2019/day5.c

   1 #define _GNU_SOURCE 1
   2 #include <stdio.h>
   3 #include <string.h>
   4 #include <stdlib.h>
   5 #include <stdarg.h>
   6 #include <stdbool.h>
   7 #include <math.h>
   8
   9 #define LIMIT 2000
  10 static int a[LIMIT];
  11 static int len;
  12 static int pc;
  13
  14 static int do_debug = -1;
  15 static void
  16 debug(const char *fmt, ...) {
  17   va_list ap;
  18   if (do_debug < 0)
  19     do_debug = !!getenv("DEBUG");
  20   if (do_debug > 0) {
  21     va_start(ap, fmt);
  22     vfprintf(stderr, fmt, ap);
  23     va_end(ap);
  24   }
  25 }
  26
  27 static void
  28 dump(void) {
  29   if (!do_debug)
  30     return;
  31   for (int i = 0; i < len; i++)
  32     debug("%d,", a[i]);
  33   debug("\n");
  34 }
  35
  36 static void __attribute__((noreturn))
  37 crash(const char *msg) {
  38   printf("invalid program, pc=%d: %s\n", pc, msg);
  39   exit(1);
  40 }
  41
  42 static int
  43 get(int param) {
  44   int op = a[pc];
  45   int scale = pow(10, param + 1);
  46   int mode = (op / scale) % 10;
  47   int value;
  48
  49   debug("get mode=%d\n", mode);
  50   if (pc + param > len)
  51     crash("program too short for opcode");
  52   value = a[pc + param];
  53   switch (mode) {
  54   case 0:
  55     if (value > len || value < 0)
  56       crash("in position mode, param beyond end of program");
  57     return a[value];
  58   case 1:
  59     return value;
  60   default:
  61     crash("unexpected mode");
  62   }
  63 }
  64
  65 static void
  66 put(int param, int value) {
  67   int op = a[pc];
  68   int scale = pow(10, param + 1);
  69   int mode = (op / scale) % 10;
  70   int offset;
  71
  72   debug("put mode=%d\n", mode);
  73   if (pc + param > len)
  74     crash("program too short for opcode");
  75   offset = a[pc + param];
  76   switch (mode) {
  77   case 0:
  78     if (offset > len)
  79       crash("in position mode, param beyond end of program");
  80     a[offset] = value;
  81     return;
  82   default:
  83     crash("unexpected mode");
  84   }
  85 }
  86
  87 int
  88 main(int argc, char **argv) {
  89   int i, count = 0, jump;
  90   bool done = false;
  91   int reads = 0, input = 1;
  92
  93   if (argc > 1)
  94     if (!(stdin = freopen(argv[1], "r", stdin))) {
  95       perror("failure");
  96       exit(2);
  97     }
  98
  99   while (scanf("%d%*[,\n]", &i) == 1) {
 100     a[len++] = i;
 101     if (len > LIMIT - 3) {
 102       printf("recompile with larger LIMIT\n");
 103       exit(2);
 104     }
 105   }
 106   printf("Read %u slots\n", len);
 107   dump();
 108
 109   if (argc > 2)
 110     input = atoi(argv[2]);
 111
 112   while (!done) {
 113     count++;
 114     debug("executing %d,%d,%d,%d\n", a[pc], a[pc+1], a[pc+2], a[pc+3]);
 115     if (pc > len || pc < 0)
 116       crash("program ran out of bounds");
 117     switch (a[pc] % 100) {
 118     case 1:
 119       put(3, get(1) + get(2));
 120       jump = 4;
 121       break;
 122     case 2:
 123       put(3, get(1) * get(2));
 124       jump = 4;
 125       break;
 126     case 3:
 127       if (++reads != 1)
 128         crash("too many reads");
 129       put(1, input);
 130       jump = 2;
 131       break;
 132     case 4:
 133       printf("%d\n", get(1));
 134       jump = 2;
 135       break;
 136     case 5:
 137       if (get(1)) {
 138         pc = get(2);
 139         jump = 0;
 140       } else
 141         jump = 3;
 142       break;
 143     case 6:
 144       if (!get(1)) {
 145         pc = get(2);
 146         jump = 0;
 147       } else
 148         jump = 3;
 149       break;
 150     case 7:
 151       put(3, get(1) < get(2));
 152       jump = 4;
 153       break;
 154     case 8:
 155       put(3, get(1) == get(2));
 156       jump = 4;
 157       break;
 158     case 99:
 159       debug("halting\n");
 160       done = true;
 161       jump = 1;
 162       break;
 163     default:
 164       crash("unexpected opcode");
 165     }
 166     pc += jump;
 167     dump();
 168   }
 169   printf("after %d opcodes, slot 0 holds %d\n", count, a[0]);
 170   dump();
 171   return 0;
 172 }