Add more missing libc functionality

libc/str/str.h

@@ -118,6 +118,7 @@ wchar_t *wcschr(const wchar_t *, wchar_t) strlenesque;
 wchar_t *wmemchr(const wchar_t *, wchar_t, size_t) strlenesque;
 wchar_t *wcschrnul(const wchar_t *, wchar_t) strlenesque returnsnonnull;
 char *strstr(const char *, const char *) strlenesque;
+char *strcasestr(const char *, const char *) strlenesque;
 char16_t *strstr16(const char16_t *, const char16_t *) strlenesque;
 wchar_t *wcsstr(const wchar_t *, const wchar_t *) strlenesque;
 void *rawwmemchr(const void *, wchar_t) strlenesque returnsnonnull;

libc/str/strcasestr.c

@@ -0,0 +1,70 @@
+/*-*- 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 2020 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/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 substring case-insensitively.
+ *
+ * @param haystack is the search area, as a NUL-terminated string
+ * @param needle is the desired substring, also NUL-terminated
+ * @return pointer to first substring within haystack, or NULL
+ * @note this implementation goes fast in practice but isn't hardened
+ *     against pathological cases, and therefore shouldn't be used on
+ *     untrustworthy data
+ * @asyncsignalsafe
+ * @see strstr()
+ */
+noasan char *strcasestr(const char *haystack, const char *needle) {
+  char c;
+  xmm_t *p;
+  size_t i;
+  unsigned k, m;
+  xmm_t v, n1, n2, z = {0};
+  if (IsAsan()) __asan_verify(needle, 1);
+  if (IsAsan()) __asan_verify(haystack, 1);
+  if (haystack == needle || !*needle) return haystack;
+  c = *needle;
+  n1 = (xmm_t){c, c, c, c, c, c, c, c, c, c, c, c, c, c, c, c};
+  c = kToLower[c & 255];
+  n2 = (xmm_t){c, c, c, c, c, c, c, c, c, c, c, c, c, c, c, c};
+  for (;;) {
+    k = (uintptr_t)haystack & 15;
+    p = (const xmm_t *)((uintptr_t)haystack & -16);
+    v = *p;
+    m = __builtin_ia32_pmovmskb128((v == z) | (v == n1) | (v == n2));
+    m >>= k;
+    m <<= k;
+    while (!m) {
+      v = *++p;
+      m = __builtin_ia32_pmovmskb128((v == z) | (v == n1) | (v == n2));
+    }
+    haystack = (const char *)p + __builtin_ctzl(m);
+    for (i = 0;; ++i) {
+      if (!needle[i]) return (/*unconst*/ char *)haystack;
+      if (!haystack[i]) break;
+      if (kToLower[needle[i] & 255] != kToLower[haystack[i] & 255]) break;
+    }
+    if (!*haystack++) break;
+  }
+  return 0;
+}

libc/str/strstr.c

@@ -32,6 +32,7 @@ typedef char xmm_t __attribute__((__vector_size__(16), __aligned__(16)));
  *     against pathological cases, and therefore shouldn't be used on
  *     untrustworthy data
  * @asyncsignalsafe
+ * @see strcasestr()
  * @see memmem()
  */
 noasan char *strstr(const char *haystack, const char *needle) {