[SDK:CRT] Implement more string routines

SDK/CRT/STRING/str.c

@@ -43,3 +43,87 @@ strnlen (
 
     return len - sizeof(char);
 }
+
+int
+strcmp (
+    const char* s1,
+    const char* s2
+    )
+
+{
+    while (*s1 == *s2) {
+        if (*s1 == '\0') {
+            return 0;
+        }
+
+        s1++;
+        s2++;
+    }
+
+    return *(unsigned char *)s1 - *(unsigned char*)s2;
+}
+
+int
+strncmp (
+    const char* s1,
+    const char* s2,
+    size_t n
+    )
+
+{
+    while (n > 0) {
+        if (*s1 != *s2) {
+            return *(unsigned char *)s1 - *(unsigned char*)s2;
+        }
+
+        if (*s1 == '\0') {
+            return 0;
+        }
+
+        n--;
+        s1++;
+        s2++;
+    }
+
+    return 0;
+}
+
+char *
+strchr (
+    const char *s,
+    int c
+    )
+
+{
+    while (*s != (char)c) {
+        if (!*s) {
+            return NULL;
+        }
+
+        s++;
+    }
+
+    return (char *)s;
+}
+
+char *
+strstr (
+    const char *haystack,
+    const char *needle
+    )
+
+{
+    const char *ptr = haystack;
+
+    if (!*needle) {
+        return (char *)haystack;
+    }
+
+    while ((ptr = strchr(ptr, *needle)) != NULL) {
+        if (strcmp(ptr, needle) == 0) {
+            return (char *)ptr;
+        }
+    }
+
+    return NULL;
+}