Add minor improvements and cleanup

libc/str/strcpy.c

@@ -17,7 +17,10 @@
 │ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA                │
 │ 02110-1301 USA                                                               │
 ╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/intrin/pcmpeqb.h"
+#include "libc/intrin/pmovmskb.h"
 #include "libc/limits.h"
+#include "libc/nexgen32e/bsf.h"
 #include "libc/str/str.h"
 
 /**
@@ -31,6 +34,30 @@
  * @asyncsignalsafe
  */
 char *strcpy(char *d, const char *s) {
-  memccpy(d, s, '\0', SIZE_MAX);
-  return d;
+  size_t i;
+  uint8_t v1[16], v2[16], vz[16];
+  i = 0;
+  while (((uintptr_t)(s + i) & 15)) {
+    if (!(d[i] = s[i])) {
+      return d;
+    }
+    ++i;
+  }
+  for (;;) {
+    memset(vz, 0, 16);
+    memcpy(v1, s + i, 16);
+    pcmpeqb(v2, v1, vz);
+    if (!pmovmskb(v2)) {
+      memcpy(d + i, v1, 16);
+      i += 16;
+    } else {
+      break;
+    }
+  }
+  for (;;) {
+    if (!(d[i] = s[i])) {
+      return d;
+    }
+    ++i;
+  }
 }