day16/decoder.sh

   1 #!/bin/bash
   2
   3 set -u
   4
   5 filename=${1:-p1_16.txt}
   6 debug=${2:-0}
   7
   8 exec 3<"${filename}"
   9
  10 declare -A hex_to_binary=( [0]="0000" [1]="0001" [2]="0010" [3]="0011" [4]="0100" [5]="0101" [6]="0110" [7]="0111" [8]="1000" [9]="1001" [A]="1010" [B]="1011" [C]="1100" [D]="1101" [E]="1110" [F]="1111" )
  11
  12 read -u 3 hex_string
  13
  14 declare -g __packets=""
  15 for (( a=0; a<${#hex_string}; a++ )); do
  16     __packets+=${hex_to_binary[${hex_string:$a:1}]}
  17 done
  18
  19 declare -g __versions_total=0
  20
  21 declare __packet_offset=0
  22
  23 if [ $debug == "0"  ]; then
  24     echo_verbose() { true; }
  25 else
  26     echo_verbose() { echo "$@" >&2; }
  27 fi
  28
  29 parse_version() {
  30     declare -g __packet_version=$((2#${__packets:$__packet_offset:3}))
  31     ((__packet_offset+=3))
  32     echo_verbose "Packet version: $__packet_version"
  33 }
  34
  35 parse_type() {
  36     declare -g __packet_type=$((2#${__packets:$__packet_offset:3}))
  37     ((__packet_offset+=3))
  38     echo_verbose "Packet type: $__packet_type"
  39 }
  40
  41 parse_literal() {
  42     local keep_going=${__packets:$__packet_offset:1}
  43     local binary_value=""
  44     ((__packet_offset+=1))
  45     while [ $keep_going -eq 1 ]; do
  46         binary_value+=${__packets:$__packet_offset:4}
  47         ((__packet_offset+=4))
  48         keep_going=${__packets:$__packet_offset:1}
  49         ((__packet_offset+=1))
  50     done
  51     # if we're here, we're on to the last group
  52     binary_value+=${__packets:$__packet_offset:4}
  53     ((__packet_offset+=4))
  54     declare -g __packet_literal=$((2#$binary_value))
  55     echo_verbose "Packet literal: $__packet_literal"
  56 }
  57
  58 parse_operator() {
  59     local len_type=$((2#${__packets:$__packet_offset:1}))
  60     ((__packet_offset+=1))
  61
  62     case $len_type in
  63         0)
  64             __packets_length=$((2#${__packets:$__packet_offset:15}))
  65             ((__packet_offset+=15))
  66             ;;
  67         1)
  68             __packets_count=$((2#${__packets:$__packet_offset:11}))
  69             ((__packet_offset+=11))
  70             ;;
  71     esac
  72 }
  73
  74 parse_packets() {
  75     # we'll first need the version and the type, so grab those
  76     local pversion
  77     local ptype
  78
  79     while [ $__packet_offset -lt ${#__packets} ]; do
  80         parse_version
  81         parse_type
  82         version=$__packet_version
  83         ptype=$__packet_type
  84
  85         ((__versions_total+=$version))
  86
  87         echo_verbose "Remaining: ${__packets:$__packet_offset}"
  88
  89         case $ptype in
  90             4)
  91                 parse_literal
  92                 ;;
  93             *)
  94                 parse_operator
  95                 ;;
  96         esac
  97
  98         if [ $(($__packet_offset+7)) -ge ${#__packets} ]; then
  99             break
 100         fi
 101     done
 102 }
 103
 104 parse_packets
 105
 106 echo "Total: $__versions_total"