day 4

day1.c

@@ -1,4 +1,65 @@
-#include "lib.h"
+#include <stdlib.h>
+#include <stdcountof.h>
+#include <stdint.h>
+#include <string.h>
+
+#define SYS_write 1
+#define SYS_exit_group 231
+
+#define STDOUT_FILENO 1
+
+static
+void write(uint64_t fileno, void *buffer, size_t len) {
+    uint64_t a,d;
+    asm volatile("syscall"
+        :"=a"(a),"=d"(d):"a"(SYS_write),"D"(fileno),"S"(buffer),"d"(len):"memory");
+}
+
+[[noreturn]] static
+void exit_group() {
+    asm volatile(
+        "syscall\n"
+        "ud2"
+        ::"a"(SYS_exit_group),"D"(0));
+    for (;;);
+}
+
+#define xstr(s) str(s)
+#define str(s) #s
+
+static
+void print_many_char(size_t len, char chars[len]) {
+    write(STDOUT_FILENO, chars, len);
+}
+
+#define print(string) print_many_char(sizeof(string)-1, string)
+
+static
+void printd(unsigned long v) {
+    if (!v) {
+        print("0");
+        return;
+    }
+    char buf[32];
+    char *p = buf+32;
+    unsigned count = 0;
+    while (v) {
+        p--;
+        *p = '0' + (v % 10);
+        v /= 10;
+        count++;
+    }
+    write(STDOUT_FILENO, p, count);
+}
+
+static
+unsigned grabnum(const char *s, const char **end) {
+    unsigned r = 0;
+    for (; *s >= '0' && *s <= '9'; s++)
+        r = r * 10 + (*s - '0');
+    *end = s;
+    return r;
+}
 
 #define DBG 1
 
@@ -74,7 +135,7 @@ unsigned do_part2(size_t src_len, const char src[src_len]) {
     return count;
 }
 
-void _start() {
+void run() {
 #if RUN_TEST1
     print("PART 1 TEST: ");
     if (unsigned long v = do_part1(countof(test), test); v != TEST1_EXPECT) {
@@ -109,5 +170,5 @@ void _start() {
     print("\n");
 #endif
 
-    syscall(SYS_exit_group, 0);
+    exit_group();
 }