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