Calculate uniqueness of hostname hashes using SHA256 algorithm

hostname-hash-uniqueness.sh

#!/bin/bash
#
# Calculate uniqueness of hostname hashes using SHA256 algorithm
#

# hostname-0001, hostname-0002, hostname-0003...
HOSTNAME_BASE="hostname";

# % of unique hashes for 256 host names: 0.65625000000000000000
USED_NODES=256;         # used nodes
CUT_DIGITS='cut -c-2';  # max nodes: 2**8=256
for i in `seq 1 $USED_NODES`; do HOST=`printf "$HOSTNAME_BASE-%05d" $i`; echo -n $HOST | sha256sum | $CUT_DIGITS ; done > /tmp/hashlist.txt;
UNIQUE_HASHES=`cat /tmp/hashlist.txt | sort -u | wc -l`; echo $UNIQUE_HASHES / $USED_NODES | bc -l;

# % of unique hashes for 4096 host names: 0.62768554687500000000
USED_NODES=4096;        # used nodes
CUT_DIGITS='cut -c-3';  # max nodes: 2**12=4096
for i in `seq 1 $USED_NODES`; do HOST=`printf "$HOSTNAME_BASE-%05d" $i`; echo -n $HOST | sha256sum | $CUT_DIGITS ; done > /tmp/hashlist.txt;
UNIQUE_HASHES=`cat /tmp/hashlist.txt | sort -u | wc -l`; echo $UNIQUE_HASHES / $USED_NODES | bc -l;

# % of unique hashes for 65536 host names: 0.63201904296875000000
USED_NODES=65536;       # used nodes
CUT_DIGITS='cut -c-4';  # max nodes: 2**16=65536
for i in `seq 1 $USED_NODES`; do HOST=`printf "$HOSTNAME_BASE-%05d" $i`; echo -n $HOST | sha256sum | $CUT_DIGITS ; done > /tmp/hashlist.txt;
UNIQUE_HASHES=`cat /tmp/hashlist.txt | sort -u | wc -l`; echo $UNIQUE_HASHES / $USED_NODES | bc -l;