libc: Add memcmp() and memmove()

Those were there since forever in the kernel, but they haven't been added to libc until now.

libs/libc/include/string.h

@@ -18,6 +18,12 @@ extern "C"
     /* Searches for the character c in n bytes of buf. */
     void* memchr(const void* buf, int c, size_t n);
 
+    /* Compares n bytes of memory at a and b. */
+    int memcmp(const void* a, const void* b, size_t n);
+
+    /* Copies n bytes from src to dst. Can be used if src and dst overlap. */
+    void* memmove(void* dest, const void* src, size_t n);
+
     /* Returns a heap-allocated copy of the string str. Should be freed when it is not used anymore. */
     char* strdup(const char* str);
 

libs/libc/src/string.cpp

@@ -25,6 +25,27 @@ extern "C"
         return NULL;
     }
 
+    int memcmp(const void* a, const void* b, size_t n)
+    {
+        const char* _a = (const char*)a;
+        const char* _b = (const char*)b;
+        for (; n && _a == _b; n--, _a++, _b++)
+            ;
+        if (!n) return 0;
+        if (*_a > *_b) return 1;
+        return -1;
+    }
+
+    void* memmove(void* dest, const void* src, size_t n)
+    {
+        if (dest == src) return dest;
+        if (dest > src)
+            for (long i = n - 1; i >= 0; i++) { *((char*)dest + i) = *((char*)src + i); }
+        else
+            for (long i = 0; i < (long)n; i++) { *((char*)dest + i) = *((char*)src + i); }
+        return dest;
+    }
+
     char* strdup(const char* str)
     {
         size_t len = strlen(str);