2016/advent12.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 int regs[4];
  10 char *program[50]; // sized based on pre-inspecting file
  11
  12 int
  13 get (const char *value)
  14 {
  15   if (isalpha(*value))
  16     return regs[*value - 'a'];
  17   return atoi (value);
  18 }
  19
  20 void
  21 set (const char *reg, int value)
  22 {
  23   regs[*reg - 'a'] = value;
  24 }
  25
  26 int main(int argc, char **argv)
  27 {
  28   int instr = 0;
  29   char buf[200]; // sized based on pre-inspecting file
  30   int nread = fread (buf, 1, sizeof buf, stdin);
  31   char *p = buf;
  32   while (p < buf + nread) {
  33     program[instr++] = p;
  34     p = strchr (p, '\n');
  35     *p++ = '\0';
  36   }
  37   printf ("program consists of %d instructions\n", instr);
  38   unsigned int pc = 0;
  39   regs[2] = 1;
  40   int count = 0;
  41   while (pc < instr) {
  42     char arg1[10], arg2[10];
  43     count++;
  44     sscanf (program[pc], "%*s %9s %9s", arg1, arg2);
  45     switch (program[pc][0]) {
  46     case 'c': // cpy
  47       set (arg2, get (arg1));
  48       pc++;
  49       break;
  50     case 'i': // inc
  51       set (arg1, get (arg1) + 1);
  52       pc++;
  53       break;
  54     case 'd': // dec
  55       set (arg1, get (arg1) - 1);
  56       pc++;
  57       break;
  58     case 'j': // jnz
  59       if (get (arg1))
  60         pc += atoi (arg2);
  61       else
  62         pc++;
  63       break;
  64     default:
  65       return 1;
  66     }
  67   }
  68   printf ("after %d operations, final content of register a: %d\n",
  69           count, regs[0]);
  70   return 0;
  71 }