Meta/Linus: How much of the very original version from Linus is still there?

diff --git a/Linus b/Linus
new file mode 100755 (executable)
index 0000000..8cbcd18
--- /dev/null
+++ b/Linus
@@ -0,0 +1,69 @@
+#!/bin/sh
+# How much of the very original version from Linus survive?
+
+_x40='[0-9a-f][0-9a-f][0-9a-f][0-9a-f][0-9a-f]'
+_x40="$_x40$_x40$_x40$_x40$_x40$_x40$_x40$_x40"
+
+initial=$(git rev-parse --verify e83c5163316f89bfbde7d9ab23ca2e25604af290) &&
+this=$(git rev-parse --verify ${1-HEAD}^0) || exit
+
+tmp="/var/tmp/Linus.$$"
+trap 'rm -f "$tmp".*' 0
+
+# We blame each file in the initial revision pretending as if it is a
+# direct descendant of the given version, and also pretend that the
+# latter is a root commit.  This way, lines in the initial revision
+# that survived to the other version can be identified (they will be
+# attributed to the other version).
+graft="$tmp.graft" &&
+{
+       echo "$initial $this"
+       echo "$this"
+} >"$graft" || exit
+
+opts='-C -C -C -w'
+
+show () {
+       s=$1 t=$2 n=$3
+       p=$(($s * 100 / $t))
+       c=$(($s * 10000 / $t - $p * 100))
+       printf "%12d %12d %s (%d.%02d%%)\n" $s $t $n $p $c
+}
+
+git ls-tree -r "$initial" |
+while read mode type sha1 name
+do
+       git blame $opts --porcelain -S "$graft" "$initial" -- "$name" |
+       sed -ne "s/^\($_x40\) .*/\1/p" |
+       sort |
+       uniq -c | {
+               # There are only two commits in the fake history, so
+               # there will be at most two output from the above.
+               read cnt1 commit1
+               read cnt2 commit2
+               if test -z "$commit2"
+               then
+                       cnt2=0
+               fi
+               if test "$initial" != "$commit1"
+               then
+                       cnt_surviving=$cnt1
+               else
+                       cnt_surviving=$cnt2
+               fi
+               cnt_total=$(( $cnt1 + $cnt2 ))
+               echo "$cnt_surviving $cnt_total $name"
+       }
+done | {
+       total=0
+       surviving=0
+       printf "%12s %12s %s (survival%%)\n" surviving original path
+       while read s t n
+       do
+               total=$(( $total + $t )) surviving=$(( $surviving + $s ))
+               # printf "%12d %12d %s\n" $s $t $n
+               show $s $t $n
+       done
+       # printf "%12d %12d %s\n" $surviving $total Total
+       show $surviving $total Total
+}