[liba] Add memmove to string.h

Change-Id: I99b412dc7404e2711dbf7753f0d619694dee3d19

liba/Makefile

@@ -12,6 +12,7 @@ objs += $(addprefix liba/src/, \
   isinff.o \
   malloc.o \
   memcpy.o \
+  memmove.o \
   memset.o \
   strcmp.o \
   strlcpy.o \

liba/include/string.h

@@ -7,6 +7,7 @@
 LIBA_BEGIN_DECLS
 
 void * memcpy(void * dst, const void * src, size_t n);
+void * memmove(void * dst, const void * src, size_t n);
 void * memset(void * b, int c, size_t len);
 size_t strlen(const char * s);
 int strcmp(const char *s1, const char *s2);

liba/src/memmove.c

@@ -0,0 +1,21 @@
+#include <string.h>
+
+void * memmove(void * dst, const void * src, size_t n) {
+  char * destination = (char *)dst;
+  char * source = (char *)src;
+
+  if (source < destination && destination < source + n) {
+    /* Copy backwards to avoid overwrites */
+    source += n;
+    destination += n;
+    while (n--) {
+      *--destination = *--source;
+    }
+  } else {
+    while (n--) {
+      *destination++ = *source++;
+    }
+  }
+
+  return dst;
+}