Added some string.h functions

src/kernel/string.c

@@ -1,4 +1,5 @@
 #include "string.h"
+#include "stdint.h"
 
 // Source: http://www.strudel.org.uk/itoa/
 char* itoa(uint32_t val, uint8_t base) {
@@ -17,3 +18,42 @@ char* itoa(uint32_t val, uint8_t base) {
     return &buf[i + 1];
 }
 
+// Some implementations taken from https://en.wikibooks.org/wiki/C_Programming/String_manipulation
+char* strcat(char* str1, const char* str2) {
+    char* s = str1;
+    while (*s != '\0') { s++; }
+    strcpy(s, str2);
+    return str1;
+}
+
+char* strchr(const char* str, char c) {
+    const char* s = str;
+    while (*s != '\0' && *s != c) { s++; }
+    return (*s == c) ? (char*)s : NULL;
+}
+
+int strcmp(const char* str1, const char* str2) {
+    while (*str1 != '\0' && *str1 == *str2) {
+        str1++;
+        str2++;
+    }
+
+    uint8_t c1 = (*(uint8_t*)str1);
+    uint8_t c2 = (*(uint8_t*)str2);
+
+    return ((c1 < c2) ? -1 : (c1 > c2));
+}
+
+char* strcpy(char* str1, const char* str2) {
+    char* dst = str1;
+    const char* src = str2;
+    while ((*dst++ = *src++) != '\0');
+    return str1;
+}
+
+uint32_t strlen(const char* str) {
+    const char* p = str;
+    while (*++p != '\0');
+    return (uint32_t)(p - str);
+}
+