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@romkatv
Last active May 4, 2024 05:04
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srand32.zsh
# Returns a random 32-bit number.
# If /dev/urandom is cryptographically secure, so is srand32.
#
# If zsh is compiled with 64-bit number support, the result
# is non-negative. Otherwise it may be negative and the value
# is governed by the rules of unsigned-to-signed conversion in C.
#
# Examples:
#
# % print -r -- $(( srand32() ))
# 263510467
#
# % local -i x='srand32()'
# % typeset -p x
# typeset -i x=858148951
#
# Performance: ~30us per call.
#
# % time ( repeat 1000000 srand32 )
# user=19.95s system=6.95s cpu=99% total=26.934
#
# % uname -srm
# Linux 5.4.0-58-generic x86_64
#
# % grep 'model name' /proc/cpuinfo | head -1
# model name : AMD Ryzen 7 3700X 8-Core Processor
function srand32() {
emulate -L zsh -o no_multi_byte
local bytes
while (( $#bytes < 4 )); do
sysread -s$((4-$#bytes)) 'bytes[$#bytes+1]' </dev/urandom || return
done
local b1=$bytes[1] b2=$bytes[2] b3=$bytes[3] b4=$bytes[4]
return '#b1 << 24 | #b2 << 16 | #b3 << 8 | #b4'
}
functions -M srand32 0 0
zmodload zsh/system
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