"implicit conversion loses integer precision" warnings

[hebasto]

When building with clang and the -Wshorten-64-to-32 flag, there are some warnings:

In file included from /home/hebasto/git/secp256k1/secp256k1/src/secp256k1.c:27:
In file included from /home/hebasto/git/secp256k1/secp256k1/src/field_impl.h:14:
In file included from /home/hebasto/git/secp256k1/secp256k1/src/field_5x52_impl.h:13:
/home/hebasto/git/secp256k1/secp256k1/src/modinv64_impl.h:279:39: warning: implicit conversion loses integer precision: 'uint64_t' (aka 'unsigned long') to 'uint32_t' (aka 'unsigned int') [-Wshorten-64-to-32]
  279 |             w = (f * g * (f * f - 2)) & m;
      |               ~ ~~~~~~~~~~~~~~~~~~~~~~^~~
/home/hebasto/git/secp256k1/secp256k1/src/modinv64_impl.h:289:19: warning: implicit conversion loses integer precision: 'uint64_t' (aka 'unsigned long') to 'uint32_t' (aka 'unsigned int') [-Wshorten-64-to-32]
  289 |             w = f + (((f + 1) & 4) << 1);
      |               ~ ~~^~~~~~~~~~~~~~~~~~~~~~
/home/hebasto/git/secp256k1/secp256k1/src/modinv64_impl.h:290:26: warning: implicit conversion loses integer precision: 'uint64_t' (aka 'unsigned long') to 'uint32_t' (aka 'unsigned int') [-Wshorten-64-to-32]
  290 |             w = (-w * g) & m;
      |               ~ ~~~~~~~~~^~~
/home/hebasto/git/secp256k1/secp256k1/src/modinv64_impl.h:370:39: warning: implicit conversion loses integer precision: 'uint64_t' (aka 'unsigned long') to 'uint32_t' (aka 'unsigned int') [-Wshorten-64-to-32]
  370 |             w = (f * g * (f * f - 2)) & m;
      |               ~ ~~~~~~~~~~~~~~~~~~~~~~^~~
/home/hebasto/git/secp256k1/secp256k1/src/modinv64_impl.h:380:19: warning: implicit conversion loses integer precision: 'uint64_t' (aka 'unsigned long') to 'uint32_t' (aka 'unsigned int') [-Wshorten-64-to-32]
  380 |             w = f + (((f + 1) & 4) << 1);
      |               ~ ~~^~~~~~~~~~~~~~~~~~~~~~
/home/hebasto/git/secp256k1/secp256k1/src/modinv64_impl.h:381:26: warning: implicit conversion loses integer precision: 'uint64_t' (aka 'unsigned long') to 'uint32_t' (aka 'unsigned int') [-Wshorten-64-to-32]
  381 |             w = (-w * g) & m;
      |               ~ ~~~~~~~~~^~~
In file included from /home/hebasto/git/secp256k1/secp256k1/src/secp256k1.c:28:
In file included from /home/hebasto/git/secp256k1/secp256k1/src/scalar_impl.h:20:
/home/hebasto/git/secp256k1/secp256k1/src/scalar_4x64_impl.h:119:42: warning: implicit conversion loses integer precision: 'uint64_t' (aka 'unsigned long') to 'int' [-Wshorten-64-to-32]
  119 |     overflow = secp256k1_u128_to_u64(&t) + secp256k1_scalar_check_overflow(r);
      |              ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/hebasto/git/secp256k1/secp256k1/src/scalar_4x64_impl.h:682:34: warning: implicit conversion loses integer precision: 'uint64_t' (aka 'unsigned long') to 'unsigned int' [-Wshorten-64-to-32]
  682 |     secp256k1_scalar_reduce(r, c + secp256k1_scalar_check_overflow(r));
      |     ~~~~~~~~~~~~~~~~~~~~~~~    ~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/hebasto/git/secp256k1/secp256k1/src/secp256k1.c:30:
/home/hebasto/git/secp256k1/secp256k1/src/ecmult_impl.h:518:21: warning: implicit conversion loses integer precision: 'size_t' (aka 'unsigned long') to 'int' [-Wshorten-64-to-32]
  518 |     for (i = n_wnaf - 1; i >= 0; i--) {
      |            ~ ~~~~~~~^~~
/home/hebasto/git/secp256k1/secp256k1/src/ecmult_impl.h:562:52: warning: implicit conversion loses integer precision: 'long' to 'int' [-Wshorten-64-to-32]
  562 |         for(j = ECMULT_TABLE_SIZE(bucket_window+2) - 1; j > 0; j--) {
      |               ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~
In file included from /home/hebasto/git/secp256k1/secp256k1/src/secp256k1.c:32:
In file included from /home/hebasto/git/secp256k1/secp256k1/src/ecmult_gen_impl.h:14:
/home/hebasto/git/secp256k1/secp256k1/src/hash_impl.h:151:52: warning: implicit conversion loses integer precision: 'uint64_t' (aka 'unsigned long') to 'uint32_t' (aka 'unsigned int') [-Wshorten-64-to-32]
  151 |     secp256k1_write_be32(&sizedesc[0], hash->bytes >> 29);
      |     ~~~~~~~~~~~~~~~~~~~~               ~~~~~~~~~~~~^~~~~
/home/hebasto/git/secp256k1/secp256k1/src/hash_impl.h:152:52: warning: implicit conversion loses integer precision: 'uint64_t' (aka 'unsigned long') to 'uint32_t' (aka 'unsigned int') [-Wshorten-64-to-32]
  152 |     secp256k1_write_be32(&sizedesc[4], hash->bytes << 3);
      |     ~~~~~~~~~~~~~~~~~~~~               ~~~~~~~~~~~~^~~~
/home/hebasto/git/secp256k1/secp256k1/src/hash_impl.h:261:19: warning: implicit conversion loses integer precision: 'size_t' (aka 'unsigned long') to 'int' [-Wshorten-64-to-32]
  261 |         int now = outlen;
      |             ~~~   ^~~~~~
13 warnings generated.

[real-or-random]

When building with clang and the -Wshorten-64-to-32 flag, there are some warnings:

Well, then don't use this flag. :P Or do you think this is a problem? Is it a default flag?

[hebasto]

Or do you think this is a problem?

Each case has to be investigated to answer this question.

Is it a default flag?

macOS Xcode set it by default.