Improves userland libraries

common/inc/altc/altio.h

@@ -1,8 +1,10 @@
 #pragma once
+#include <stddef.h>
 
 int alt_getchar(void);
 int alt_putchar(char c);
 int alt_putstr(const char *str);
 int alt_puts(const char *str);
 int alt_gets(char *str);
 int alt_printf(const char *fmt, ...);
+int alt_snprintf(char *restrict s, size_t n, char *restrict fmt, ...);

common/src/altc/snprintf.c

@@ -0,0 +1,71 @@
+#include <stdarg.h>
+#include <stddef.h>
+
+static char *write_hex(char *restrict dst, const char *end,
+		       unsigned long long val)
+{
+	if (!val && dst != end) {
+		*(dst++) = '0';
+	} else if (dst != end) {
+		int i = 0;
+		char buf[16];
+		while (val) {
+			int tmp = val & 0xF;
+			buf[i++] = tmp < 10 ? ('0' + tmp) : 'A' + (tmp - 10);
+			val >>= 4;
+		}
+		while (i > 0 && dst != end)
+			*(dst++) = buf[--i];
+	}
+	return dst;
+}
+
+static char *write_str(char *restrict dst, const char *end, char *restrict src)
+{
+	while (dst != end && *src != '\0')
+		*(dst++) = *(src++);
+	return dst;
+}
+
+static char *write_char(char *restrict dst, const char *end, char c)
+{
+	if (dst != end)
+		*(dst++) = c;
+	return dst;
+}
+
+int alt_snprintf(char *restrict str, size_t size, const char *restrict fmt, ...)
+{
+	va_list args;
+	char *s = str;
+	const char *end = str + size - 1;
+	va_start(args, fmt);
+	while (*fmt != '\0' && s != end) {
+		if (*(fmt++) != '%') {
+			s = write_char(s, end, *(fmt - 1));
+			continue;
+		}
+		switch (*(fmt++)) {
+		case '%':
+			s = write_char(s, end, '%');
+			break;
+		case 'c':
+			s = write_char(s, end, va_arg(args, int));
+			break;
+		case 's':
+			s = write_str(s, end, va_arg(args, char *));
+			break;
+		case 'x':
+			s = write_hex(s, end, va_arg(args, unsigned int));
+			break;
+		case 'X':
+			s = write_hex(s, end, va_arg(args, unsigned long long));
+			break;
+		case '\0':
+			break;
+		}
+	}
+	*s = '\0';
+	va_end(args);
+	return s - str;
+}