Utils and libraries: Leveldb compile warnings #12562

Warning messages:

leveldb/util/logging.cc: In function ‘bool leveldb::ConsumeDecimalNumber(leveldb::Slice*, uint64_t*)’:
leveldb/util/logging.cc:58:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
           (v == kMaxUint64/10 && delta > kMaxUint64%10)) {
                                  ~~~~~~^~~~~~~~~~~~~~~

leveldb/port/port_posix.cc: In function ‘bool leveldb::port::HasAcceleratedCRC32C()’:
leveldb/port/port_posix.cc:60:15: warning: ‘ecx’ may be used uninitialized in this function [-Wmaybe-uninitialized]
   return (ecx & (1 << 20)) != 0;
          ~~~~~^~~~~~~~~~~~

Fixes:

leveldb/port/port_posix.cc:60:15: warning: ‘ecx’ may be used uninitialized in this function

Code part:

  unsigned int eax, ebx, ecx, edx;
  ecx = 0;
  __get_cpuid(1, &eax, &ebx, &ecx, &edx);
  return (ecx & (1 << 20)) != 0;

Explanation: Simply initiated ecx variable.

ecx = 0; 

leveldb/util/logging.cc:58:40: warning: comparison between signed and unsigned integer expressions

Code part:

    if (c >= '0' && c <= '9') {
      ++digits;
      const int delta = (c - '0');
      static const uint64_t kMaxUint64 = ~static_cast<uint64_t>(0);
      if (v > kMaxUint64/10 ||
         (v == kMaxUint64/10 && (uint64_t) delta > kMaxUint64%10)) {
        // Overflow
        return false;
      }

Explanation: if statement comparing c >= '0' forces c to be definite positive or zero. 'delta' constant value assignment ( delta = (c - '0') ) and the comparison of it with a modular division also shows that 'delta' is definite positive or zero. So we can make an inline type change from int to uint64_t for 'delta' such that

(v == kMaxUint64/10 && (uint64_t) delta > kMaxUint64%10)) {

Hope I did PR correctly this time. CONTRIBUTING.md kinda confused me since explanation for upstream repository exists there.

Two comments:

• This is still in the wrong repository. Changes to LevelDB should go to the https://github.com/bitcoin-core/leveldb repository at least, and ideally through https://github.com/google/leveldb. We regularly pull in new versions from those repositories, but don't make local changes here directly.
• You seem to have added a number of unrelated files to the repository.

I just built upstream LevelDB (at commit 41172a24016bc29fc795ed504737392587f54e3d) and all of these have been fixed there.

OK. Thank you.