c – GMP pow中的溢出处理

(我只是GMP-library的间接用户,主要是通过 swi-prolog和 yap.但我对解决这个问题非常感兴趣.)

当使用可笑的大值执行取幂时,主机系统或GMP不再能够适当地处理溢出.我已经与上述系统的开发人员进行了交谈,但他们没有看到一个简单的解决方案.

这个问题是否为其他GMP系统/用户所知？你如何处理这种溢出？

作为一个完整性检查首先测试7 ^ 7 ^ 7的值应该是：375982 … 32343

在32位系统上,例如查询？ – X是13 ^ 1150000000.产生这样的溢出.以下是YAP给出的内容：

GNU gdb (GDB) 7.0-ubuntu
copyright (C) 2009 Free Software Foundation,Inc.
License GPLv3+: GNU GPL version 3 or later 
This is free software: you are free to change and redistribute it.
There is NO WARRANTY,to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "i486-linux-gnu".
For bug reporting instructions,please see:
...
Reading symbols from /opt/gupu/src/yap-6.3/narch-gupu2/yap...done.
(gdb) run -f
Starting program: /opt/gupu/src/yap-6.3/narch-gupu2/yap -f
YAP 6.3.2 (i686-linux): Sun Nov 11 04:19:37 CET 2012
?- X is 13^1150000000.

Program received signal SIGSEGV,Segmentation fault.
0x001638d8 in ?? () from /usr/lib/libgmp.so.3
(gdb) bt
#0  0x001638d8 in ?? () from /usr/lib/libgmp.so.3
#1  0x00164470 in __gmpn_mul_fft () from /usr/lib/libgmp.so.3
#2  0x001646c2 in __gmpn_mul_fft_full () from /usr/lib/libgmp.so.3
#3  0x00165f28 in __gmpn_sqr_n () from /usr/lib/libgmp.so.3
#4  0x0014b58b in __gmpz_n_pow_ui () from /usr/lib/libgmp.so.3
#5  0x0014c4a1 in __gmpz_pow_ui () from /usr/lib/libgmp.so.3
#6  0x080c4a1d in Yap_gmp_exp_int_int (i1=13,i2=1150000000) at ../C/gmp_support.c:939
#7  0x0815f9df in p_exp (t1=,t2=3082051592) at ../C/arith2.c:609
#8  0x080b1f19 in Eval (t=0) at ../C/eval.c:147
#9  0x080b2251 in p_is () at ../C/eval.c:186
#10 0x0806b56a in Yap_absmi (inp=0) at ../C/absmi.c:6912
#11 0x080b3655 in exec_absmi (top=) at ../C/exec.c:1002
#12 0x080b3b1f in do_goal (t=,CodeAdr=,arity=,pt=0x0,top=1) at ../C/exec.c:1068
#13 0x080b3d1d in Yap_RunTopGoal (t=135918154) at ../C/exec.c:1291
#14 0x08061a6f in YAP_RunGoalOnce (t=135918154) at ../C/c_interface.c:2511
#15 0x0805c2f5 in do_top_goal (argc=2,argv=0xbffff4c4) at ../console/yap.c:84
#16 exec_top_level (argc=2,argv=0xbffff4c4) at ../console/yap.c:131
#17 main (argc=2,argv=0xbffff4c4) at ../console/yap.c:172
(gdb)

编辑：对于64位系统也是如此;像这样：

Welcome to SWI-Prolog (Multi-threaded,64 bits,Version 6.3.5)
copyright (c) 1990-2012 University of Amsterdam,VU Amsterdam
SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software,and you are welcome to redistribute it under certain conditions.
Please visit http://www.swi-prolog.org for details.

For help,use ?- help(Topic). or ?- apropos(Word).

?- X is 3445^2^62.
gmp: overflow in mpz type
Abort

然而,

?- X is 2^2^63.
ERROR: Out of global stack
?- X is 2^2^62.
gmp: overflow in mpz type
Abort

从下面：

?- X is 2^2^36.
ERROR: Out of global stack
?- X is 2^2^37.
gmp: overflow in mpz type
Abort

因此,如果数字足够大,则SWI会检测到错误 – 因此可以由SWI处理(错误：消息来自SWI).

解决方法

不是答案,而是解释SWI-Prolog的作用.首先,它估计是否
可能会发生溢出.如果确定,在调用GMP之前会引发错误.否则,它
依赖于GMP分配挂钩并在失败时执行longjmp().它跟踪哪个
为什么分配和释放为中止的GMP操作分配的内存.它
因为记忆永远不会受到GMP的控制,所以可以这样做.成功的结果
GMP计算被复制到Prolog堆栈并受Prolog内存管理的约束.

这曾经有用,但在最近的版本中不起作用.我怀疑GMP估计的大小
如果它知道这将失败,甚至不打扰调用malloc()钩子.我所需要的只是一种方法,以确保始终调用钩子,即使有一个非常大的值.比size_t更大的所有东西都可以用(size_t)-1来调用钩子.

附：它比内存可以存储的更早溢出,因为复制到(较小的)Prolog运行时堆栈.

原文地址：https://www.jb51.cc/c/118672.html

c – GMP pow中的溢出处理

解决方法

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