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1 Korn Shell 93 Bit Manipulation Finnbarr P. Murphy When programmers think about bitwise manipulation, they usually think about using C or C++ to solve their problem since both programming languages provide a rich set of features which make it easy to perform bitwise manipulation. However it is possible to just as easily perform such operations using the ksh93 shell. This post will explain what bitwise manipulation and number conversion facilities are available in ksh93 and provide some hopefully useful utilities and examples. Many programmers are unaware that ksh93 has builtin support for different numeral radices (AKA arithmetic bases) as shown in the following example. $ print $(( )) 30 $ print $(( 2# )) 22 $ print $(( 2#10 + 4#20 )) 10 $ where base 2 is denoted by 2#, base 4 by #4 and so on. The general case syntax is [base#]n where base is a decimal number between 2 and 36 representing the arithmetic base and n is a number in that base. You can mix and match bases within expressions. As you would expect, the default base, i.e. if [base#] is omitted, is decimal(10). Here is an example of how to convert decimal 255 to base 2, base 8 and base 16 respectively using the typeset command. $ typeset -i2 a=255 $ echo $a 2# $ typeset -i8 a=255 $ echo $a 8#377 $ typeset -i16 a=255 $ echo $a 16#ff $ Note that ksh93 displays the base prefix before each number unless it is a decimal number, i.e. base 10. The bitwise manipulation operators in ksh93 are AND, OR, XOR, SHIFT LEFT and SHIFT RIGHT. There are no SHIFT ROTATE or COMPLEMENT operators. The following is the list of supported bitwise operators in decreasing order of precedence which, by the way, is the same as in the C programming language. <> Bitwise shift left, shift right & Bitwise AND ^ Bitwise XOR Bitwise OR Copyright Finnbarr P. Murphy. All rights reserved. 1/6

2 The following shell script includes both logical and bitwise operators together with the expected output for each statement. Notice the difference in output between a logical and bitwise operator. integer -i2 a=5 integer -i2 b=6 # expected output 1 print $(( a < b )) # expected output 0 print $(( a > b )) # expected output 3 print $(( a ^ b )) # expected output 4 print $(( a & b )) # expected output 1 print $(( a && b )) # expected output 7 print $(( a b )) # expected output 1 print $(( a b )) A useful feature of bitwise operators is that by using the shift left and shift right bitwise operators you can mimic multiplication or division by 2 or a power of 2. $ x=4 $ print $((x < 8 $ print $(( x < 16 $ print $(( x >> 1 )) 2 $ print $(( x >> 2 )) 1 Here is a fairly simple shell script which uses numeric base conversion and bitwise operators to calculate the network and broadcast addresses for a given IP address and subnet mask.\ typeset -i2 mask=255 [[ $#!= 2 ]] && { echo "Usage: $0 ipaddress subnetmask" exit 1 } SaveIFS=$IFS IFS=. typeset -a IParr=($1) typeset -a NMarr=($2) IFS=$SaveIFS typeset -i2 ip1=${iparr[0]} typeset -i2 ip2=${iparr[1]} typeset -i2 ip3=${iparr[2]} typeset -i2 ip4=${iparr[3]} typeset -i2 nm1=${nmarr[0]} typeset -i2 nm2=${nmarr[1]} typeset -i2 nm3=${nmarr[2]} typeset -i2 nm4=${nmarr[3]} echo echo " IP Address: $1" echo " Subnet Mask: $2" echo " Network Address: $((ip1 & nm1)).$((ip2 & nm2)).$((ip3 & nm3)).$((ip4 & amp; nm4))" echo "Broadcast Address: $((ip1 (mask ^ nm1))).$((ip2 (mask ^ nm2))).$((ip3 (mask ^ nm3))).$(( ip4 (mask ^ nm4)))" Copyright Finnbarr P. Murphy. All rights reserved. 2/6

