implement basic string functions (memset, memcpy, etc)

Makefile

@@ -1,5 +1,5 @@
 # Define the object files
-OBJS = bin/boot.o bin/kernel.o bin/idt.o bin/isr.o bin/screen.o bin/utils.o
+OBJS = bin/boot.o bin/kernel.o bin/idt.o bin/isr.o bin/screen.o bin/utils.o bin/string.o
 
 # Define the compiler and assembler
 CC = gcc
@@ -39,6 +39,9 @@ bin/idt.o: src/idt.c
 bin/utils.o: src/utils.c
 	$(CC) $(CFLAGS) -c $< -o $@
 
+bin/string.o: src/string.c
+	$(CC) $(CFLAGS) -c $< -o $@
+
 clean:
 	rm -rf bin/
 	rm -f $(OUTPUT)

include/string.h

@@ -0,0 +1,12 @@
+#ifndef STRING_H
+#define STRING_H
+
+#include <stddef.h>
+
+int memcmp(const void*, const void*, size_t);
+void* memcpy(void* __restrict, const void* __restrict, size_t);
+void* memmove(void*, const void*, size_t);
+void* memset(void*, int, size_t);
+size_t strlen(const char*);
+
+#endif

src/screen.c

@@ -1,5 +1,6 @@
 // screen.c
 #include "../include/screen.h"
+#include "../include/string.h"
 
 static size_t terminal_row;
 static size_t terminal_column;
@@ -16,14 +17,6 @@ inline uint16_t vga_entry(unsigned char uc, uint8_t color)
         return (uint16_t) uc | (uint16_t) color << 8;
 }
 
-size_t strlen(const char* str) 
-{
-        size_t len = 0;
-        while (str[len])
-                len++;
-        return len;
-}
-
 void terminal_initialize(void) 
 {
         terminal_row = 0;

src/string.c

@@ -0,0 +1,50 @@
+#include "../include/string.h"
+
+int memcmp(const void* aptr, const void* bptr, size_t size)
+{
+	const unsigned char* a = (const unsigned char*) aptr;
+	const unsigned char* b = (const unsigned char*) bptr;
+	for (size_t i = 0; i < size; i++) {
+		if (a[i] < b[i])
+			return -1;
+		else if (b[i] < a[i])
+			return 1;
+	}
+	return 0;
+}
+
+void* memcpy(void* restrict dstptr, const void* restrict srcptr, size_t size) {
+	unsigned char* dst = (unsigned char*) dstptr;
+	const unsigned char* src = (const unsigned char*) srcptr;
+	for (size_t i = 0; i < size; i++)
+		dst[i] = src[i];
+	return dstptr;
+}
+
+void* memmove(void* dstptr, const void* srcptr, size_t size) {
+	unsigned char* dst = (unsigned char*) dstptr;
+	const unsigned char* src = (const unsigned char*) srcptr;
+	if (dst < src) {
+		for (size_t i = 0; i < size; i++)
+			dst[i] = src[i];
+	} else {
+		for (size_t i = size; i != 0; i--)
+			dst[i-1] = src[i-1];
+	}
+	return dstptr;
+}
+
+void* memset(void* bufptr, int value, size_t size) {
+	unsigned char* buf = (unsigned char*) bufptr;
+	for (size_t i = 0; i < size; i++)
+		buf[i] = (unsigned char) value;
+	return bufptr;
+}
+
+size_t strlen(const char* str)
+{
+	size_t len = 0;
+	while(str[len])
+		len++;
+	return len;
+}