radix

#!/bin/bash
help() { cat <</help
Convert a number to any radix (arithmetic base) between 2 and 64 (inclusive)
Usage: $self [-][INPUT_RADIX#]NUMBER [OUTPUT_RADIX]
       $self md5[:STRING] [OUTPUT_RADIX]

-               The negative sign goes *before* the INPUT_RADIX, not after
INPUT_RADIX     The input radix is any integer between 2 and 64 (default = 10)
NUMBER          Any integer. Digits run 0-9 then a-z then A-Z then @ then _
                Must be 64-bit (-$max to $max)
OUTPUT_RADIX    The output radix is any integer between 2 and 64
                If INPUT_RADIX is 10, default = 36. Otherwise default = 10.
md5             Use a truncated MD5 checksum of STRING (or else standard input)
STRING          A string to checksum. No trailing linebreak is added.

Examples:
  $self 123               # \`ya\` (defaults to input/output radices of 10/36)
  $self -805854694382 32  # \`-negative\`
  $self -32\\#negative     # \`-805854694382\` (defaults to output radix 10)
  $self "64#1F_@rS" 36    # \`testme\`
  $self "md5:hey Joe" 64  # \`6ZGm5WN3VNv\` (THIS IS NOT A PASSWORD GENERATOR!)

/help
  version
}

version() {
  echo "Part of misc-scripts: https://github.com/adamhotep/misc-scripts"
  echo "radix 0.1.20241124.0 copyright 2024+ by Adam Katz, GPL v3+"
  exit
}

we_have() { command -v "$@" >/dev/null; }	# true if the command exists

die() { echo "$self: $*" >&2; exit 2; } 	# report error and exit

isNaN() { ! [ "${1#-}" -le $max ] 2>/dev/null; }	# cannot use [[ ... ]]

vet_radix() {
  r="radix (arithmetic base) \`$1\`"
  if isNaN "$1"; then
    die "Invalid number for $r"
  elif (( 2 > $1 || $1 > 64 )); then
    die "Out of bounds $r is not 2-64"
  fi
}

self="${0##*/}"

if [[ $1 == -- ]]; then
  shift
elif [[ $# == 0 ]]; then
  help |grep -A1 ^Usage
  exit
fi

iradix=10 	# input radix (updated later if specified in the number)
number="$1"	# input number, which may specify an input radix
oradix="$2"	# output radix
digits="0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ@_"
# -9223372036854775808 is 64-bit, but it had issues, so it is forbidden
max=9223372036854775807
out_of_bounds="Number must be between -$max and $max"

case $number in
  ( -h* | --help* | help )	help ;;
  ( -v* | -V | ver | version )	version ;;
  ( md5* )
    if ! we_have md5sum; then
      if we_have busybox && busybox |grep -Fwq md5sum; then
        md5sum() { busybox md5sum "$@"; }
      elif we_have md5; then
        md5sum() { md5 "$@"; }
      else
        die "Cannot locate md5 checksummer"
      fi
    fi
    case $number in
      ( md5 )	number="$(cat |md5sum)" ;;
      ( md5:* )	number="$(printf %s "${number#md5:}" |md5sum)" ;;
      ( * )	die 'MD5 must be invoked as either `md5` or `md5:STRING`' ;;
    esac
    tmp="${number#????????????????}"
    number="16#${number%$tmp}"
    ;;
esac

if isNaN "$number"; then
  : "NUMBER is not an integer. Determine its safety then convert to an integer"
  if [[ $number != *\#* ]]; then
    if [[ ${number#-} != *[^0-9]* ]]; then
      die "$out_of_bounds"
    else
      die "Invalid number \`$1\` (no input radix specified? see \`--help\`)"
    fi
  fi
  abs="${number#-}"
  iradix="${abs%%#*}"
  vet_radix "$iradix"
  case ${abs#$iradix#} in
    ( '' | *[!0-9a-zA-Z@_]* )	die "Invalid number \`$number\`" ;;
  esac
  : "convert \`$number\` to an integer or else exit after bash arithmetic error"
  (( (number += 0) || number == 0 )) || exit 2
  : "number converted from <$1> to <$number>"
fi

case $iradix:$oradix in
  ( 10: )	oradix=36 ;;
  ( *: )	oradix=10 ;;
esac

vet_radix "$oradix"

if (( number < 0 )); then
  sign='-'
  number="${number#-}"
else
  sign=''
fi

if isNaN "$number"; then
  die "$out_of_bounds"
fi

out=""
while (( number != 0 )); do
  out="${digits:(( number % oradix )):1}${out}"
  (( number /= oradix ))
done

echo "$sign${out:-$number}"