    if ((w = ~w & (w - 0x0101010101010101) & 0x8080808080808080)) {
+      i += (unsigned)__builtin_ctzll(w) >> 3;
+      break;
+    }
+  }
+  return i;
+}
+
+/**
+ * Returns length of NUL-terminated string w/ limit.
+ *
+ * @param s is string
+ * @param n is max length
+ * @return byte length
+ * @asyncsignalsafe
+ */
+noasan size_t strnlen(const char *s, size_t n) {
+  size_t i;
+  if (IsAsan() && n) __asan_verify(s, 1);
+  for (i = 0; (uintptr_t)(s + i) & 7; ++i) {
+    if (i == n || !s[i]) return i;
+  }
+  i = strnlen_x64(s, n, i);
+  for (;; ++i) {
+    if (i == n || !s[i]) break;
+  }
+  _unassert(i == n || (i < n && !s[i]));
+  if (IsAsan()) __asan_verify(s, i);
+  return i;
+}
+
+#endif /* __aarch64__ */