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------------------------------------------------------------------------------
-- --
-- GNAT RUN-TIME COMPONENTS --
-- --
-- GNAT.BINARY_SEARCH --
-- --
-- S p e c --
-- --
-- Copyright (C) 2022-2023, AdaCore --
-- --
-- GNAT is free software; you can redistribute it and/or modify it under --
-- terms of the GNU General Public License as published by the Free Soft- --
-- ware Foundation; either version 3, or (at your option) any later ver- --
-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
-- or FITNESS FOR A PARTICULAR PURPOSE. --
-- --
-- As a special exception under Section 7 of GPL version 3, you are granted --
-- additional permissions described in the GCC Runtime Library Exception, --
-- version 3.1, as published by the Free Software Foundation. --
-- --
-- You should have received a copy of the GNU General Public License and --
-- a copy of the GCC Runtime Library Exception along with this program; --
-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
-- <http://www.gnu.org/licenses/>. --
------------------------------------------------------------------------------
-- Allow binary search of a sorted array (or of an array-like container;
-- the generic does not reference the array directly).
package GNAT.Binary_Search is
generic
type Index_Type is (<>);
type Element_Type (<>) is private;
with function Get (Index : Index_Type) return Element_Type;
with function Before (Left, Right : Element_Type) return Boolean;
Leftmost : Boolean := True;
function Index
(First, Last, Start : Index_Type;
Element : Element_Type) return Index_Type'Base;
-- Search for element in sorted container. Function Before should return
-- True when Left and Right are in the container's sort order and not
-- equal. Function Get returns the container element indexed by Index;
-- Index will be in the range First .. Last. If there is at least one index
-- value in the range First .. Last for which Get would return Element,
-- then the Leftmost generic parameter indicates whether the least (if
-- Leftmost is True) or the greatest (if Leftmost is False) such index
-- value is returned. If no such index value exists, then Leftmost
-- determines whether to return the greater (if Leftmost is True) or the
-- smaller (if Leftmost is False) of the two index values between which
-- Element could be inserted. If First > Last (so that a null range is
-- being searched), some Index_Type'Base value will be returned.
-- Start is the index for the first probe of the binary search. It can
-- improve speed of many search operations when user can guess the most
-- likely values. If you do not know what value should be used there, use
-- (First + Last) / 2.
generic
type Index_Type is (<>);
type Element_Type (<>) is private;
with function Before
(Index : Index_Type; Element : Element_Type) return Boolean;
function Leftmost
(First, Last, Start : Index_Type;
Element : Element_Type) return Index_Type'Base
with Pre => First > Last -- Empty array
or else (Start in First .. Last
and then ( -- To prevent overflow in function result
Index_Type'Base'Last > Last
or else not Before (Last, Element)));
-- Leftmost returns the result described for Index in the case where the
-- Leftmost parameter is True, with Index_Type values mapped to
-- Element_Type values via Get as needed.
generic
type Index_Type is (<>);
type Element_Type (<>) is private;
with function Before
(Element : Element_Type; Index : Index_Type) return Boolean;
function Rightmost
(First, Last, Start : Index_Type;
Element : Element_Type) return Index_Type'Base
with Pre => First > Last -- Empty array
or else (Start in First .. Last
and then ( -- To prevent overflow in function result
Index_Type'Base'First < First
or else not Before (Element, First)));
-- Rightmost returns the result described for Index in the case where the
-- Leftmost parameter is False, with Index_Type values mapped to
-- Element_Type values via Get as needed.
end GNAT.Binary_Search;
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