Added libc functions

common.c

@@ -0,0 +1,122 @@
+#include "common.h"
+
+void putchar(char c);
+
+size_t align_up(size_t value, size_t align)
+{
+    /* To align means to compute the smallest value which is greater than a
+     * given number and that is an exact multiple of another specified
+     * number */
+    size_t remainder = value % align;
+    if (remainder == 0)
+        return value;
+
+    return value + (align - remainder);
+}
+
+size_t is_aligned(size_t value, size_t align)
+{
+    return value % align == 0;
+}
+
+void *memcpy(void *dst, const void *src, size_t n)
+{
+    uint8_t *d = (uint8_t*)dst;
+    const uint8_t *s = (uint8_t*)src;
+    while (n--) {
+        *d++ = *s++;
+    }
+    return dst;
+}
+
+void *memset(void *buf, char c, size_t n)
+{
+    uint8_t *p = (uint8_t*)buf;
+    while (n--) {
+        *p++ = c;
+    }
+    return buf;
+}
+
+char *strcpy(char *dst, const char *src)
+{
+    char *d = dst;
+    while (*src != '\0') {
+        *d++ = *src++;
+    }
+    *d = '\0';
+    return dst;
+}
+
+int strcmp(const char *s1, const char *s2)
+{
+    while (*s1 && *s2 && *s1 == *s2) {
+        s1++;
+        s2++;
+    }
+    return *((unsigned char *)s1) - *((unsigned char *)s2);
+}
+
+void printf(const char *fmt, ...)
+{
+    va_list args;
+    va_start(args, fmt);
+    while (*fmt != '\0') {
+        if (*fmt != '%') {
+            putchar(*fmt);
+            fmt++;
+        } else {
+            fmt++; // consume %
+            switch (*fmt) {
+            case '\0':
+                putchar('%');
+                goto end;
+            case '%':
+                putchar('%');
+                break;
+            case 's':
+                const char *s = va_arg(args, const char*);
+                while (*s != '\0') {
+                    putchar(*s);
+                    s++;
+                }
+                break;
+            case 'd':
+                int num = va_arg(args, int);
+                unsigned int magnitude = num;
+                unsigned int power = 1;
+                if (num < 0) {
+                    putchar('-');
+                    magnitude = -magnitude;
+                }
+
+                while ((magnitude / power) > 9) {
+                    power *= 10;
+                }
+
+                while (power > 0) {
+                    putchar('0' + (magnitude / power));
+                    magnitude %= power;
+                    power /= 10;
+                }
+                break;
+            case 'x':
+                unsigned int hex = va_arg(args, unsigned int);
+                putchar('0');
+                putchar('x');
+                for (int i = 7; i >= 0; i--) {
+                    unsigned int nibble = (hex >> (4 * i)) & 0xf;
+                    putchar("0123456789abcdef"[nibble]);
+                }
+                break;
+            }
+
+            fmt++; // consume modifier
+        }
+    }
+
+end:
+    va_end(args);
+
+    return;
+}