diff --git a/day3/mkinput b/day3/mkinput-old
similarity index 100%
rename from day3/mkinput
rename to day3/mkinput-old
diff --git a/day3/mkinput.c b/day3/mkinput.c
new file mode 100644
index 0000000..260d186
--- /dev/null
+++ b/day3/mkinput.c
@@ -0,0 +1,152 @@
+//! -pipe -std=gnu17 -O3 -msse -fwhole-program -flto -fno-strict-aliasing -Wall -Wstrict-aliasing -Werror -Wl,-flto -Wl,-O3 -o
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <fcntl.h>
+#include <stdbool.h>
+#include <errno.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+
+#define expect(expr, msg) ({ __auto_type _expect__expr = (expr); \
+			if(__builtin_expect(!_expect__expr, 0)) { perror("Fatal error: `" #expr "` failed: " msg); exit(1); } \
+			_expect__expr; })
+
+union openfd {
+	struct {
+		off_t len;
+		FILE* file;
+	} buf;
+	struct {
+		off_t len;
+		int fd;
+	} raw;
+};
+
+typedef struct mappedfd {
+	int fd;
+	size_t len;
+
+	uintptr_t origin;
+} mmap_t;
+
+inline static void* map_ptr(const mmap_t* map)
+{
+	return (void*)map->origin;
+}
+
+bool filesz(int fd, off_t* restrict size)
+{
+	if(fd<0) return false;
+	struct stat st;
+	if(fstat(fd, &st)) return false;
+	*size = st.st_size;
+	return true;
+}
+
+bool bopen(const char* name, const char* perm, union openfd* restrict file)
+{
+	FILE* f = fopen(name, perm);
+	if(!f) return false;
+	if(!filesz(fileno(f), &file->buf.len)) return (fclose(f), false);
+	file->buf.file = f;	
+	return true;
+}
+
+bool ropen(const char* name, int perm, union openfd* restrict file)
+{
+	int fd = open(name, perm, 0);
+	if(fd<0) return false;
+	if(!filesz(fd, &file->raw.len)) return (close(fd), false);
+	file->raw.fd = fd;
+	return true;
+}
+
+bool btor(union openfd* restrict file)
+{
+	if(fflush(file->buf.file)) return false;
+	int fd = fileno(file->buf.file);
+
+	file->raw.len = file->buf.len;
+	file->raw.fd = fd;
+	
+	return true;
+}
+
+inline bool rclose(union openfd file)
+{
+	return close(file.raw.fd) != 0;
+}
+
+inline void bclose(union openfd file)
+{
+	fclose(file.buf.file);
+}
+
+bool map_raw(union openfd* restrict file, mmap_t* restrict map)
+{
+	void* origin = mmap(NULL, (size_t)file->raw.len, PROT_READ, MAP_SHARED, file->raw.fd, 0);
+	if(origin == MAP_FAILED) return false;
+	*map = (mmap_t){ 
+		.fd = file->raw.fd,
+		.len = (size_t)file->raw.len,
+		.origin = (uintptr_t)origin,
+	};
+	file->raw.fd = -1;
+	return true;
+}
+
+bool map_clone(const mmap_t* from, mmap_t* restrict to)
+{
+	void* origin = mmap((void*)from->origin, from->len, PROT_READ|PROT_WRITE, MAP_PRIVATE, from->fd, 0);
+	if(origin == MAP_FAILED) return false;
+	*to = (mmap_t){
+		.fd = -1,
+		.len = from->len,
+		.origin = (uintptr_t)origin,
+	};
+	return true;
+}
+
+void map_close(mmap_t map)
+{
+	munmap((void*)map.origin, map.len);
+	if(map.fd >= 0) close(map.fd);
+}
+
+inline bool map_buf(union openfd* restrict file, mmap_t* restrict map)
+{
+	if(!btor(file)) return false;
+	return map_raw(file, map);
+}
+
+bool process(const mmap_t* io)
+{
+	char* input =  map_ptr(io);
+	size_t size = io->len;
+
+	
+}
+
+int main(int argc, char** argv)
+{
+	if(argc < 1) return 1;
+	int rc = 0;
+	
+	union openfd input;
+	expect(ropen(argv[1], O_RDONLY, &input), "couldn't open input file");
+
+	mmap_t read;
+	expect(map_raw(&input, &read), "failed to map file");
+	mmap_t write;
+	expect(map_clone(&read, &write), "failed to clone page");
+	
+	if(!process(&write)) rc = (perror("failed to process"), 1);
+
+	map_close(write);
+	map_close(read);
+	return rc;
+}
+