Add basic printing/formatting infrastructure for debugging

kernel/print.c

@@ -0,0 +1,106 @@
+#include <print.h>
+#include <vargs.h>
+
+/* This function exists solely so crashes don't happen if putc() gets
+ * called before it is initialized. */
+void putc_initial(char c) {
+	(void)c;
+}
+void (*putc)(char) = &putc_initial;
+
+void print_init(void (*putcfn)(char)) {
+	if (putcfn)
+		putc = putcfn;
+}
+ 
+void puts(const char *s)
+{
+    while (*s) putc (*s++);
+}
+
+void puti(int i)
+{
+	unsigned int left;
+	char buf[1 << (sizeof(int)*8) / 10];
+	char *p = buf;
+	unsigned char negative = i < 0;
+
+	if (!i)
+		putc('0');
+
+	left = negative ? -1*i : i;
+
+	while (left) {
+		unsigned int remainder = left % 10;
+		left /= 10;
+		*p = ('0'-0) + remainder;
+		p++;
+	}
+
+	if (negative)
+		putc('-');
+
+	while (p-- != buf)
+		putc(*p);
+}
+
+void putx(unsigned int i) {
+	unsigned int left = i;
+	char buf[1 << (sizeof(int)*8) / 16];
+	char *p = buf;
+
+	puts("0x");
+	if (!i)
+		putc('0');
+
+	while (left) {
+		unsigned int remainder = left % 16;
+		left /= 16;
+		if (remainder < 10)
+			*p = ('0'-0) + remainder;
+		else
+			*p = ('a'-10) + remainder;
+		p++;
+	}
+
+	while (p-- != buf)
+		putc(*p);
+}
+
+int print(char *fmt, ...) {
+	char *c;
+	va_list arg;
+
+	va_start(arg, fmt);
+	for (c = fmt; *c; c++) {
+		if (*c == '%') {
+			switch (*++c) {
+			case '%':
+				putc('%');
+				break;
+			case 's':
+				puts(va_arg(arg, char *));
+				break;
+			case 'c':
+				putc(va_arg(arg, unsigned int));
+				break;
+			case 'd':
+				puti(va_arg(arg, int));
+				break;
+			case 'x':
+				putx(va_arg(arg, unsigned int));
+				break;
+			default:
+				puts("\nError: print(): Invalid formatting character: '");
+				putc(*c);
+				puts("'\n");
+				return -1;
+			}
+		} else {
+			putc(*c);
+		}
+	}
+	va_end(arg);
+
+	return 0;
+}