gcc/ada/libgnat/s-bignum.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT COMPILER COMPONENTS                         --
   4 --                                                                          --
   5 --                       S Y S T E M . B I G N U M S                        --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --            Copyright (C) 2012-2018, Free Software Foundation, Inc.       --
  10 --                                                                          --
  11 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 3,  or (at your option) any later ver- --
  14 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
  17 --                                                                          --
  18 -- As a special exception under Section 7 of GPL version 3, you are granted --
  19 -- additional permissions described in the GCC Runtime Library Exception,   --
  20 -- version 3.1, as published by the Free Software Foundation.               --
  21 --                                                                          --
  22 -- You should have received a copy of the GNU General Public License and    --
  23 -- a copy of the GCC Runtime Library Exception along with this program;     --
  24 -- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
  25 -- <http://www.gnu.org/licenses/>.                                          --
  26 --                                                                          --
  27 -- GNAT was originally developed  by the GNAT team at  New York University. --
  28 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  29 --                                                                          --
  30 ------------------------------------------------------------------------------
  31
  32 --  This package provides arbitrary precision signed integer arithmetic for
  33 --  use in computing intermediate values in expressions for the case where
  34 --  pragma Overflow_Check (Eliminated) is in effect.
  35
  36 with Interfaces;
  37
  38 package System.Bignums is
  39
  40    pragma Assert (Long_Long_Integer'Size = 64);
  41    --  This package assumes that Long_Long_Integer size is 64 bit (i.e. that it
  42    --  has a range of -2**63 to 2**63-1). The front end ensures that the mode
  43    --  ELIMINATED is not allowed for overflow checking if this is not the case.
  44
  45    subtype Length is Natural range 0 .. 2 ** 23 - 1;
  46    --  Represent number of words in Digit_Vector
  47
  48    Base : constant := 2 ** 32;
  49    --  Digit vectors use this base
  50
  51    subtype SD is Interfaces.Unsigned_32;
  52    --  Single length digit
  53
  54    type Digit_Vector is array (Length range <>) of SD;
  55    --  Represent digits of a number (most significant digit first)
  56
  57    type Bignum_Data (Len : Length) is record
  58       Neg : Boolean;
  59       --  Set if value is negative, never set for zero
  60
  61       D : Digit_Vector (1 .. Len);
  62       --  Digits of number, most significant first, represented in base
  63       --  2**Base. No leading zeroes are stored, and the value of zero is
  64       --  represented using an empty vector for D.
  65    end record;
  66
  67    for Bignum_Data use record
  68       Len at 0 range 0 .. 23;
  69       Neg at 3 range 0 .. 7;
  70    end record;
  71
  72    type Bignum is access all Bignum_Data;
  73    --  This is the type that is used externally. Possibly this could be a
  74    --  private type, but we leave the structure exposed for now. For one
  75    --  thing it helps with debugging. Note that this package never shares
  76    --  an allocated Bignum value, so for example for X + 0, a copy of X is
  77    --  returned, not X itself.
  78
  79    --  Note: none of the subprograms in this package modify the Bignum_Data
  80    --  records referenced by Bignum arguments of mode IN.
  81
  82    function Big_Add (X, Y : Bignum) return Bignum;  --  "+"
  83    function Big_Sub (X, Y : Bignum) return Bignum;  --  "-"
  84    function Big_Mul (X, Y : Bignum) return Bignum;  --  "*"
  85    function Big_Div (X, Y : Bignum) return Bignum;  --  "/"
  86    function Big_Exp (X, Y : Bignum) return Bignum;  --  "**"
  87    function Big_Mod (X, Y : Bignum) return Bignum;  --  "mod"
  88    function Big_Rem (X, Y : Bignum) return Bignum;  --  "rem"
  89    function Big_Neg (X    : Bignum) return Bignum;  --  "-"
  90    function Big_Abs (X    : Bignum) return Bignum;  --  "abs"
  91    --  Perform indicated arithmetic operation on bignum values. No exception
  92    --  raised except for Div/Mod/Rem by 0 which raises Constraint_Error with
  93    --  an appropriate message.
  94
  95    function Big_EQ  (X, Y : Bignum) return Boolean;  -- "="
  96    function Big_NE  (X, Y : Bignum) return Boolean;  -- "/="
  97    function Big_GE  (X, Y : Bignum) return Boolean;  -- ">="
  98    function Big_LE  (X, Y : Bignum) return Boolean;  -- "<="
  99    function Big_GT  (X, Y : Bignum) return Boolean;  --  ">"
 100    function Big_LT  (X, Y : Bignum) return Boolean;  --  "<"
 101    --  Perform indicated comparison on bignums, returning result as Boolean.
 102    --  No exception raised for any input arguments.
 103
 104    function Bignum_In_LLI_Range (X : Bignum) return Boolean;
 105    --  Returns True if the Bignum value is in the range of Long_Long_Integer,
 106    --  so that a call to From_Bignum is guaranteed not to raise an exception.
 107
 108    function To_Bignum (X : Long_Long_Integer) return Bignum;
 109    --  Convert Long_Long_Integer to Bignum. No exception can be raised for any
 110    --  input argument.
 111
 112    function From_Bignum (X : Bignum) return Long_Long_Integer;
 113    --  Convert Bignum to Long_Long_Integer. Constraint_Error raised with
 114    --  appropriate message if value is out of range of Long_Long_Integer.
 115
 116 end System.Bignums;