look/bash/main3.sh

#!/bin/bash

add_byte() {
    local a=$1
    local b=$2

    if [ $a -lt 0 ]; then
        a=$((256 + a))
    fi

    if [ $b -lt 0 ]; then
        b=$((256 + b))
    fi

    local sum=$((a + b))

    sum=$((sum % 256))

    if [ $sum -gt 127 ]; then
        sum=$((sum - 256))
    fi

    echo $sum
}

add_word() {
    local a=$1
    local b=$2

    if [ $a -lt 0 ]; then
        a=$((65536 + a))
    fi

    if [ $b -lt 0 ]; then
        b=$((65536 + b))
    fi
    local sum=$((a + b))

    sum=$((sum % 65536))

    if [ $sum -gt 32767 ]; then
        sum=$((sum - 65536))
    fi

    echo $sum
}

result1=$(add_byte 79 -46)
echo "79 + (-46) = $result1"

result2=$(add_byte -97 96)
echo "-97 + 96 = $result2"

result3=$(add_word 12868 -1219)
echo "12868 + (-1219) = $result3"