srand32.zsh

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