feat: added memchr, memcmp, memmv and realloc

srcs/ft_memchr.c

@@ -0,0 +1,35 @@
+#include <stddef.h>
+#include <stdint.h>
+
+void *ft_memchr(const void *s, int c, size_t n)
+{
+    const unsigned char *p = s;
+    unsigned char uc = (unsigned char)c;
+
+    while (n && ((uintptr_t)p % sizeof(size_t))) {
+        if (*p == uc)
+            return ((void *)p);
+        ++p;
+        --n;
+    }
+    size_t mask = 0;
+    for (size_t i = 0; i < sizeof(size_t); ++i)
+        mask |= (size_t)uc << (i * 8);
+
+    while (n >= sizeof(size_t)) {
+        size_t word = *(const size_t *)p;
+        size_t cmp = word ^ mask;
+        for (size_t i = 0; i < sizeof(size_t); ++i) {
+            if (((cmp >> (i * 8)) & 0xFF) == 0)
+                return ((void *)(p + i));
+        }
+        p += sizeof(size_t);
+        n -= sizeof(size_t);
+    }
+    while (n--) {
+        if (*p == uc)
+            return ((void *)p);
+        ++p;
+    }
+    return (NULL);
+}