add memcpy

1 files changed, 14 insertions, 2 deletions

diff --git a/strings.c b/strings.c
index 4164467..94cb6ac 100644
--- a/strings.c
+++ b/strings.c
@@ -1,5 +1,3 @@
-#include <stddef.h>
-
 #include "strings.h"
 
 void uint32_to_dec(uint32_t number, char buf[10])
@@ -79,3 +77,17 @@ size_t strlen(char string[])
 
   return len;
 }
+
+void memcpy(void *dst, void *src, size_t nbytes)
+{
+  size_t iter;
+
+  // copying by word is faster than by byte
+  // copy by word as much as possible
+  for (iter = 0; iter < nbytes / 4; iter++)
+    ((volatile uint32_t*) dst)[iter] = ((uint32_t*) src)[iter];
+
+  // copy the remaining 1, 2 or 3 bytes by byte
+  for (iter *= 4; iter < nbytes; iter++)
+    ((volatile uint8_t*) dst)[iter] = ((uint8_t*) src)[iter];
+}