Kernel: add memmem

kernel/include/std/string.h

@@ -13,6 +13,7 @@ int strncmp(const char* a, const char* b, size_t n);
 char* strncat(char* dest, const char* src, size_t n);
 
 char* strstr(char* haystack, const char* needle);
+void* memmem(void* haystack, size_t haystacklen, const void* needle, size_t needlelen);
 
 void* memcpy(void* dest, const void* src, size_t n);
 void* memset(void* dest, int c, size_t n);

kernel/src/std/string.cpp

@@ -87,20 +87,25 @@ char* strcat(char* dest, const char* src)
 
 char* strstr(char* haystack, const char* needle)
 {
-    size_t needle_size = strlen(needle);
-    size_t haystack_size = strlen(haystack);
-    while (*haystack)
+    return (char*)memmem(haystack, strlen(haystack), needle, strlen(needle));
+}
+
+void* memmem(void* haystack, size_t haystacklen, const void* needle, size_t needlelen)
+{
+    const char* hs = (const char*)haystack;
+    const char* nd = (const char*)needle;
+    while (haystacklen)
     {
-        if (*haystack == *needle)
+        if (*hs == *nd)
         {
-            if (needle_size <= haystack_size)
+            if (needlelen <= haystacklen)
             {
-                if (!strncmp(haystack, needle, needle_size)) return haystack;
+                if (!memcmp(hs, nd, needlelen)) return (void*)const_cast<char*>(hs);
             }
             else { return NULL; }
         }
-        haystack++;
-        haystack_size--;
+        hs++;
+        haystacklen--;
     }
     return NULL;
 }