2017/advent18.c

   1 #define _GNU_SOURCE 1
   2 #include <stdio.h>
   3 #include <string.h>
   4 #include <stdlib.h>
   5 #include <unistd.h>
   6 #include <stdbool.h>
   7 #include <ctype.h>
   8
   9 typedef struct state state;
  10 typedef struct elt elt;
  11 struct elt {
  12   long long v;
  13   elt *next;
  14 };
  15 struct state {
  16   long long regs[26];
  17   unsigned int pc;
  18   elt *head;
  19   elt *tail;
  20   int sent;
  21   int count;
  22 } states[2];
  23
  24 char *program[50]; // sized based on pre-inspecting file
  25 int instr;
  26
  27 long long
  28 get (state *s, const char *value)
  29 {
  30   if (isalpha(*value))
  31     return s->regs[*value - 'a'];
  32   return atoi (value);
  33 }
  34
  35 void
  36 set (state *s, const char *reg, long long value)
  37 {
  38   s->regs[*reg - 'a'] = value;
  39   if (getenv ("DEBUG"))
  40     printf (" %s=%lld\n", reg, value);
  41 }
  42
  43 bool
  44 run (state *s, int id)
  45 {
  46   elt *e;
  47   while (s->pc < instr) {
  48     char arg1[10], arg2[10];
  49     if (getenv ("DEBUG"))
  50       printf ("p%d instr %d at pc %d: %s\n", id, s->count, s->pc,
  51               program[s->pc]);
  52     sscanf (program[s->pc], "%*s %9s %9s", arg1, arg2);
  53     switch ((program[s->pc][0] << 8) + program[s->pc][1]) {
  54     case ('s' << 8) + 'n': // snd X
  55       e = malloc (sizeof *e);
  56       e->v = get (s, arg1);
  57       e->next = NULL;
  58       if (s->tail)
  59         s->tail->next = e;
  60       else
  61         s->head = e;
  62       s->tail = e;
  63       s->sent++;
  64       break;
  65     case ('s' << 8) + 'e': // set X Y
  66       set (s, arg1, get (s, arg2));
  67       break;
  68     case ('a' << 8) + 'd': // add X Y
  69       set (s, arg1, get (s, arg1) + get (s, arg2));
  70       break;
  71     case ('m' << 8) + 'u': // mul X Y
  72       set (s, arg1, get (s, arg1) * get (s, arg2));
  73       break;
  74     case ('m' << 8) + 'o': // mod X Y
  75       set (s, arg1, get (s, arg1) % get (s, arg2));
  76       break;
  77     case ('r' << 8) + 'c': // rcv X
  78       if (!states[!id].head)
  79         return true;
  80       e = states[!id].head;
  81       states[!id].head = e->next;
  82       if (!e->next)
  83         states[!id].tail = NULL;
  84       set (s, arg1, e->v);
  85       free (e);
  86       break;
  87     case ('j' << 8) + 'g': // jgz X Y
  88       if (get (s, arg1) > 0)
  89         s->pc += get (s, arg2) - 1;
  90       break;
  91     default:
  92       return 1;
  93     }
  94     s->count++;
  95     s->pc++;
  96   }
  97   return false;
  98 }
  99
 100 int main(int argc, char **argv)
 101 {
 102   char buf[400]; // sized based on pre-inspecting file
 103   int nread = fread (buf, 1, sizeof buf, stdin);
 104   char *p = buf;
 105   while (p < buf + nread) {
 106     program[instr++] = p;
 107     p = strchr (p, '\n');
 108     *p++ = '\0';
 109   }
 110   printf ("program consists of %d instructions\n", instr);
 111   states[1].regs['p' - 'a'] = 1;
 112   int swap = 0;
 113   while ((run (&states[0], 0) + run (&states[1], 1)) &&
 114          (states[0].head || states[1].head)) {
 115     swap++;
 116     printf ("%d+%d operations, %d swaps, %d+%d sent\n", states[0].count,
 117             states[1].count, swap, states[0].sent, states[1].sent);
 118   }
 119   printf ("after %d+%d operations and %d swaps, p1 sent %d times\n",
 120           states[0].count, states[1].count, swap, states[1].sent);
 121   return 0;
 122 }