auto import from //depot/cupcake/@135843
diff --git a/libc/arch-arm/bionic/strlen.c b/libc/arch-arm/bionic/strlen.c
new file mode 100644
index 0000000..01632e3
--- /dev/null
+++ b/libc/arch-arm/bionic/strlen.c
@@ -0,0 +1,129 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ * 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.
+ *
+ * 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>
+#include <stdint.h>
+#include <machine/cpu-features.h>
+
+size_t strlen(const char *s)
+{
+ __builtin_prefetch(s);
+ __builtin_prefetch(s+32);
+
+ union {
+ const char *b;
+ const uint32_t *w;
+ uintptr_t i;
+ } u;
+
+ // these are some scratch variables for the asm code below
+ uint32_t v, t;
+
+ // initialize the string length to zero
+ size_t l = 0;
+
+ // align the pointer to a 32-bit word boundary
+ u.b = s;
+ while (u.i & 0x3) {
+ if (__builtin_expect(*u.b++ == 0, 0)) {
+ goto done;
+ }
+ l++;
+ }
+
+ // loop for each word, testing if it contains a zero byte
+ // if so, exit the loop and update the length.
+ // We need to process 32 bytes per loop to schedule PLD properly
+ // and achieve the maximum bus speed.
+ asm(
+ "ldr %[v], [ %[s] ], #4 \n"
+ "sub %[l], %[l], %[s] \n"
+ "0: \n"
+#if __ARM_HAVE_PLD
+ "pld [ %[s], #64 ] \n"
+#endif
+ "sub %[t], %[v], %[mask], lsr #7\n"
+ "and %[t], %[t], %[mask] \n"
+ "bics %[t], %[t], %[v] \n"
+ "ldreq %[v], [ %[s] ], #4 \n"
+#if !defined(__OPTIMIZE_SIZE__)
+ "bne 1f \n"
+ "sub %[t], %[v], %[mask], lsr #7\n"
+ "and %[t], %[t], %[mask] \n"
+ "bics %[t], %[t], %[v] \n"
+ "ldreq %[v], [ %[s] ], #4 \n"
+ "bne 1f \n"
+ "sub %[t], %[v], %[mask], lsr #7\n"
+ "and %[t], %[t], %[mask] \n"
+ "bics %[t], %[t], %[v] \n"
+ "ldreq %[v], [ %[s] ], #4 \n"
+ "bne 1f \n"
+ "sub %[t], %[v], %[mask], lsr #7\n"
+ "and %[t], %[t], %[mask] \n"
+ "bics %[t], %[t], %[v] \n"
+ "ldreq %[v], [ %[s] ], #4 \n"
+ "bne 1f \n"
+ "sub %[t], %[v], %[mask], lsr #7\n"
+ "and %[t], %[t], %[mask] \n"
+ "bics %[t], %[t], %[v] \n"
+ "ldreq %[v], [ %[s] ], #4 \n"
+ "bne 1f \n"
+ "sub %[t], %[v], %[mask], lsr #7\n"
+ "and %[t], %[t], %[mask] \n"
+ "bics %[t], %[t], %[v] \n"
+ "ldreq %[v], [ %[s] ], #4 \n"
+ "bne 1f \n"
+ "sub %[t], %[v], %[mask], lsr #7\n"
+ "and %[t], %[t], %[mask] \n"
+ "bics %[t], %[t], %[v] \n"
+ "ldreq %[v], [ %[s] ], #4 \n"
+ "bne 1f \n"
+ "sub %[t], %[v], %[mask], lsr #7\n"
+ "and %[t], %[t], %[mask] \n"
+ "bics %[t], %[t], %[v] \n"
+ "ldreq %[v], [ %[s] ], #4 \n"
+#endif
+ "beq 0b \n"
+ "1: \n"
+ "add %[l], %[l], %[s] \n"
+ "tst %[v], #0xFF \n"
+ "beq 2f \n"
+ "add %[l], %[l], #1 \n"
+ "tst %[v], #0xFF00 \n"
+ "beq 2f \n"
+ "add %[l], %[l], #1 \n"
+ "tst %[v], #0xFF0000 \n"
+ "addne %[l], %[l], #1 \n"
+ "2: \n"
+ : [l]"=&r"(l), [v]"=&r"(v), [t]"=&r"(t), [s]"=&r"(u.b)
+ : "%[l]"(l), "%[s]"(u.b), [mask]"r"(0x80808080UL)
+ : "cc"
+ );
+
+done:
+ return l;
+}