Make improvements

libc/str/memcmp.c

@@ -0,0 +1,54 @@
+/*-*- 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                              │
+│                                                                              │
+│ This program is free software; you can redistribute it and/or modify         │
+│ it under the terms of the GNU General Public License as published by         │
+│ the Free Software Foundation; version 2 of the License.                      │
+│                                                                              │
+│ This program is distributed in the hope that it will be useful, but          │
+│ WITHOUT ANY WARRANTY; without even the implied warranty of                   │
+│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU             │
+│ General Public License for more details.                                     │
+│                                                                              │
+│ You should have received a copy of the GNU General Public License            │
+│ along with this program; if not, write to the Free Software                  │
+│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA                │
+│ 02110-1301 USA                                                               │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/intrin/pcmpeqb.h"
+#include "libc/intrin/pmovmskb.h"
+#include "libc/nexgen32e/bsf.h"
+#include "libc/str/str.h"
+
+/**
+ * Compares memory.
+ *
+ * @return unsigned char subtraction at stop index
+ * @asyncsignalsafe
+ */
+int memcmp(const void *a, const void *b, size_t n) {
+  int c;
+  size_t i;
+  unsigned m;
+  uint8_t *p1, *p2;
+  uint8_t v1[16], v2[16];
+  if (n) {
+    for (p1 = a, p2 = b, i = 0; i + 16 <= n; i += 16) {
+      memcpy(v1, p1 + i, 16);
+      memcpy(v2, p2 + i, 16);
+      pcmpeqb(v1, v1, v2);
+      if ((m = pmovmskb(v1) - 0xffff)) {
+        i += bsf(m);
+        return p1[i] - p2[i];
+      }
+    }
+    for (; i < n; ++i) {
+      if ((c = p1[i] - p2[i])) {
+        return c;
+      }
+    }
+  }
+  return 0;
+}