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------------------------------------------------------------------------------
-- --
-- GNAT COMPILER COMPONENTS --
-- --
-- S Y S T E M . B I G N U M S --
-- --
-- S p e c --
-- --
-- Copyright (C) 2012, Free Software Foundation, Inc. --
-- --
-- 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/>. --
-- --
-- GNAT was originally developed by the GNAT team at New York University. --
-- Extensive contributions were provided by Ada Core Technologies Inc. --
-- --
------------------------------------------------------------------------------
-- This package provides arbitrary precision signed integer arithmetic for
-- use in computing intermediate values in expressions for the case where
-- pragma Overflow_Check (Eliminated) is in effect.
with Interfaces;
package System.Bignums is
pragma Assert (Long_Long_Integer'Size = 64);
-- This package assumes that Long_Long_Integer size is 64 bit (i.e. that it
-- has a range of -2**63 to 2**63-1). The front end ensures that the mode
-- ELIMINATED is not allowed for overflow checking if this is not the case.
subtype Length is Natural range 0 .. 2 ** 23 - 1;
-- Represent number of words in Digit_Vector
Base : constant := 2 ** 32;
-- Digit vectors use this base
subtype SD is Interfaces.Unsigned_32;
-- Single length digit
type Digit_Vector is array (Length range <>) of SD;
-- Represent digits of a number (most significant digit first)
type Bignum_Data (Len : Length) is record
Neg : Boolean;
-- Set if value is negative, never set for zero
D : Digit_Vector (1 .. Len);
-- Digits of number, most significant first, represented in base
-- 2**Base. No leading zeroes are stored, and the value of zero is
-- represented using an empty vector for D.
end record;
for Bignum_Data use record
Len at 0 range 0 .. 23;
Neg at 3 range 0 .. 7;
end record;
type Bignum is access all Bignum_Data;
-- This is the type that is used externally. Possibly this could be a
-- private type, but we leave the structure exposed for now. For one
-- thing it helps with debugging. Note that this package never shares
-- an allocated Bignum value, so for example for X + 0, a copy of X is
-- returned, not X itself.
-- Note: none of the subprograms in this package modify the Bignum_Data
-- records referenced by Bignum arguments of mode IN.
function Big_Add (X, Y : Bignum) return Bignum; -- "+"
function Big_Sub (X, Y : Bignum) return Bignum; -- "-"
function Big_Mul (X, Y : Bignum) return Bignum; -- "*"
function Big_Div (X, Y : Bignum) return Bignum; -- "/"
function Big_Exp (X, Y : Bignum) return Bignum; -- "**"
function Big_Mod (X, Y : Bignum) return Bignum; -- "mod"
function Big_Rem (X, Y : Bignum) return Bignum; -- "rem"
function Big_Neg (X : Bignum) return Bignum; -- "-"
function Big_Abs (X : Bignum) return Bignum; -- "abs"
-- Perform indicated arithmetic operation on bignum values. No exception
-- raised except for Div/Mod/Rem by 0 which raises Constraint_Error with
-- an appropriate message.
function Big_EQ (X, Y : Bignum) return Boolean; -- "="
function Big_NE (X, Y : Bignum) return Boolean; -- "/="
function Big_GE (X, Y : Bignum) return Boolean; -- ">="
function Big_LE (X, Y : Bignum) return Boolean; -- "<="
function Big_GT (X, Y : Bignum) return Boolean; -- ">"
function Big_LT (X, Y : Bignum) return Boolean; -- "<"
-- Perform indicated comparison on bignums, returning result as Boolean.
-- No exception raised for any input arguments.
function Bignum_In_LLI_Range (X : Bignum) return Boolean;
-- Returns True if the Bignum value is in the range of Long_Long_Integer,
-- so that a call to From_Bignum is guaranteed not to raise an exception.
function To_Bignum (X : Long_Long_Integer) return Bignum;
-- Convert Long_Long_Integer to Bignum. No exception can be raised for any
-- input argument.
function From_Bignum (X : Bignum) return Long_Long_Integer;
-- Convert Bignum to Long_Long_Integer. Constraint_Error raised with
-- appropriate message if value is out of range of Long_Long_Integer.
end System.Bignums;
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