From 15c338a9d07d262c52887ad644392c61d7952ef0 Mon Sep 17 00:00:00 2001
From: Richard Hull <rm_hull@yahoo.co.uk>
Date: Tue, 31 May 2016 21:39:01 +0100
Subject: [PATCH] Initial port from .cljs -> .clj

---
 src/boyer_moore/core.clj       | 119 +++++++++++++++++++++++++++++++++
 test/boyer_moore/core_test.clj |  29 ++++++++
 2 files changed, 148 insertions(+)
 create mode 100644 src/boyer_moore/core.clj
 create mode 100644 test/boyer_moore/core_test.clj

diff --git a/src/boyer_moore/core.clj b/src/boyer_moore/core.clj
new file mode 100644
index 0000000..ebdf69e
--- /dev/null
+++ b/src/boyer_moore/core.clj
@@ -0,0 +1,119 @@
+(ns boyer-moore.core)
+
+; ported directly from the Java version at wikipedia:
+; http://en.wikipedia.org/wiki/Boyer_moore#Implementations
+
+(defn- char-code-at [s i]
+  (int (get s i)))
+
+(defn- char=
+  ([s i j]
+    (char= s s i j))
+
+  ([s1 s2 i j]
+    (= (get s1 i) (get s2 j))))
+
+(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
+
+        (not (char= needle (inc i) (inc j)))
+        false
+
+        :else
+        (recur (inc i) (inc j))))))
+
+(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)))
+
+(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)))))))
+
+(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))))))))
+
+(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))))))))
+
+(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))
+
+  ([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
+
+              (neg? j)
+              (inc i)
+
+              (char= haystack needle i j)
+              (recur (dec i) (dec j))
+
+              :else
+              (recur (calc-offset i j) m1))))))))
\ No newline at end of file
diff --git a/test/boyer_moore/core_test.clj b/test/boyer_moore/core_test.clj
new file mode 100644
index 0000000..b884925
--- /dev/null
+++ b/test/boyer_moore/core_test.clj
@@ -0,0 +1,29 @@
+(ns boyer-moore.core-test
+  (:require
+    [clojure.test :refer :all]
+    [boyer-moore.core :refer [index-of]]))
+
+(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)))
+
+;(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")))
\ No newline at end of file