decimal_calc

#!/usr/bin/env bash

# declare -r MY_PATH="$0"
readonly MY_PATH=$(realpath "$0")
MY_NAME=''
if [[ "$MY_PATH" =~ ^(.*)/([^/]+)$ ]]; then
	readonly MY_NAME="${BASH_REMATCH[2]}"
else
	readonly MY_NAME="$0"
fi
readonly MATCH_LINE='^[[:blank:]]*exit_error .*?'
exit_error() {
	line=$(grep -m 1 -n -E -e "$MATCH_LINE($1)" "$MY_PATH")
	if [[ "$line" =~ ^([[:digit:]]+) ]]; then
		line="${BASH_REMATCH[1]}: "
	else
		line=''
	fi
	echo "$MY_NAME: $line$*" 1>&2
	exit 1
}
declare -ri DEFAULT_COARSENESS=100
declare -r DEFAULT_DECIMAL='.'
show_help() {
	cat << __EOF__
Print the result of the given division operation with the specified precision, trimming trailing zeros and rounding excess.

Usage:	$0 NUMERATOR DENOMINATOR [COARSENESS SEPARATOR]
	or:	$0 [-c COARSENESS] [-d SEPARATOR] NUMERATOR DENOMINATOR
	or:	$0 --help
	or:	$0 --version

Options:
	-c, --coarseness COARSENESS: precision. Defaults to $DEFAULT_COARSENESS.
	-d, --decimal SEPARATOR: the fractional separator. Defaults to $DEFAULT_DECIMAL
	-h, --help: Shows this help text.
	-v, --version: Shows version info.
__EOF__
}
show_version() {
	cat << __EOF__
$0 3.0.0

Copyright (C) 2025 Justin Morris
__EOF__
}
declare -i numerator=0; unset numerator
declare -i denominator=0; unset denominator
declare coarseInput # ="${coarseInput:-100}"
declare separator='.'
while [[ -n "${1+x}" ]]; do
	case "$1" in
		(-h | --help)
			show_help
			exit
			;;
		(-v | --version)
			show_version
			exit
			;;
		(-c | --coarseness)
			shift
			coarseInput="$1"
			shift
			;;
		(-d | --decimal)
			shift
			separator="$1"
			shift
			;;
		(*)
			if [[ -n "${numerator+x}" ]]; then
				if [[ -n "${denominator+x}" ]]; then
					if [[ -n "${coarseInput+x}" ]]; then
						exit 1
					else
						coarseInput="$1"
					fi
				else
					((denominator = $1))
				fi
			else
				((numerator = $1))
			fi
			shift
			;;
	esac
done

declare -ir numerator denominator
if ((denominator == 0)); then
	exit_error 'Divide by zero error: ' "$numerator / $denominator"
fi
if ((numerator == 0)); then
	echo -n '0'
	exit
fi
declare -i n=0 d=0
declare sign=''
# Can't be 0 here; simplifies checks
if ((numerator > 0 && denominator > 0)); then
	declare -r n=$numerator d=$denominator sign=''
elif ((numerator < 0 && denominator < 0)); then
	declare -r n=$((numerator * -1)) d=$((denominator * -1)) sign=''
else
	if ((numerator < 0)); then
		declare -r n=$((numerator * -1)) d=$denominator sign='-'
	else
		declare -r d=$((denominator * -1)) n=$numerator sign='-'
	fi
fi
declare -i whole=n/d
# If there's no remainder
if (( numerator % denominator == 0 )); then
	echo -n "$sign$whole"
	exit
fi
declare -r coarseInput="${coarseInput:-$DEFAULT_COARSENESS}"
declare -ir decimalDigits="${#coarseInput}"
declare -ir coarseness="$((10 ** decimalDigits))"
if ((coarseness==1)); then
	echo -n "$sign$whole"
	exit
fi
declare -i whole_count=0; declare +i whole; ((whole_count=${#whole})); declare -i whole
declare -i l_intermediate=0; ((l_intermediate=n * coarseness)); 
if ((l_intermediate < n)); then
	exit_error 'OVERFLOW ' "($whole $l_intermediate) ($numerator / $denominator)"
fi
((l_intermediate /= d)); 
if ((l_intermediate==0)); then
	echo -n "$sign$whole"
	exit
fi
declare +i l_intermediate
while [[ "${l_intermediate: -1}" == '0' ]] && ((${#l_intermediate} > whole_count)); do
	l_intermediate="${l_intermediate:0:-1}"
done
if ((${#l_intermediate} == whole_count)); then
	echo -n "$sign$whole";
	exit
elif ((${#l_intermediate} < whole_count)); then
	exit_error 'UNDEFINED BEHAVIOR (too small a fraction?): ' "$numerator / $denominator"
elif ((${#l_intermediate} > whole_count )); then
	if ((${#l_intermediate} - whole_count >= decimalDigits)); then
		((t_last=${l_intermediate: -1}))
		if ((t_last<5)); then
			declare +i l_intermediate="${l_intermediate:0:-1}"
		else
			((t_l=${l_intermediate:0:-1} + 1))
			declare +i l_intermediate="${l_intermediate:0:-1}"
			declare +i t_l
			if (( ${#t_l} > ${#l_intermediate} )); then
				((whole_count++))
				whole="${t_l:0:whole_count}"
			fi
			declare +i l_intermediate="$t_l"
			unset t_l
		fi
		while [[ "${l_intermediate: -1}" == '0' ]] && ((${#l_intermediate} > whole_count)); do
			l_intermediate="${l_intermediate:0:-1}"
		done
	fi
	if ((${#l_intermediate} == whole_count)); then
		echo -n "$sign$l_intermediate"
		exit
	else
		if ((whole_count > 1 || whole != 0)); then
			echo -n "$sign$whole$separator${l_intermediate:$whole_count}"
		else
			echo -n "$sign$separator${l_intermediate}"
		fi
		exit
	fi
fi
exit_error 'Should not be able to reach this point: ' "$numerator / $denominator"