diff --git a/libc/arch-mips/string/strnlen.c b/libc/arch-mips/string/strnlen.c
new file mode 100644
index 0000000..2011deb
--- /dev/null
+++ b/libc/arch-mips/string/strnlen.c
@@ -0,0 +1,139 @@
+/*
+ * Copyright (c) 2017 Imagination Technologies.
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ *      * Redistributions of source code must retain the above copyright
+ *        notice, this list of conditions and the following disclaimer.
+ *      * Redistributions in binary form must reproduce the above copyright
+ *        notice, this list of conditions and the following disclaimer
+ *        in the documentation and/or other materials provided with
+ *        the distribution.
+ *      * Neither the name of Imagination Technologies nor the names of its
+ *        contributors may be used to endorse or promote products derived
+ *        from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <string.h>
+
+#define op_t                unsigned long int
+#define op_size             sizeof (op_t)
+
+#if __mips64 || __mips_isa_rev >= 2
+static inline size_t __attribute__ ((always_inline))
+do_bytes (const char *base, const char *p, op_t inval)
+{
+  op_t outval = 0;
+#if __mips64
+  __asm__ volatile (
+    "dsbh %1, %0 \n\t"
+    "dshd %0, %1 \n\t"
+    "dclz %1, %0 \n\t"
+    : "+r" (inval), "+r" (outval)
+  );
+#else
+  __asm__ volatile (
+    "wsbh %1, %0 \n\t"
+    "rotr %0, %1, 16 \n\t"
+    "clz %1, %0 \n\t"
+    : "+r" (inval), "+r" (outval)
+  );
+#endif
+  p += (outval >> 3);
+  return (size_t) (p - base);
+}
+
+#define DO_WORD(in, val) {                          \
+  op_t tmp = ((val - mask_1) & ~val) & mask_128;    \
+  if (tmp)                                          \
+    return do_bytes(str, (const char *)(in), tmp);  \
+}
+#else
+static inline size_t __attribute__ ((always_inline))
+do_bytes (const char *base, const char *p)
+{
+  for (; *p; ++p);
+  return (size_t) (p - base);
+}
+
+#define DO_WORD(in, val) {                     \
+  if (((val - mask_1) & ~val) & mask_128) {    \
+    return do_bytes(str, (const char *)(in));  \
+  }                                            \
+}
+#endif
+
+size_t strnlen (const char *str, size_t n) {
+  if (n != 0) {
+    const char *p = (const char *) str;
+    const op_t *w;
+    op_t mask_1, mask_128;
+
+    for (; n > 0 && ((size_t) p % op_size) != 0; --n, ++p) {
+      if (!(*p))
+        return (p - str);
+    }
+
+    w = (const op_t *) p;
+
+    __asm__ volatile (
+      "li %0, 0x01010101 \n\t"
+      : "=r" (mask_1)
+    );
+#if __mips64
+    mask_1 |= mask_1 << 32;
+#endif
+    mask_128 = mask_1 << 7;
+
+    /*
+     * Check op_size byteswize after initial alignment
+     */
+    while (n >= 4 * op_size) {
+      const op_t w0 = w[0];
+      const op_t w1 = w[1];
+      const op_t w2 = w[2];
+      const op_t w3 = w[3];
+      DO_WORD(w + 0, w0)
+      DO_WORD(w + 1, w1)
+      DO_WORD(w + 2, w2)
+      DO_WORD(w + 3, w3)
+      w += 4;
+      n -= 4 * op_size;
+    }
+
+    while (n >= op_size) {
+      DO_WORD(w, w[0]);
+      w++;
+      n -= op_size;
+    }
+
+    /*
+     * Check bytewize for remaining bytes
+     */
+    p = (const char *) w;
+    for (; n > 0; --n, ++p) {
+      if (!(*p))
+        return (p - str);
+    }
+
+    return (p - str);
+  }
+
+  return 0;
+}