Hi Dan,
Thanks for the report!
I'm a little surprised that this bug was not picked up during testing.
The try program specifically tests for all memory alignment
possibilities. I'll have to look into why it was not picked up.
Nonetheless, a bug is a bug. We'll sort this out before releasing MPIR 1.3.
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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