SPARK Ada使用GNATProve假设GCC内在函数的后置条件
我想在SPARK_模式下创建一个函数,它利用GNAT GCC的内在函数“_builtin_ctzll”SPARK Ada使用GNATProve假设GCC内在函数的后置条件,ada,spark-ada,Ada,Spark Ada,我想在SPARK_模式下创建一个函数,它利用GNAT GCC的内在函数“_builtin_ctzll” 我想假设后置条件为真,因为它是文档中暗示的尾随零数的定义。然而,我不确定如何做到这一点,因为我已经阅读了大量文档,并尝试使用“pragma-aspect”。我对Ada/SPARK比较陌生,正在使用GNAT Community 2020。有人能帮我解决这个问题,让gnatprove能够证明CTZLL的后条件吗?当我使用Shift\u Right制定内置CTZLL的后条件(合同)时,我能够证明(使
我想假设后置条件为真,因为它是文档中暗示的尾随零数的定义。然而,我不确定如何做到这一点,因为我已经阅读了大量文档,并尝试使用“pragma-aspect”。我对Ada/SPARK比较陌生,正在使用GNAT Community 2020。有人能帮我解决这个问题,让gnatprove能够证明CTZLL的后条件吗?当我使用
Shift\u Right
制定内置CTZLL的后条件(合同)时,我能够证明(使用GNAT CE 2020和证明级别1)如果要运行的话,test.adb
没有运行时错误
注:相关文件:SPARK用户手册,第7.4.5节:
内在广告
pragma Assertion_Policy (Check);
with Interfaces; use Interfaces;
package Intrinsic with SPARK_Mode is
-- Count Trailing Zeros (long long unsigned).
function CTZLL (X : Unsigned_64) return Natural with
Pre => X /= 0,
Post => CTZLL'Result in 0 .. Unsigned_64'Size - 1 and
(for all I in 0 .. CTZLL'Result - 1 =>
(Shift_Right (X, I) and 2#1#) = 2#0#) and
(Shift_Right (X, CTZLL'Result) and 2#1#) = 2#1#;
-- You could also use aspects (Import, Convention, External_Name).
pragma Import (Intrinsic, CTZLL, "__builtin_ctzll");
end Intrinsic;
test.adb
pragma Assertion_Policy (Check);
with Interfaces; use Interfaces;
with Intrinsic; use Intrinsic;
procedure Test with SPARK_Mode is
begin
-- Absence of Run-Time Errors (AoRTE) for this program can be proven:
-- Assert_Failure will not be raised at runtime.
pragma Assert (CTZLL ( 1) = 0);
pragma Assert (CTZLL ( 2) = 1);
pragma Assert (CTZLL ( 3) = 0);
pragma Assert (CTZLL ( 4) = 2);
pragma Assert (CTZLL ( 5) = 0);
pragma Assert (CTZLL ( 6) = 1);
pragma Assert (CTZLL ( 7) = 0);
pragma Assert (CTZLL ( 8) = 3);
pragma Assert (CTZLL ( 9) = 0);
pragma Assert (CTZLL (10) = 1);
pragma Assert (CTZLL (2 ** 63 ) = 63);
pragma Assert (CTZLL (2 ** 64 - 1) = 0);
end Test;
with Ada.Text_IO; use Ada.Text_IO;
with Ada.Integer_Text_IO; use Ada.Integer_Text_IO;
with Interfaces; use Interfaces;
with Intrinsic; use Intrinsic;
procedure Main is
begin
for K in 1 .. 10 loop
Put (K, Width => 3);
Put (K, Width => 9, Base => 2);
Put (CTZLL (Unsigned_64 (K)), Width => 4);
New_Line;
end loop;
end Main;
输出(gnatprove的)
对于那些不熟悉\uuuuu builtin\u ctzll
:返回x中尾随0位的数量,从最低有效位位置开始。如果x为0,则结果未定义。另见。例如:
main.adb
pragma Assertion_Policy (Check);
with Interfaces; use Interfaces;
with Intrinsic; use Intrinsic;
procedure Test with SPARK_Mode is
begin
-- Absence of Run-Time Errors (AoRTE) for this program can be proven:
-- Assert_Failure will not be raised at runtime.
pragma Assert (CTZLL ( 1) = 0);
pragma Assert (CTZLL ( 2) = 1);
pragma Assert (CTZLL ( 3) = 0);
pragma Assert (CTZLL ( 4) = 2);
pragma Assert (CTZLL ( 5) = 0);
pragma Assert (CTZLL ( 6) = 1);
pragma Assert (CTZLL ( 7) = 0);
pragma Assert (CTZLL ( 8) = 3);
pragma Assert (CTZLL ( 9) = 0);
pragma Assert (CTZLL (10) = 1);
pragma Assert (CTZLL (2 ** 63 ) = 63);
pragma Assert (CTZLL (2 ** 64 - 1) = 0);
end Test;
with Ada.Text_IO; use Ada.Text_IO;
with Ada.Integer_Text_IO; use Ada.Integer_Text_IO;
with Interfaces; use Interfaces;
with Intrinsic; use Intrinsic;
procedure Main is
begin
for K in 1 .. 10 loop
Put (K, Width => 3);
Put (K, Width => 9, Base => 2);
Put (CTZLL (Unsigned_64 (K)), Width => 4);
New_Line;
end loop;
end Main;
输出(属于Main
)
您无法证明后置条件(gnatprove
需要查看内在代码)。你能做的就是写一个后置条件,让你能够证明使用CTZLL
的代码是正确的;并使用其他方式向您证明,CTZLL
的行为确实符合合同规定。您对后条件的最新更改采纳了我的评论,但该评论似乎尚未发布。这是思想转移吗?!(我可能刚刚忘记发布了!)有没有什么方法可以假设postcondition为真,以证明另一个使用CTZLL的函数?我不知道该怎么做。例如,二进制GCD算法使用CTZLL来大大提高性能。@alfxs如@Simon Wright在其对原始问题的评论中所述,gnatprove
无法证明导入子程序的后置条件成立,因此假设如果先决条件成立,后置条件将成立(在这种情况下,X
和CTZLL
的结果之间的函数关系将保持iffX/=0
)。合同是否(在这种情况下为关系)是否足够准确,或者是否以一种有用的方式来证明算法中的其他条件(其中CTZLL
是算法的一部分),取决于要在算法中验证的条件。@alfxs既然您提到了GCD算法:有一篇很好的博客文章讨论了证明函数的方法使用SPARK的GCD算法的nal行为:。您可能已经找到了它,但我想我提到它是为了完整性。代码在GNAT CE 2020中提供(GNAT Studio>帮助>SPARK>示例>GCD)。
$ ./obj/main
1 2#1# 0
2 2#10# 1
3 2#11# 0
4 2#100# 2
5 2#101# 0
6 2#110# 1
7 2#111# 0
8 2#1000# 3
9 2#1001# 0
10 2#1010# 1