commit: 711f1c52ca266d9bad207b13e83ce740c780f2db
Author: Kerin Millar <kfm <AT> plushkava <DOT> net>
AuthorDate: Tue Oct 14 06:09:22 2025 +0000
Commit: Sam James <sam <AT> gentoo <DOT> org>
CommitDate: Tue Oct 14 12:59:09 2025 +0000
URL:
https://gitweb.gentoo.org/proj/gentoo-functions.git/commit/?id=711f1c52
Simplify the portable srandom() implementation
Presently, there are two implementations of the srandom() function, one
of which is intended for bash while the other is intended for sh. The
latter implementation employs a pattern to search for 8 consecutive hex
digits in the entropy pool, where the first is between 0 and 7.
Simplify matters by unconditionally consuming 8 hex digits from the pool
before employing a case statement that clamps the first digit, provided
that it is greater than 0x7. The resulting code is more pleasant to read
and maintain. What's more, it improves the performance in dash by
approximately 10%.
Signed-off-by: Kerin Millar <kfm <AT> plushkava.net>
Signed-off-by: Sam James <sam <AT> gentoo.org>
functions.sh | 52 +++++++++++++++++++++++++---------------------------
1 file changed, 25 insertions(+), 27 deletions(-)
diff --git a/functions.sh b/functions.sh
index 02ee297..cff6f5a 100644
--- a/functions.sh
+++ b/functions.sh
@@ -581,49 +581,47 @@ quote_args()
#
# shellcheck disable=3028
if [ "${BASH_VERSINFO-0}" -ge 5 ] && [ "${SRANDOM}" != "${SRANDOM}" ]; then
- # Take advantage of the SRANDOM variable, as introduced by bash 5.1.
srandom()
{
printf '%d\n' "$(( SRANDOM >> 1 ))"
}
elif [ -c /dev/urandom ]; then
- # Employ a method which entails searching for 8 consecutive hex digits,
- # where the first is between 0 and 7.
-
genfun_int32_pat='[0-7][[:xdigit:]][[:xdigit:]][[:xdigit:]][[:xdigit:]][[:xdigit:]][[:xdigit:]][[:xdigit:]]'
unset -v genfun_entropy
srandom()
{
- local hex i slice
+ local hex slice
- # If the shell has forked, or if it cannot be determined
- # whether it has done so, populate the pool with 64 bytes worth
- # of fresh entropy.
- if ! _update_pid; then
+ if [ "${#genfun_entropy}" -lt 8 ]; then
+ # Not enough entropy is left in the pool.
+ _collect_entropy
+ elif ! _update_pid; then
+ # Fork detection is unavailable.
_collect_entropy
elif ! eval "test \"\${genfun_pool_${genfun_pid}+set}\""; then
+ # A newly forked shell has been detected.
_collect_entropy &&
eval "genfun_pool_${genfun_pid}=1"
fi || return
- for i in 1 2 3; do
- # shellcheck disable=2295
- slice=${genfun_entropy%${genfun_int32_pat}*}
- if [ "${#slice}" -ne "${#genfun_entropy}" ]; then
- hex=${genfun_entropy#"$slice"}
- genfun_entropy=${genfun_entropy%"$hex"}
- while [ "${#hex}" -gt 8 ]; do
- hex=${hex%?}
- done
- break
- elif [ "$i" -lt 3 ]; then
- # The pool does not contain a suitable
- # sequence. Refill it then try again.
- _collect_entropy
- else
- false
- fi
- done &&
+ # Consume 8 hex digits (32 bits) from the pool.
+ slice=${genfun_entropy%????????}
+ hex=${genfun_entropy#"$slice"}
+ genfun_entropy=${slice}
+
+ # Clamp to the desired range (0x7FFFFFFF at most).
+ case ${hex} in
+ 8*) hex=0${hex#?} ;;
+ 9*) hex=1${hex#?} ;;
+ a*) hex=2${hex#?} ;;
+ b*) hex=3${hex#?} ;;
+ c*) hex=4${hex#?} ;;
+ d*) hex=5${hex#?} ;;
+ e*) hex=6${hex#?} ;;
+ f*) hex=7${hex#?}
+ esac
+
+ # Print as decimal.
printf '%d\n' "0x${hex}"
}
else
