From c8ab406749124d2e762ad5cf53963070113afd0f Mon Sep 17 00:00:00 2001
From: Tom Ryder <tom@sanctum.geek.nz>
Date: Wed, 5 Apr 2017 20:06:39 +1200
Subject: Apply runtime shebanging to POSIX shell

---
 games/rndn.sh | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100644 games/rndn.sh

(limited to 'games/rndn.sh')

diff --git a/games/rndn.sh b/games/rndn.sh
new file mode 100644
index 00000000..18c34218
--- /dev/null
+++ b/games/rndn.sh
@@ -0,0 +1,43 @@
+#!/bin/sh
+# Esoteric random number generator
+
+# Single optional argument is a random seed, otherwise use rnds(1df)
+s=${1:-"$(rnds)"}
+
+# Validate s
+case $s in
+    *[!0-9]*)
+        printf >&2 'rndn: Seed must be non-negative integer\n'
+        exit 2
+        ;;
+esac
+
+# Helper functions
+t() {
+    printf %u "$1" | cut -c -"$2"
+}
+l() {
+    printf %u "$1" | wc -c
+}
+c() {
+    printf %u "$1" | cut -c "$2"
+}
+
+# Apply algorithm; you are not expected to understand this
+s=$(t "$((s + 10))" 32) i=1 t=0
+while [ "$i" -le "$(l "$s")" ] ; do
+    d=$(c "$s" "$i")
+    t=$((t + d)) i=$((i + 1))
+done
+p=$((s - t))
+while [ "$(l "$p")" -gt 1 ] ; do
+    j=1 q=0
+    while [ "$j" -le "$(l "$p")" ] ; do
+        d=$(c "$p" "$j")
+        q=$((q + d)) j=$((j + 1))
+    done
+    p=$q
+done
+
+# Print result
+printf '%u\n' "$p"
-- 
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