libc: Add strcmp() and strncmp()

libs/libc/include/string.h

@@ -50,6 +50,12 @@ extern "C"
     /* Concatenates at most max bytes of the string src into dest. */
     char* strncat(char* dest, const char* src, size_t max);
 
+    /* Compares strings a and b. You might prefer to use the safer strncmp function. */
+    int strcmp(const char* a, const char* b);
+
+    /* Compares at most max bytes of the strings a and b. */
+    int strncmp(const char* a, const char* b, size_t max);
+
     /* Returns the error string associated with the error number err. */
     char* strerror(int err);
 

libs/libc/src/string.cpp

@@ -81,6 +81,27 @@ extern "C"
         return dest;
     }
 
+    int strcmp(const char* a, const char* b)
+    {
+        while (*a && (*a == *b))
+        {
+            a++;
+            b++;
+        }
+        return *(const unsigned char*)a - *(const unsigned char*)b;
+    }
+
+    int strncmp(const char* a, const char* b, size_t max)
+    {
+        const char* base = a;
+        while (*a && (*a == *b) && (size_t)(a - base) < (max - 1))
+        {
+            a++;
+            b++;
+        }
+        return *(const unsigned char*)a - *(const unsigned char*)b;
+    }
+
     char* strcat(char* dest, const char* src)
     {
         size_t dest_len = strlen(dest);