autoreconf breaks shell functions in configure.ac

[Yuri]

I added this function to configure.ac:

log2() {
  x=0
  y=$(($1>>1))
  while [ $y -gt 0 ]; do
    x=$((x+1))
    y=$((y>>1))
  done
  echo $x
}


After autoreconf, this function looks like this:

log2() {
  x=0
  y=$(($1>>1))
  while  $y -gt 0 ; do
    x=$((x+1))
    y=$((y>>1))
  done
  echo $x
}


The brackets are dropped around the argument of 'while'.

This alters the outcome of this function. Now, instead of computing the 
log2(x) function, it breaks: x.sh: 3: not found


I believe, this is a major bug that the body of the shell function is 
altered.


autoconf-2.69_1 on FreeBSD 11.1


Yuri