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1 ------------------------------------------------------------------------------
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2 -- --
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3 -- GNAT RUN-TIME COMPONENTS --
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4 -- --
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5 -- S Y S T E M . A T O M I C _ C O U N T E R S --
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6 -- --
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7 -- B o d y --
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8 -- --
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131
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9 -- Copyright (C) 2011-2018, 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 implements Atomic_Counter and Atomic_Unsigned operations
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33 -- for platforms where GCC supports __sync_add_and_fetch_4 and
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34 -- __sync_sub_and_fetch_4 builtins.
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35
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36 package body System.Atomic_Counters is
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37
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38 procedure Sync_Add_And_Fetch
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39 (Ptr : access Atomic_Unsigned;
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40 Value : Atomic_Unsigned);
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41 pragma Import (Intrinsic, Sync_Add_And_Fetch, "__sync_add_and_fetch_4");
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42
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43 function Sync_Sub_And_Fetch
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44 (Ptr : access Atomic_Unsigned;
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45 Value : Atomic_Unsigned) return Atomic_Unsigned;
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46 pragma Import (Intrinsic, Sync_Sub_And_Fetch, "__sync_sub_and_fetch_4");
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47
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48 ---------------
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49 -- Decrement --
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50 ---------------
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51
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52 procedure Decrement (Item : aliased in out Atomic_Unsigned) is
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53 begin
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54 if Sync_Sub_And_Fetch (Item'Unrestricted_Access, 1) = 0 then
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55 null;
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56 end if;
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57 end Decrement;
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58
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59 function Decrement (Item : aliased in out Atomic_Unsigned) return Boolean is
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60 begin
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61 return Sync_Sub_And_Fetch (Item'Unrestricted_Access, 1) = 0;
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62 end Decrement;
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63
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64 function Decrement (Item : in out Atomic_Counter) return Boolean is
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65 begin
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66 -- Note: the use of Unrestricted_Access here is required because we
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67 -- are obtaining an access-to-volatile pointer to a non-volatile object.
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68 -- This is not allowed for [Unchecked_]Access, but is safe in this case
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69 -- because we know that no aliases are being created.
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70
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71 return Sync_Sub_And_Fetch (Item.Value'Unrestricted_Access, 1) = 0;
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72 end Decrement;
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73
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74 ---------------
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75 -- Increment --
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76 ---------------
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77
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78 procedure Increment (Item : aliased in out Atomic_Unsigned) is
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79 begin
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80 Sync_Add_And_Fetch (Item'Unrestricted_Access, 1);
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81 end Increment;
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82
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83 procedure Increment (Item : in out Atomic_Counter) is
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84 begin
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85 -- Note: the use of Unrestricted_Access here is required because we are
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86 -- obtaining an access-to-volatile pointer to a non-volatile object.
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87 -- This is not allowed for [Unchecked_]Access, but is safe in this case
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88 -- because we know that no aliases are being created.
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89
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90 Sync_Add_And_Fetch (Item.Value'Unrestricted_Access, 1);
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91 end Increment;
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92
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93 ----------------
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94 -- Initialize --
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95 ----------------
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96
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97 procedure Initialize (Item : out Atomic_Counter) is
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98 begin
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99 Item.Value := 1;
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100 end Initialize;
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101
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102 ------------
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103 -- Is_One --
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104 ------------
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105
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106 function Is_One (Item : Atomic_Counter) return Boolean is
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107 begin
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108 return Item.Value = 1;
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109 end Is_One;
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110
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111 end System.Atomic_Counters;
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