Initial Contribution

libc/string/memmove.c

@@ -0,0 +1,72 @@
+/*
+ * 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>
+
+void *memmove(void *dst, const void *src, size_t n)
+{
+  const char *p = src;
+  char *q = dst;
+  if (__builtin_expect(q < p, 1)) {
+    return memcpy(dst, src, n);
+  } else {
+#define PRELOAD_DISTANCE 64
+      /* a semi-optimized memmove(). we're preloading the src and dst buffers
+       * as we go */
+    size_t c0, c1, i;
+    p += n;
+    q += n;
+    /* note: we preload the destination as well, because the 1-byte at a time
+     * copy below doesn't take advantage of the write-buffer, we need
+     * to use the cache instead as a poor man's write-combiner */
+    __builtin_prefetch(p-1);
+    __builtin_prefetch(q-1);
+    if (PRELOAD_DISTANCE > 32) {
+        __builtin_prefetch(p-(32+1));
+        __builtin_prefetch(q-(32+1));
+    }
+    /* do the prefetech as soon as possible, prevent the compiler to
+     * reorder the instructions above the prefetch */
+    asm volatile("":::"memory");
+    c0 = n & 0x1F; /* cache-line is 32 bytes */
+    c1 = n >> 5;
+    while ( c1-- ) {
+        /* ARMv6 can have up to 3 memory access outstanding */
+      __builtin_prefetch(p - (PRELOAD_DISTANCE+1));
+      __builtin_prefetch(q - (PRELOAD_DISTANCE+1));
+      asm volatile("":::"memory");
+      for (i=0 ; i<32 ; i++) {
+        *--q = *--p;
+      }
+    }
+    while ( c0-- ) {
+      *--q = *--p;
+    }
+  }
+
+  return dst;
+}