#!/bin/sh
# add $2 to $1 and return
[ -z "${1##*.*}" -o -z "${2##*.*}" ] && { # if float # dylanaraps/pure-sh-bible#check-if-a-number-is-a-float 
  # modified to check $1 & $2
  if [ ! -z "${1##*.*}" ]; then
    set -- "${1}.0" "$2"; d="${1#*.}"; d2="${2#*.}"
    until [ "${#d}" -eq "${#d2}" ]; do
      set -- "${1}0" "$2"
      d="${1#*.}"
    done
  elif [ ! -z "${2##*.*}" ]; then
    set -- "$1" "${2}.0"; d="${2#*.}"; d2="${1#*.}"
    until [ "${#d}" -eq "${#d2}" ]; do
      set -- "$1" "${2}0"
      d="${2#*.}"
    done
  fi # if $1/$2 is not a float; convert to float
  until [ "${#1}" -ge "${#2}" ]; do
    set -- "0$1" "$2"
  done
  until [ "${#2}" -ge "${#1}" ]; do
    set -- "$1" "0$2"
  done
  #echo "$1 $2"
  f1="${1##*.}"; f2="${2##*.}" # whole is ${1%.$f1} # dot required
  # eq is $1+$2 -- $f1 + $f2 -- then add $1 & $2
  w1="${1%.$f1}"; w2="${2%.$f2}"
  until [ "${w1#0}" = "$w1" ]; do
    w1="${w1#0}"
  done
  until [ "${w2#0}" = "$w2" ]; do
    w2="${w2#0}"
  done # dash has issues when numbers have leading 0's
  # zsh,bash,etc don't need this at all
  wo="$((${w1#0}+${w2#0}))" # whole digit, this is preset and not redeclared
  # this is because we may need to carry
  while [ "$f1" ]; do
    while [ "$f2" ]; do
      next2="${f2#?}"; next1="${f1#?}"
      [ "$((${f1%$next1} + ${f2%$next2}))" -gt 9 ] && {
        oo="$o"; [ "$o" ] && {
          : $((oo+=1))
        } || : $((wo+=1))
        o="$((${f1%$next1} + ${f2%$next2}))"; o="${o#?}"; o="$oo$o"; unset oo # unset to save ram
      } || o="$o$((${f1%$next1} + ${f2%$next2}))"
      f2="$next2"; f1="${next1}" 
    done
  done
  echo "$wo.${o:-0}"
} || { # if not just do basic addition
  echo $(($1+$2))
}