By the way, in the mean time, the following may be a workaround for you.
As allocation on non-limb aligned boundaries will imply a performance
penalty and throw off all the cycle counts for the highly optimised
MPIR assembly functions anyway, you may as well use a default x86_64
build if your memory allocator is not standard.
To use a "safe" default x86_64 build, use the following:
./configure --build=x86_64
Firstly I have to look into whether Jason intended these functions to
require limb boundary allocation, in which case the documentation will
be where the bug exists. I'll let you know when we figure out which
way this goes.
Bill.
2009/12/10 Dan Grayson <d...@math.uiuc.edu>:
> /*
>
> Bug in mpir 1.2.1.
>
> This program demonstrates that mpn_lshift, as implemented on 64 bit
> intel
> machines by mpn/x86_64/core2/lshift.as, gives the wrong answer if
> the limbs
> are not aligned to an 8 byte boundary.
>
> The confusion in the code starts with these lines:
>
> and r9, -16
> movdqa xmm3, [r9]
>
> In mpir 1.3.0-rc3, that file is gone, but the same faulty code
> lingers on in
> the following files, which may need attention:
>
> mpn/x86_64/k8/k10/lshift.as
> mpn/x86_64/atom/lshift.as
>
> Even if the default allocator always returns 8-byte aligned memory
> blocks,
> this is still a bug, because the documentation on "Custom
> Allocation"
> doesn't require custom memory allocators to obey any alignment
> requirements.
>
> Here's the output from the program
>
> 5285209847924392297689518137364380393182068736
> 5285209916707841180605126409194605050347913216
>
> Correct output would have the second line the same as the first.
>
> Linux fedora64 2.6.31.6-162.fc12.x86_64 #1 SMP Fri Dec 4 00:06:26
> EST 2009 x86_64 x86_64 x86_64 GNU/Linux
>
> gcc version 4.4.2 20091027 (Red Hat 4.4.2-7) (GCC)
>
> */
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <gmp.h>
> #include <assert.h>
>
> int main (int argc, char **argv) {
> mpz_t rp, sp;
> mpz_init2 (rp, 10 * 64);
> mpz_init2 (sp, 10 * 64);
> mpz_set_str (rp, "660651230990549037211189767170547549147758592",
> 10);
>
> mpz_set_str (sp, "660651230990549037211189767170547549147758592",
> 10);
> mpn_lshift (rp -> _mp_d, sp -> _mp_d, 3, 3);
> mpz_out_str(stdout, 10, rp);
> printf("\n");
>
> sp->_mp_d = (mp_limb_t *)((char *)sp->_mp_d + 4);
>
> mpz_set_str (sp, "660651230990549037211189767170547549147758592",
> 10);
> mpn_lshift (rp -> _mp_d, sp -> _mp_d, 3, 3);
> mpz_out_str(stdout, 10, rp);
> printf("\n");
>
> return 0;
> }
>
> --
>
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