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# Copyright (c) 2017 The NetBSD Foundation, Inc.
# All rights reserved.
#
# This code is derived from software contributed to The NetBSD Foundation
# by Johnny C. Lam.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
# 1. Redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer.
# 2. Redistributions in binary form must reproduce the above copyright
# notice, this list of conditions and the following disclaimer in the
# documentation and/or other materials provided with the distribution.
#
# THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
# ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
# TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
# PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
# BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
# POSSIBILITY OF SUCH DAMAGE.
#
# NAME
# random.subr -- generate random number (badly)
#
# SYNOPSIS
# task_random [-i [<seed>]]
#
# echo $RANDOM
#
# DESCRIPTION
# The task_random function sets RANDOM to a random integer from the
# range 0..32767. It should always be called before using the $RANDOM
# value. The seed can be explicitly set in order to ensure a
# deterministic sequence of $RANDOM values.
#
# The options are as follows:
#
# -i <seed>
# Explicitly initialize with a new seed. If the seed is not
# given, then a new seed is chosen based on the current time.
#
# If the shell already has a built-in implementation for $RANDOM,
# then the task_random function simply returns 0.
#
# RETURN VALUES
# The task_random function returns 0 on success, and >0 if an error
# occurs.
#
# ENVIRONMENT
# The following variables are used if they are set:
#
# AWK The name or path to the awk(1) utility.
#
# DATE The name or path to the date(1) utility.
#
# EXAMPLE
# for i in 1 2 3 4 5; do
# task_random && echo $RANDOM
# done
#
# BUGS
# The pseudorandom number sequence will eventually enter a cycle of
# length 209, so task_random should periodically reseeded if a long
# sequence of random numbers is needed.
#
__task_random__="yes"
__task_random_init__="_random_init"
task_random()
{
: ${AWK:=awk}
: ${DATE:=date}
local randomseed=
local arg
local OPTIND=1
while getopts ":i:" arg "$@"; do
case $arg in
i) randomseed=${OPTARG} ;;
*) return 127 ;;
esac
done
shift $(( ${OPTIND} - 1 ))
[ $# -eq 0 ] || return 127
if [ -n "$__task_random_exists__" ]; then
#
# If the shell already has a $RANDOM implementation, then
# setting RANDOM to a value initializes the seed for the
# random sequence.
#
[ -z "$randomseed" ] || RANDOM=$randomseed
return 0
fi
local randomseed_init=
if [ -n "$randomseed" ]; then
#
# This function was called with an explicit seed, so the
# next time this function is called without an argument,
# a new seed must be generated.
#
randomseed_init="yes"
elif [ -z "$randomseed_init" ]; then
#
# If a random seed has not been initialized, then set the
# seed to the time prepended with 1 and appended with a
# process PID. This ensures the it is a number not
# beginning with zero and that it differs between multiple
# invocations of this function within a short span of time.
#
randomseed_init="yes"
local randomseed_pid
( : ) & randomseed_pid=$!
wait $randomseed_pid
randomseed=$( ${DATE} +"1%H%M%S$randomseed_pid" )
else
# A random seed was previously generated, so just use
# $RANDOM as the next seed.
#
randomseed=$RANDOM
fi
# Use awk's rand() to generate random numbers; however, the PRNG
# for awk needs to be seeded appropriately between invocations.
#
RANDOM=$( ${AWK} -v SEED=$randomseed -v RAND_MAX=32768 \
'BEGIN { srand(SEED); print int( RAND_MAX * rand() ) } ')
}
_random_init()
{
# Test for the presence of a $RANDOM implementation when this file is
# loaded, so that entropy is not wasted.
#
case $RANDOM in
$RANDOM)
__task_random_exists__= ;;
*) __task_random_exists__="yes" ;;
esac
}
# Static variable for whether a builtin $RANDOM exists.
__task_random_exists__=
|
