wcsmbs: optimize wcpncpy

This patch rewrites wcpncpy using wcslen, wmemcpy, and wmemset.  This is
similar to the optimization done on stpncpy by 48497ab.

Checked on x86_64-linux-gnu.

        * wcsmbs/wcpncpy.c (__wcpcpy): Rewrite using wcslen, wmemcpy, and
	wmemset.

ChangeLog

@@ -1,5 +1,8 @@
 2019-02-27  Adhemerval Zanella  <[email protected]>
 
+	* wcsmbs/wcpncpy.c (__wcpcpy): Rewrite using wcslen, wmemcpy, and
+	wmemset.
+
 	* sysdeps/m68k/wcpcpy.c: Remove file.
 	* wcsmbs/wcpcpy.c (__wcpcpy): Rewrite using wcslen and wmemcpy.
 

wcsmbs/wcpncpy.c

@@ -27,59 +27,12 @@
 wchar_t *
 __wcpncpy (wchar_t *dest, const wchar_t *src, size_t n)
 {
-  wint_t c;
-  wchar_t *const s = dest;
-
-  if (n >= 4)
-    {
-      size_t n4 = n >> 2;
-
-      for (;;)
-	{
-	  c = *src++;
-	  *dest++ = c;
-	  if (c == L'\0')
-	    break;
-	  c = *src++;
-	  *dest++ = c;
-	  if (c == L'\0')
-	    break;
-	  c = *src++;
-	  *dest++ = c;
-	  if (c == L'\0')
-	    break;
-	  c = *src++;
-	  *dest++ = c;
-	  if (c == L'\0')
-	    break;
-	  if (--n4 == 0)
-	    goto last_chars;
-	}
-      n -= dest - s;
-      goto zero_fill;
-    }
-
- last_chars:
-  n &= 3;
-  if (n == 0)
+  size_t size = __wcsnlen (src, n);
+  __wmemcpy (dest, src, size);
+  dest += size;
+  if (size == n)
     return dest;
-
-  for (;;)
-    {
-      c = *src++;
-      --n;
-      *dest++ = c;
-      if (c == L'\0')
-	break;
-      if (n == 0)
-	return dest;
-    }
-
- zero_fill:
-  while (n-- > 0)
-    dest[n] = L'\0';
-
-  return dest - 1;
+  return wmemset (dest, L'\0', (n - size));
 }
 
 #ifndef WCPNCPY