78 lines
2.2 KiB
Sed
78 lines
2.2 KiB
Sed
# Increment base-10 number by 1
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#
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# Copyright (C) 2018 Mike Gerwitz
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#
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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#
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# This shows how to perform basic arithmetic on numbers using regular
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# expressions. The method is outlined below. It's easy to see that, for
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# any base-N number of M digits, we need NM regexes. For K such numbers, we
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# need NMK regexes. The more M or K we have, the more complex the regexes
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# become to handle the offsets. (The use of the `^' and `$' anchors alone
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# for replacements are only sufficient for M≤3 when K=1; what do we have to
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# do when M>3 to replace only the digits we are interested in?)
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#
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# It is possible to subtract using the same concept (see `base10-mul.sed').
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# Further, since we can implement addition and subtraction, we can also
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# implement multiplication and division.
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#
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# TO USE: Provide a 0-padded 3-digit base-10 number. Each time this script
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# is run, the number will be incremented by one. Exits with exit code 1 if
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# a non-3-digit-number is provided; and 2 once we cannot count any higher.
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##
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# Input must only be numbers
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/^[0-9]\{3\}$/!q1
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# Increment 1s (third character). If we overflow, represent the overflow as
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# an `A', which is then handled below.
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s/9$/A/
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s/8$/9/
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s/7$/8/
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s/6$/7/
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s/5$/6/
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s/4$/5/
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s/3$/4/
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s/2$/3/
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s/1$/2/
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s/0$/1/
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# Carry 10s by converting the overflow character `A' to a `0' and
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# incrementing the 10s position.
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s/9A$/A0/
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s/8A$/90/
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s/7A$/80/
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s/6A$/70/
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s/5A$/60/
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s/4A$/50/
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s/3A$/40/
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s/2A$/30/
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s/1A$/20/
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s/0A$/10/
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# Same as above, but for 100s.
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s/^9A/A0/
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s/^8A/90/
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s/^7A/80/
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s/^6A/70/
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s/^5A/60/
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s/^4A/50/
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s/^3A/40/
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s/^2A/30/
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s/^1A/20/
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s/^0A/10/
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# Any remaining carry flags means we can't count any higher.
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/A/!b; q2
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