Avoids a potentially shortening size_t to int cast in strauss_wnaf_ #841

1. 
   real-or-random commented at 1:57 pm on October 26, 2020: contributor

   Fixes #834.
2. sipa cross-referenced this on Oct 26, 2020 from issue gcc emits -Warray-bounds warnings by hebasto
3. 
   sipa commented at 7:47 pm on October 26, 2020: contributor

   I confirm this fixes the

    0In file included from src/secp256k1.c:16:
    1src/ecmult_impl.h: In function ‘secp256k1_ecmult.constprop’:
    2src/ecmult_impl.h:496:48: warning: array subscript [1, 268435456] is outside array bounds of ‘struct secp256k1_strauss_point_state[1]’ [-Warray-bounds]
    3  496 |             secp256k1_gej tmp = a[state->ps[np].input_pos];
    4      |                                   ~~~~~~~~~~~~~^~~~~~~~~~
    5src/ecmult_impl.h:565:42: note: while referencing ‘ps’
    6  565 |     struct secp256k1_strauss_point_state ps[1];
    7      |                                          ^~
    8src/ecmult_impl.h:502:139: warning: array subscript [1, 268435456] is outside array bounds of ‘struct secp256k1_strauss_point_state[1]’ [-Warray-bounds]
    9  502 |             secp256k1_fe_mul(state->zr + np * ECMULT_TABLE_SIZE(WINDOW_A), state->zr + np * ECMULT_TABLE_SIZE(WINDOW_A), &(a[state->ps[np].input_pos].z));
   10      |                                                                                                                              ~~~~~~~~~~~~~^~~~~~~~~~
   11src/ecmult_impl.h:565:42: note: while referencing ‘ps’
   12  565 |     struct secp256k1_strauss_point_state ps[1];
   

   warning.

4. 
   hebasto commented at 8:21 pm on October 26, 2020: member

   Tested f1c9131c798107efa4b2e660ae37b183ac662741 on Linux Mint 20 (x86_64):

   0$ gcc --version
   1gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0
   2Copyright (C) 2019 Free Software Foundation, Inc.
   3This is free software; see the source for copying conditions.  There is NO
   4warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
   5
   6$ make > /dev/null
   7# no warnings :)
   

5. 
   gmaxwell commented at 11:56 pm on October 26, 2020: contributor

   This looks reasonable to me.
6. Avoids a potentially shortening size_t to int cast in strauss_wnaf_

   Fixes #834.

   8893f42438
7. real-or-random force-pushed on Oct 27, 2020
8. real-or-random marked this as ready for review on Oct 27, 2020
9. 
   real-or-random commented at 1:19 am on October 27, 2020: contributor

   Ok, I didn’t expect that this will also fix the warning! Updated the commit message accordingly.
10. 
    sipa commented at 1:24 am on October 27, 2020: contributor

    Ok, I didn’t expect that this will also fix the warning! Updated the commit message accordingly.

    Bogus compiler warning acts bogusly.

11. 
    sipa commented at 1:27 am on October 27, 2020: contributor

    ACK 8893f42438ac75838a9dc7df7e98b29e9a1a085f. np and no shouldn’t ever take on negative values.
12. 
    jonasnick commented at 9:20 am on October 27, 2020: contributor

    ACK 8893f42438ac75838a9dc7df7e98b29e9a1a085f

    Also kicked travis since it hadn’t started the job.

13. 
    elichai commented at 10:06 am on October 27, 2020: contributor

    ACK 8893f42438ac75838a9dc7df7e98b29e9a1a085f Cool that it fixed the warning hehe
14. jonasnick merged this on Oct 27, 2020
15. jonasnick closed this on Oct 27, 2020

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16. 
    hebasto commented at 1:29 pm on October 27, 2020: member

    Is it planned to pull this change into the Bitcoin Core repo before 0.21.0 branching off?
17. 
    gmaxwell commented at 4:54 pm on October 27, 2020: contributor

    @hebasto You’re asking in the wrong place, other than sipa no one else here regularly contributes to bitcoin-core. :)
18. jasonbcox referenced this in commit 8f1b1aaef1 on Oct 27, 2020
19. deadalnix referenced this in commit 43bb9cebec on Oct 28, 2020

Contributors
real-or-random sipa hebasto gmaxwell jonasnick elichai