#Bit-Banging in Bash (with od and rm)

# Adler32 checksum of a file with Bash, rm, and od.
# Rick rickfordictator.com Hohensee August 2023
# E is the checksum. Android .dex files use Adler32.
# not checked much, but it is clearly doing binary data.

decimalbytes ()
{ od -An -v -t d1 -w1 $1 >> decimal.out
}

Subadler () { # < decimal.out
A=1 B=0
while read
do
let A=$(($A+$REPLY))
let A=$(($A&0xffffffff))
let B=$B+$A
let B=$(($B&0xffffffff))
done
}

Adler32 () {
decimalbytes $1

Subadler < decimal.out
rm decimal.out
C=$((A%65521))
D=$((B%65521))
echo "C =" $C " D = " $D
E=$(((D<<16)|C))
echo $E

}

On Friday, August 25, 2023 at 11:00:45 PM UTC-4, Rick Hohensee wrote:
> #Bit-Banging in Bash (with od and rm)
>
> # Adler32 checksum of a file with Bash, rm, and od.
> # Rick rickfordictator.com Hohensee August 2023
> # E is the checksum. Android .dex files use Adler32.
> # not checked much, but it is clearly doing binary data.
>
> decimalbytes ()
> {
> od -An -v -t d1 -w1 $1 >> decimal.out
> }
>
>
> Subadler () { # < decimal.out
> A=1 B=0
> while read
> do
> let A=$(($A+$REPLY))
> let A=$(($A&0xffffffff))
> let B=$B+$A
> let B=$(($B&0xffffffff))
> done
> }
>
>
> Adler32 () {
> decimalbytes $1
>
> Subadler < decimal.out
> rm decimal.out
> C=$((A%65521))
> D=$((B%65521))
> echo "C =" $C " D = " $D
> E=$(((D<<16)|C))

should be E=$(((C<<16)|D))
and the low two bytes still don't match an online example, but the high two bytes do