// it is encoded in logical instructions with 3 bitfields
// N (1 bit) : R (6 bits) : S (6 bits), where
// N=1           -- period=64
// N=0, S=0xxxxx -- period=32
// N=0, S=10xxxx -- period=16
// N=0, S=110xxx -- period=8
// N=0, S=1110xx -- period=4
// N=0, S=11110x -- period=2
// R is the shift amount, low bits of S = n-1
func bitconEncode(x uint64, mode int) uint32 {
	if mode == 32 {

function append_or_replace_prefixed_line {
  local -r file="${1:-}"
  local -r prefix="${2:-}"
  local -r suffix="${3:-}"
  local -r dirname=$(dirname "${file}")
  local -r tmpfile=$(mktemp "${dirname}/filtered.XXXX")

  touch "${file}"
  awk -v pfx="${prefix}" 'substr($0,1,length(pfx)) != pfx { print }' "${file}" > "${tmpfile}"
  echo "${prefix}${suffix}" >> "${tmpfile}"
  mv "${tmpfile}" "${file}"
}