checksums.fletcher: adding Fletcher's checksum in 16/32/64-bits.

basis/checksums/fletcher/authors.txt

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+John Benediktsson

basis/checksums/fletcher/fletcher-docs.factor

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+USING: help.markup help.syntax ;
+IN: checksums.fletcher
+
+HELP: fletcher-16
+{ $class-description "Fletcher's 16-bit checksum algorithm." } ;
+
+HELP: fletcher-32
+{ $class-description "Fletcher's 32-bit checksum algorithm." } ;
+
+HELP: fletcher-64
+{ $class-description "Fletcher's 64-bit checksum algorithm." } ;
+
+ARTICLE: "checksums.fletcher" "Fletcher's checksum"
+"The Fletcher checksum is an algorithm for computing a position-dependent checksum devised by John G. Fletcher at Lawrence Livermore Labs in the late 1970s."
+{ $subsections fletcher-16 fletcher-32 fletcher-64 } ;
+
+ABOUT: "checksums.fletcher"

basis/checksums/fletcher/fletcher-tests.factor

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+USING: checksums kernel sequences tools.test ;
+IN: checksums.fletcher
+
+{
+    { 51440 3948201259 14034561336514601929 }
+} [
+    "abcde" { fletcher-16 fletcher-32 fletcher-64 }
+    [ checksum-bytes ] with map
+] unit-test
+

basis/checksums/fletcher/fletcher.factor

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+! Copyright (C) 2013 John Benediktsson
+! See http://factorcode.org/license.txt for BSD license
+
+USING: checksums grouping io.binary kernel locals math sequences
+;
+
+IN: checksums.fletcher
+
+SINGLETON: fletcher-16
+SINGLETON: fletcher-32
+SINGLETON: fletcher-64
+
+INSTANCE: fletcher-16 checksum
+INSTANCE: fletcher-32 checksum
+INSTANCE: fletcher-64 checksum
+
+:: fletcher ( seq k -- n )
+    k 16 / :> chars
+    k 2 / 2^ :> base
+    base 1 - :> modulo
+    0 0 seq chars <groups> [
+        be> + modulo mod [ + modulo mod ] keep
+    ] each [ base * ] [ + ] bi* ; inline
+
+M: fletcher-16 checksum-bytes drop 16 fletcher ;
+M: fletcher-32 checksum-bytes drop 32 fletcher ;
+M: fletcher-64 checksum-bytes drop 64 fletcher ;

basis/checksums/fletcher/summary.txt

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+Fletcher's checksum algorithm