4 files changed, 47 insertions, 6 deletions
diff --git a/lib/include/common.h b/lib/include/common.h
index 1e48097..d006d71 100644
--- a/lib/include/common.h
+++ b/lib/include/common.h
@@ -15,3 +15,5 @@
 
 
 void* memset(void* s, int c, size_t n);
+void* memcpy(void* d, const void* s, size_t n);
+
diff --git a/lib/src/common.c b/lib/src/common.c
index 2d122f5..dd806bf 100644
--- a/lib/src/common.c
+++ b/lib/src/common.c
@@ -16,3 +16,23 @@ void* memset(void* s, int c, size_t n) {
         : "memory");
     return s;
 }
+
+void* memcpy(void* d, const void* s, size_t n) {
+    // When `d` points into `[s, s+n[` we would override `s` while copying into `d`.
+    //   |------------|--------|
+    //   s            d        s+n
+    // -> We don't support.
+    //
+    // When `d` points into `]s-n, s[` it is destructive for `s` but all data
+    // from `s` are copied into `d`. The user gets what he asks for.
+    // -> Supported.
+    ERROR_ON(s <= d && d < (void*)((unsigned char*)s + n), "memcpy: Unsupported overlap!");
+    asm volatile(
+        "cld"
+        "\n"
+        "rep movsb"
+        : "+D"(d), "+S"(s), "+c"(n)
+        :
+        : "memory");
+    return d;
+}
diff --git a/test/checker.cc b/test/checker.cc
index d687b72..3d425bf 100644
--- a/test/checker.cc
+++ b/test/checker.cc
@@ -3,7 +3,8 @@
 #include "test_helper.h"
 
 extern "C" {
-    #include <fmt.h>
+#include <common.h>
+#include <fmt.h>
 }
 
 void check_dec() {
@@ -84,6 +85,27 @@ void check_exceed_len() {
     ASSERT_EQ('\0', have[7]);
 }
 
+void check_memset() {
+    unsigned char d[7] = {0};
+    void* ret = memset(d, '\x42', sizeof(d));
+
+    ASSERT_EQ(ret, d);
+    for (unsigned i = 0; i < sizeof(d); ++i) {
+        ASSERT_EQ(0x42, d[i]);
+    }
+}
+
+void check_memcpy() {
+    unsigned char s[5] = {5, 4, 3, 2, 1};
+    unsigned char d[5] = {0};
+    void* ret = memcpy(d, s, sizeof(d));
+
+    ASSERT_EQ(ret, d);
+    for (unsigned i = 0; i < sizeof(d); ++i) {
+        ASSERT_EQ(5-i, d[i]);
+    }
+}
+
 int main() {
     TEST_INIT;
     TEST_ADD(check_dec);
@@ -95,5 +117,7 @@ int main() {
     TEST_ADD(check_null);
     TEST_ADD(check_exact_len);
     TEST_ADD(check_exceed_len);
+    TEST_ADD(check_memset);
+    TEST_ADD(check_memcpy);
     return TEST_RUN;
 }
diff --git a/test/test_helper.h b/test/test_helper.h
index b78d9a6..f1356a4 100644
--- a/test/test_helper.h
+++ b/test/test_helper.h
@@ -28,11 +28,6 @@ void ASSERT_EQ(T1 expected, T2 have) {
     }
 }
 
-template<typename T1, typename T2>
-void ASSERT_EQ(T1* expected, T2* have) {
-    ASSERT_EQ(*expected, *have);
-}
-
 // Char string based ASSERT_* helper.
 
 template<>