2 files changed, 77 insertions, 0 deletions
diff --git a/src/shared/printf.c b/src/shared/printf.c
new file mode 100644
index 0000000..496d5b8
--- /dev/null
+++ b/src/shared/printf.c
@@ -0,0 +1,71 @@
+#include <shared/mem.h>
+#include <shared/printf.h>
+
+int __printf_internal(const char *fmt, va_list argp,
+		void (*back)(void*, const char*, size_t), void *back_arg)
+{
+	const char *seg = fmt; // beginning of the current segment
+	int total = 0;
+
+	for (;;) {
+		char c = *fmt++;
+		switch (c) {
+			case '\0':
+				back(back_arg, seg, fmt - seg - 1);
+				return total + (fmt - seg - 1);
+
+			case '%':
+				back(back_arg, seg, fmt - seg - 1);
+				total += fmt - seg - 1;
+				size_t pad_len = 0;
+
+				c = *fmt++;
+				while (1) {
+					switch (c) {
+						case '0':
+							pad_len = *fmt++ - '0'; // can skip over the null byte, idc
+							break;
+						default:
+							goto modifier_break;
+					}
+					c = *fmt++;
+				}
+modifier_break:
+				switch (c) {
+					case 'c':
+						char c = va_arg(argp, int);
+						back(back_arg, &c, 1);
+						total += 1;
+						break;
+
+					case 's':
+						const char *s = va_arg(argp, char*);
+						if (s) {
+							back(back_arg, s, strlen(s));
+							total += strlen(s);
+						}
+						break;
+
+					case 'x':
+						unsigned int n = va_arg(argp, int);
+						size_t i = 4; // nibbles * 4
+						while (n >> i && i < (sizeof(int) * 8))
+							i += 4;
+
+						if (i < pad_len * 4)
+							i = pad_len * 4;
+
+						while (i > 0) {
+							i -= 4;
+							char h = '0' + ((n >> i) & 0xf);
+							if (h > '9') h += 'a' - '9' - 1;
+							back(back_arg, &h, 1);
+							total++;
+						}
+						break;
+				}
+				seg = fmt;
+				break;
+		}
+	}
+}
diff --git a/src/shared/printf.h b/src/shared/printf.h
new file mode 100644
index 0000000..45fd358
--- /dev/null
+++ b/src/shared/printf.h
@@ -0,0 +1,6 @@
+#pragma once
+#include <stdarg.h>
+#include <stddef.h>
+
+int __printf_internal(const char *fmt, va_list argp,
+		void (*back)(void*, const char*, size_t), void *back_arg);