crc16-xmodem.sh

#!/bin/bash

# Computes the CRC16 - XMODEM (also known as ZMODEM or CRC-16/ACORN)
# rewritten to bash from C code found at: https://beebwiki.mdfs.net/CRC-16

declare -i poly=0x1021
declare -i init=0x0000

function crc16() {
    local input="$1"
    local -i crc=${init}
    local -i pos; for (( pos=0; pos<${#input}; pos++ )); do
        local ord; LC_CTYPE=C printf -v ord '%d' "'${input:pos:1}"
        crc=$(( crc ^ ( ord << 8 ) ))
        # shellcheck disable=SC2034
        for i in {0..7}; do
            crc=$(( crc << 1 ))
            (( crc & 0x10000 )) && crc=$(( ( crc ^ poly ) & 0xFFFF ))
        done
    done
    echo ${crc}
}

function crc16hex() {
    local -i crc; crc=$(crc16 "$1")
    printf '%04X\n' "${crc}"
}

function crc16mod16384() {
    local -i crc; crc=$(crc16 "$1")
    printf '%d\n' "$(( crc % 16384 ))"
}

crc16hex "$1"