refactor: take use of secp256k1_scalar_{zero,one} constants #1330

1. 
   theStack commented at 11:19 pm on May 29, 2023: contributor

   Rather than allocating a (non-constant) scalar variable on the stack with the sole purpose of setting it to a constant value, the global constants secp256k1_scalar_{zero,one} (apparently introduced in 34a67c773b0871e5797c7ab506d004e80911f120, PR #710) can be directly used instead for the values 0 or 1. There is very likely not even a difference in run-time, but it leads to simpler and less code which might be nice.
2. in src/tests.c:4639 in 94b85556a6 outdated

   4635@@ -4643,7 +4636,7 @@ static int ecmult_multi_false_callback(secp256k1_scalar *sc, secp256k1_ge *pt, s
   4636 
   4637 static void test_ecmult_multi(secp256k1_scratch *scratch, secp256k1_ecmult_multi_func ecmult_multi) {
   4638     int ncount;
   4639-    secp256k1_scalar szero;
   4640+    const secp256k1_scalar szero = secp256k1_scalar_zero;
   

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   real-or-random commented at 7:36 am on May 30, 2023:

   Why not get rid of szero entirely?

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   theStack commented at 10:28 am on May 30, 2023:

   Kept it due to some irrational “diff will get too large, lines will get too long” thoughts and a portion of laziness 😅 Done now.
3. in src/tests.c:1 in 94b85556a6

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   real-or-random commented at 7:38 am on May 30, 2023:

   Can you add tests that check that the constants match what you get with secp256k1_scalar_set_int?

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   theStack commented at 10:30 am on May 30, 2023:

   Thanks, done. Also put secp256k1_scalar_is_{zero,one} checks in.
4. 
   real-or-random commented at 7:38 am on May 30, 2023: contributor

   Concept ACK
5. refactor: take use of `secp256k1_scalar_{zero,one}` constants 654246c635
6. tests: add checks for scalar constants `secp256k1_scalar_{zero,one}` ade5b36701
7. theStack force-pushed on May 30, 2023
8. real-or-random approved
9. 
   real-or-random commented at 11:53 am on May 30, 2023: contributor

   utACK ade5b367018a624ff7ca1ecbb4a64889d47b0142
10. real-or-random added the label refactor on May 30, 2023
11. 
    sipa commented at 4:49 pm on May 31, 2023: contributor

    utACK ade5b367018a624ff7ca1ecbb4a64889d47b0142
12. real-or-random merged this on May 31, 2023
13. real-or-random closed this on May 31, 2023

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14. theStack deleted the branch on May 31, 2023
15. vmta referenced this in commit e1120c94a1 on Jun 4, 2023
16. sipa referenced this in commit 901336eee7 on Jun 21, 2023
17. vmta referenced this in commit 8f03457eed on Jul 1, 2023
18. hebasto referenced this in commit 270d2b37b8 on Jul 21, 2023
19. jonasnick cross-referenced this on Jul 26, 2023 from issue Upstream PRs 1314, 1317, 1318, 1316, 1327, 1310, 1328, 1333, 1330, 1334, 1337, 1341, 1339, 1350, 1349, 1338, 1129, 1347, 1336, 1295, 1354, 1355, 1356 by jonasnick
20. theStack cross-referenced this on Aug 1, 2023 from issue refactor: take use of `secp256k1_scalar_{zero,one}` constants (part 2) by theStack

Contributors
theStack real-or-random sipa

Labels
refactor/smell