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1 ------------------------------------------------------------------------------
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2 -- --
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3 -- GNAT COMPILER COMPONENTS --
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4 -- --
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5 -- S Y S T E M . B I G N U M S --
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6 -- --
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7 -- S p e c --
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8 -- --
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131
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9 -- Copyright (C) 2012-2018, Free Software Foundation, Inc. --
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111
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10 -- --
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11 -- GNAT is free software; you can redistribute it and/or modify it under --
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12 -- terms of the GNU General Public License as published by the Free Soft- --
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13 -- ware Foundation; either version 3, or (at your option) any later ver- --
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14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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16 -- or FITNESS FOR A PARTICULAR PURPOSE. --
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17 -- --
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18 -- As a special exception under Section 7 of GPL version 3, you are granted --
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19 -- additional permissions described in the GCC Runtime Library Exception, --
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20 -- version 3.1, as published by the Free Software Foundation. --
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21 -- --
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22 -- You should have received a copy of the GNU General Public License and --
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23 -- a copy of the GCC Runtime Library Exception along with this program; --
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24 -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
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25 -- <http://www.gnu.org/licenses/>. --
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26 -- --
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27 -- GNAT was originally developed by the GNAT team at New York University. --
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28 -- Extensive contributions were provided by Ada Core Technologies Inc. --
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29 -- --
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30 ------------------------------------------------------------------------------
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31
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32 -- This package provides arbitrary precision signed integer arithmetic for
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33 -- use in computing intermediate values in expressions for the case where
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34 -- pragma Overflow_Check (Eliminated) is in effect.
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35
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36 with Interfaces;
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37
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38 package System.Bignums is
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39
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40 pragma Assert (Long_Long_Integer'Size = 64);
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41 -- This package assumes that Long_Long_Integer size is 64 bit (i.e. that it
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42 -- has a range of -2**63 to 2**63-1). The front end ensures that the mode
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43 -- ELIMINATED is not allowed for overflow checking if this is not the case.
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44
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45 subtype Length is Natural range 0 .. 2 ** 23 - 1;
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46 -- Represent number of words in Digit_Vector
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47
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48 Base : constant := 2 ** 32;
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49 -- Digit vectors use this base
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50
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51 subtype SD is Interfaces.Unsigned_32;
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52 -- Single length digit
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53
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54 type Digit_Vector is array (Length range <>) of SD;
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55 -- Represent digits of a number (most significant digit first)
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56
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57 type Bignum_Data (Len : Length) is record
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58 Neg : Boolean;
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59 -- Set if value is negative, never set for zero
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60
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61 D : Digit_Vector (1 .. Len);
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62 -- Digits of number, most significant first, represented in base
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63 -- 2**Base. No leading zeroes are stored, and the value of zero is
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64 -- represented using an empty vector for D.
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65 end record;
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66
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67 for Bignum_Data use record
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68 Len at 0 range 0 .. 23;
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69 Neg at 3 range 0 .. 7;
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70 end record;
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71
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72 type Bignum is access all Bignum_Data;
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73 -- This is the type that is used externally. Possibly this could be a
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74 -- private type, but we leave the structure exposed for now. For one
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75 -- thing it helps with debugging. Note that this package never shares
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76 -- an allocated Bignum value, so for example for X + 0, a copy of X is
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77 -- returned, not X itself.
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78
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79 -- Note: none of the subprograms in this package modify the Bignum_Data
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80 -- records referenced by Bignum arguments of mode IN.
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81
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82 function Big_Add (X, Y : Bignum) return Bignum; -- "+"
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83 function Big_Sub (X, Y : Bignum) return Bignum; -- "-"
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84 function Big_Mul (X, Y : Bignum) return Bignum; -- "*"
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85 function Big_Div (X, Y : Bignum) return Bignum; -- "/"
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86 function Big_Exp (X, Y : Bignum) return Bignum; -- "**"
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87 function Big_Mod (X, Y : Bignum) return Bignum; -- "mod"
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88 function Big_Rem (X, Y : Bignum) return Bignum; -- "rem"
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89 function Big_Neg (X : Bignum) return Bignum; -- "-"
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90 function Big_Abs (X : Bignum) return Bignum; -- "abs"
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91 -- Perform indicated arithmetic operation on bignum values. No exception
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92 -- raised except for Div/Mod/Rem by 0 which raises Constraint_Error with
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93 -- an appropriate message.
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94
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95 function Big_EQ (X, Y : Bignum) return Boolean; -- "="
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96 function Big_NE (X, Y : Bignum) return Boolean; -- "/="
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97 function Big_GE (X, Y : Bignum) return Boolean; -- ">="
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98 function Big_LE (X, Y : Bignum) return Boolean; -- "<="
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99 function Big_GT (X, Y : Bignum) return Boolean; -- ">"
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100 function Big_LT (X, Y : Bignum) return Boolean; -- "<"
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101 -- Perform indicated comparison on bignums, returning result as Boolean.
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102 -- No exception raised for any input arguments.
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103
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104 function Bignum_In_LLI_Range (X : Bignum) return Boolean;
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105 -- Returns True if the Bignum value is in the range of Long_Long_Integer,
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106 -- so that a call to From_Bignum is guaranteed not to raise an exception.
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107
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108 function To_Bignum (X : Long_Long_Integer) return Bignum;
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109 -- Convert Long_Long_Integer to Bignum. No exception can be raised for any
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110 -- input argument.
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111
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112 function From_Bignum (X : Bignum) return Long_Long_Integer;
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113 -- Convert Bignum to Long_Long_Integer. Constraint_Error raised with
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114 -- appropriate message if value is out of range of Long_Long_Integer.
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115
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116 end System.Bignums;
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