3 echo exit 0 Some sample output for this script. $./calculate-address IP Address: Subnet Mask: Network Address: Broadcast Address: $./calculate-address IP Address: Subnet Mask: Network Address: Broadcast Address: The next example calculates the network and broadcast addresses for a Classless Inter-Domain Routing (CIDR) compliant IP address. Note the use of the shift right operator in calculating the network mask. [[ $#!= 1 ]] && { echo "Usage: $0 ipaddress/netmask" exit 1 } SaveIFS=$IFS IFS="./" typeset -a IParr=($1) IFS=$SaveIFS typeset -i2 ip1=${iparr[0]} typeset -i2 ip2=${iparr[1]} typeset -i2 ip3=${iparr[2]} typeset -i2 ip4=${iparr[3]} typeset -i2 cidr=${iparr[4]} typeset -i2 nm1=0 nm2=0 nm3=0 nm4=0 typeset -i quad=$(( cidr / 8 )) sigbits=$(( cidr % 8 )) if (( sigbits!= 0 )); then slot=$(( ( 256 >> $sigbits ) )) fi for (( i=1; i < 5; i++ )) nameref nm=nm${i} if (( quad!= 0 )); then nm=255 (( --quad )) elif (( quad == 0 )); then nm=slot break fi ne typeset -i2 mask=255 print print " IP Address: $((ip1)).$((ip2)).$((ip3)).$((ip4))" print " CIDR Netmask Mask: $((nm1)).$((nm2)).$((nm3)).$((nm4))" print " CIDR Network (Route): $((ip1 & nm1)).$((ip2 & nm2)).$((ip3 & nm3)).$(( ip4 & nm4))" print " Broadcast Address: $((ip1 (mask ^ nm1))).$((ip2 (mask ^ nm2))).$((ip3 (ma sk ^ nm3))).$((ip4 (mask ^ n m4)))" Copyright Finnbarr P. Murphy. All rights reserved. 3/6

4 print exit 0 Sample output: $./calculate-address " /18" IP Address: CIDR Network Mask: CIDR Network (Route): Broadcast Address: For my example, suppose you are given a hexadecimal string 3AF9:3B01 and you want to expand that string to produce a list of all the values between 3AF9 and 3B01. The wrinkle is that you want all letters in the hexadecimal numbers to be uppercased. x=3af9:3b01 typeset -i16 a=0x${x%:*} typeset -i16 b=0x${x#*:} typeset -u c for (( ; a <= b; a++ )) c=${a:3} echo "$c" ne Here is the output: $./hexlist 3AF9 3AFA 3AFB 3AFC 3AFD 3AFE 3AFF 3B00 3B01 Here is another interesting example of using bit arithmetic to solve a problem. In this particular case, the user wanted to have a shell script which accepted a 32-bit hexadecimal number as input and assigns consecutive blocks of 4 bits of the equivalent binary number to each of 8 variables. integer -i2 mask=16#f integer -i2 v0 v1 v2 v3 v4 v5 v6 v7 read hn?"enter a 32-bit hex decimal number: " integer -i2 in=16#$hn for ((i=0; i < 8; i++)) nameref var=v${i} var=$(( ((in << (i*4)) & mask) >> 28 )) ne printf "% d\n" $in printf "%04.0.2d %04.0.2d %04.0.2d %04.0.2d %04.0.2d %04.0.2d %04.0.2d %04.0.2d\n" \ $v0 $v1 $v2 $v3 $v4 $v5 $v6 $v Copyright Finnbarr P. Murphy. All rights reserved. 4/6

5 Note the use of a third specifier with %d. In ksh93, each of the integral format specifiers can have a third modifier after width and precision that specifies the base of the conversion from 2 to 64. In addition the use of the # modifier as the third specifier will cause base# to be prepended to the value. Here is sample output for this script: $./hexblock Enter a 32-bit hex decimal number: abcdabcd $./hexblock Enter a 32-bit hex decimal number: AFC Suppose instead that you wanted to store the individual bits in an array. Here is one way to this is: read num?"enter binary 32 bit number: " integer -i2 a=2#$num integer -i2 mask=2# typeset -ui barray=( ) for (( i=0; i < 32; i++, mask=$(( mask << 1)) )) nameref var=barray[$i] (( $mask & $a )) && var=1 ne # how to test the array values if (( ${barray[0]} )) then echo "barray[0] is 1" else echo "barray[0] is 0" fi This example calculates the binary and decimal equivalent of an IP address: [[ $#!= 1 ]] && { echo "Usage: $0 ipaddress" exit 1 } SaveIFS=$IFS IFS="." typeset -a IParr=($1) IFS=$SaveIFS typeset -i2 ip1=${iparr[0]} typeset -i2 ip2=${iparr[1]} typeset -i2 ip3=${iparr[2]} typeset -i2 ip4=${iparr[3]} typeset -ui2 d=$(( (ip1 << 24) (ip2 << 16) (ip3 << 8) ip4 )) print "Inputted IP$ address: $((ip1)).$((ip2)).$((ip3)).$((ip4))" print " Binary equivalent: $d" print " Decimal equivalent: $((d))" exit Copyright Finnbarr P. Murphy. All rights reserved. 5/6

6 Here is sample output: $./example Inputted IP$ address: Binary equivalent: 2# Decimal equivalent: Finally, I would be amiss if I did not point out that both the bash and zsh shells also provide a full set of bitwise operators and support number base conversion Copyright Finnbarr P. Murphy. All rights reserved. 6/6