initial commit

bash/grains/grains.sh

@@ -0,0 +1,65 @@
+#!/usr/bin/env bash
+#
+# V1: initial version
+#
+# Note: untested on 32 bits and big-endian architectures
+
+shopt -s extglob
+
+# set to mask to enable logs. 0: none, 255: all
+(( debug=2#00000000 ))
+#(( debug=2#00001111 ))
+# $1: log level (mask), then strings to display.
+debug () {
+    (( debug & $1 )) && shift && echo Line ${BASH_LINENO[0]}: "${@}" >&2
+}
+
+die () {
+    echo "${@}" >&2
+    exit 1
+}
+usage() {
+    die "Error: invalid input"
+}
+
+# we want 1 arg only, "total" or digits only.
+(($# !=1 )) || \
+    [[ "$1" != +([[:digit:]]) ]] && \
+    [[ "$1" != "total" ]] && usage
+
+arg="${1##+(0)}"                        # we strip leading zeroes if any
+debug 1 arg="$arg"
+
+case "$arg" in
+    total)
+        # formula to calculate a geometric series of common ratio r and first
+        # term f, that is: S=f + fr² + fr³ ... + frⁿ
+        # is: S = f * [ (1 - rⁿ⁺¹) / (1 - r) ]
+        #
+        # for r=2 and f=1, it becomes:
+        # S = 1 * (1 - 2ⁿ⁺¹) / -1 = 2ⁿ⁺¹ - 1
+        # So here, as total does not accept an argument, such as "last square",
+        # the value is 2⁶⁴-1.
+        # Notes: (2**64) is 0 on 64 bits, but better not to use this property.
+        #        We could also directly output the value, as it is a constant.
+        printf -v result "%llu" $(( 2**64 - 1 ))
+        ;;
+    *)                                  # always digits here
+        debug 2 "digits=args"
+        (( arg < 1 || arg > 64 )) && usage
+        printf -v result "%llu" $(( 2**(arg-1) ))
+        ;;
+esac
+
+echo "$result"
+
+exit 0
+
+# emacs/vim settings.
+# Local Variables:
+# sh-basic-offset: 4
+# indent-tabs-mode: nil
+# comment-column: 40
+# fill-column: 80
+# End:
+# vim: set tabstop=4 expandtab: