Boyer-Moore algorithm

Second of three pattern search algorithms.

Author: mkitzan

Pattern_Search/DFA_Test.adb

@@ -1,18 +1,25 @@
-with Ada.Text_IO, Pattern_Search; use Ada.Text_IO, Pattern_Search;
+with Ada.Text_IO; use Ada.Text_IO;
+with Pattern_Search_KMP, Pattern_Search_BM;
+
 
 procedure DFA_Test is
     Text : String := "this is a test string";
     Pattern : String := "test";
     N : Positive;
 begin
-    N := Search(Text => Text, Pattern => Pattern);
-
     Put_Line(Text);
-    
+
+    N := Pattern_Search_KMP.Search(Text => Text, Pattern => Pattern);
     for I in 1 .. N
     loop
         Put(' ');
     end loop;
+    Put_Line(Pattern);
 
+    N := Pattern_Search_BM.Search(Text => Text, Pattern => Pattern);
+    for I in 1 .. N
+    loop
+        Put(' ');
+    end loop;
     Put_Line(Pattern);
 end DFA_Test;

Pattern_Search/Pattern_Search_BM.adb

@@ -0,0 +1,51 @@
+
+package body Pattern_Search_BM is
+    function Search (Text, Pattern : in String) return Positive is
+        Right_Array : Right(' ' .. '~');
+        N : Positive := Text'Length;
+        M : Positive := Pattern'Length;
+        I : Positive := 1;
+        Skip : Integer;
+    begin
+        Build_Right(Right_Array, Pattern);
+        
+        while I <= N-M
+        loop
+            Skip := 0;
+            
+            for J in reverse 1 .. M
+            loop
+                if Pattern(J) /= Text(I+J-1) then
+                    if J-Right_Array(Text(I+J-1)) < 1 then 
+                        Skip := 1;
+                    else 
+                        Skip := J-Right_Array(Text(I+J-1));
+                    end if;
+                    
+                    exit;
+                end if;
+            end loop;
+            
+            if Skip = 0 then
+                return I - 1;
+            end if;
+            
+            I := I + Skip;
+        end loop;
+        
+        return N;
+    end Search;
+
+    procedure Build_Right (Right_Array : in out Right; Pattern : in String) is
+    begin
+        for C in Right_Array'range
+        loop
+            Right_Array(C) := 0;
+        end loop;
+        
+        for I in Pattern'range
+        loop
+            Right_Array(Pattern(I)) := I;
+        end loop;
+    end Build_Right;
+end Pattern_Search_BM;

Pattern_Search/Pattern_Search_BM.ads

@@ -0,0 +1,9 @@
+
+package Pattern_Search_BM is
+    -- accepts all printable ascii characters
+    type Right is array (Character range <>) of Integer;
+    
+    function Search (Text, Pattern : in String) return Positive;
+private
+    procedure Build_Right(Right_Array : in out Right; Pattern : in String);
+end Pattern_Search_BM;

Pattern_Search/Pattern_Search_KMP.adb

@@ -1,4 +1,3 @@
-with Ada.Text_IO; use Ada.Text_IO;
 
 package body Pattern_Search_KMP is
     function Search (Text, Pattern : in String) return Positive is