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(ns boyer-moore.core) | ||
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; ported directly from the Java version at wikipedia: | ||
; http://en.wikipedia.org/wiki/Boyer_moore#Implementations | ||
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(defn- char-code-at [s i] | ||
(int (get s i))) | ||
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(defn- char= | ||
([s i j] | ||
(char= s s i j)) | ||
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([s1 s2 i j] | ||
(= (get s1 i) (get s2 j)))) | ||
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(defn- prefix? | ||
"Is needle[p:end] a prefix of needle?" | ||
[needle p] | ||
(let [len (count needle)] | ||
(loop [i p | ||
j 0] | ||
(cond | ||
(= i len) | ||
true | ||
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(not (char= needle (inc i) (inc j))) | ||
false | ||
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:else | ||
(recur (inc i) (inc j)))))) | ||
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(defn- suffix-length | ||
"Returns the maximum length of the substring ends at p and is a suffix" | ||
[needle p] | ||
(loop [i p | ||
j (dec (count needle)) | ||
len 0] | ||
(if (and (> i 0) (char= needle i j)) | ||
(recur (dec i) (dec j) (inc len)) | ||
len))) | ||
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(defn- make-char-table | ||
"Makes the jump table based on the mismatched character information" | ||
[needle] | ||
(let [len (count needle)] | ||
(loop [i 0 | ||
table (transient (vec (repeat 256 len)))] | ||
(if-not (< i (dec len)) | ||
(persistent! table) | ||
(recur | ||
(inc i) | ||
(assoc! | ||
table | ||
(char-code-at needle i) | ||
(- len 1 i))))))) | ||
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(defn- calc-prefixes [needle] | ||
(let [len (count needle)] | ||
(loop [i (dec len) | ||
last-posn len | ||
table (transient (vec (repeat len 0)))] | ||
(if-not (>= i 0) | ||
(persistent! table) | ||
(let [last-posn (if (prefix? needle i) i last-posn)] | ||
(recur | ||
(dec i) | ||
last-posn | ||
(assoc! | ||
table | ||
(- len 1 i) | ||
(+ last-posn (- i) len -1)))))))) | ||
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(defn- make-offset-table | ||
"Makes the jump table based on the scan offset which mismatch occurs" | ||
[needle] | ||
(let [len (count needle)] | ||
(loop [i 0 | ||
table (transient (calc-prefixes needle))] | ||
(if-not (< i (dec len)) | ||
(persistent! table) | ||
(let [slen (suffix-length needle i)] | ||
(recur | ||
(inc i) | ||
(assoc! table slen (+ len -1 (- i) slen)))))))) | ||
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(defn index-of | ||
"Returns the index with the string of the first occurrence of the | ||
specified substring. If it is not a substring, return nil. | ||
haystack - the string to be scanned | ||
needle - the target string to search" | ||
([haystack needle] | ||
(index-of haystack needle 0)) | ||
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([haystack needle offset] | ||
(let [len (count needle) | ||
m1 (dec len)] | ||
(if (zero? len) | ||
offset | ||
(let [char-table (make-char-table needle) | ||
offset-table (make-offset-table needle) | ||
calc-offset (fn [i j] (+ i | ||
(Math/max | ||
(char-code-at offset-table (- m1 j)) | ||
(char-code-at char-table (char-code-at haystack i)))))] | ||
(loop [i (+ offset m1) | ||
j m1] | ||
(cond | ||
(>= i (count haystack)) | ||
nil | ||
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(neg? j) | ||
(inc i) | ||
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(char= haystack needle i j) | ||
(recur (dec i) (dec j)) | ||
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:else | ||
(recur (calc-offset i j) m1)))))))) |
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(ns boyer-moore.core-test | ||
(:require | ||
[clojure.test :refer :all] | ||
[boyer-moore.core :refer [index-of]])) | ||
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(deftest boyer-moore->string | ||
(is (= (index-of "Hello world" "") 0)) | ||
(is (= (index-of "Hello world" "" 3) 3)) | ||
(is (= (index-of "Hello world" "Hello") 0)) | ||
(is (= (index-of "Hello world" "world") 6)) | ||
(is (= (index-of "Hello world" "world" 4) 6)) | ||
(is (= (index-of "Hello world" "o wo") 4)) | ||
(is (= (index-of "Hello world" "not") nil)) | ||
(is (= (index-of "svertices vertices" "vertices") 1)) | ||
(is (= (index-of "FFS :svertices :vertices" ":vertices") 15))) | ||
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;(deftest boyer-moore->dataview | ||
; (let [data (str | ||
; "Rent a flat above a shop!\n" | ||
; "Cut your hair and get a job!\n" | ||
; "Smoke some fags and play some pool.") | ||
; dataview (create-dataview (count data))] | ||
; | ||
; (set-binary-data! dataview 0 (seq data)) | ||
; | ||
; (is= (index-of dataview "") 0 "Empty string") | ||
; (is= (index-of dataview "Cut your") 26 "Match at start of 2nd line") | ||
; (is= (index-of dataview "Common People") nil "No match") | ||
; (is= (index-of dataview "above a shop" 26) nil "No match with offset"))) |