calc

#!/bin/bash

#
# Wrapper around bc for easier use and nicer output.
#
# Author: Alex Van't Hof <alexvh@cs.columbia.edu>
# License: None, Public Domain
#

PRECISION=${PRECISION:-15} # Allow env based override of precision

usage() {
	cat << EOF
Usage: $(basename "$0") [OPTION]... [EQUATION]
Solve an equation.
    -d        output in decimal even if EQUATION contains hex numbers
    -h        output in hex even if EQUATION contains decimal numbers
    --help    display this text and exit

EQUATION may contain hex numbers so long as they are preceded by '0x'.
If EQUATION contains a hex number, the output will be in hex if -d is not given.
See \`man bc\` for legal EQUATION operators.

Default precision is 15 digits. It can be overidden by setting the \$PRECISION
environment variable.
EOF
}

TEMP=$(getopt -o dhs --long help -n calc -- "$@")
eval set -- "$TEMP"

force_dec=0
force_hex=0
while true; do
	case "$1" in
	--help) usage; exit 0 ;;
	-d) shift; force_dec=1 ;;
	-h) shift; force_hex=1 ;;
	--) shift; break ;;
	*) echo "getopt failed" >&2; exit 1 ;;
	esac
done

if [ $force_hex -eq 1 ] && [ $# -eq 0 ]; then
	# Assume user used -h as --help
	usage
	exit 0
fi

piped_input=
if [ ! -t 0 ]; then
	read piped_input
fi

equation="$piped_input $*"
hex_num=''
while [[ "$equation" =~ (0x[0-9a-fA-F]+) ]]; do
	hex_num=${BASH_REMATCH[0]}
	dec_repl=$(printf "%d\n" "$hex_num")
	equation=${equation/$hex_num/$dec_repl}
done

# bc can't handle fractional exponents so convert these to e(exp*l(base))
equation=$(echo "$equation" | sed -r 's/([0-9]+)\^([0-9]*\.[0-9]+|\([^\)]+\))/e(\2*l(\1))/g')

if [ "$PRECISION" -gt 15 ]; then
	# High precision hack (%g can only handle 15 digits)
	result=$(bc -l <<< "scale=$PRECISION; $equation" | tr -d '\n')
else
	result=$(bc -l <<< "scale=$PRECISION; $equation" | \
		 awk '{printf "%.'"$PRECISION"'g\n", $0}')
fi

if [[ $force_dec -eq 0 && -n "$hex_num" || $force_hex -eq 1 ]]; then
	# Output using same casing as given (or upper if mixed)
	[[ "$@" =~ [A-F] ]] && x="X" || x="x"
	printf "0x%$x\n" "$result"
else
	echo "$result"
fi