On Thursday, 19 April 2012 11:33:36 UTC+8, Stephen Montgomery-Smith wrote:
>
> I think I have found the problem with sympow. It is nothing to do with
> elliptic curves. It is simply a malloc/free error.
>
> In util.c there is a function free_data, which frees TACKS[0]. TACKS[0]
> is meant to be allocated in disk.c, but there are circumstances when
> TACKS[0] is not allocated.
>
> See the attached patch.
>
> I am not going to submit it as a trac ticket until I have heard from
> others. In general, how to different OS's react to "free(NULL)"?
> FreeBSD does nothing, but maybe other OS's crash. In that case, the
> code in free_data will also need to be changed to something like "if
> (TACKS[0]!=NULL) free(TACKS[0]);".
>
MacOSX and Linux also don't do anything when free(NULL) is executed.
A problem might arise when the default OS's free() is substituted by
something else, e.g. a debugging version of malloc/free.
> But also, maybe there are other errors like this in sympow. I caught
> this one by chance.
>
It would be great if you provided steps to reproduce this bug.
It certainly is not caught by Sage doctests on MacOSX and Linux.
>
> --- sympow-1.018.1.p11/src/disk.c-orig 2012-04-19 02:33:51.000000000 +0000
> +++ sympow-1.018.1.p11/src/disk.c 2012-04-19 02:34:22.000000000 +0000
> @@ -39,7 +39,7 @@
> else if (((sp&3)==0) && CM_CASE) {if (2*ep==sp) S[3]='l'; else S[3]='h';}
> else {if (2*ep==sp) S[3]='L'; else S[3]='H';}
> if (HECKE && dv) {TACKS[which]=malloc(dv*sizeof(QD)); TACKON[which]=dv;}
> - else if (dv<=sp/2) TACKON[which]=0;
> + else if (dv<=sp/2) {TACKS[which]=NULL; TACKON[which]=0;}
> else {TACKS[which]=malloc((dv-sp/2)*sizeof(QD)); TACKON[which]=dv-sp/2;}
> S[4]=0; F=fopen("datafiles/param_data","r"); strcpy(U,S);
> if (ANAL_RANK) {if (dv>0) U[0]='A'; else U[0]='m';}
>
>
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