Fix bit packing and quantize on big endian.

[wengxt]

1. BitPackShift() doesn't return the right value on big endian for
   {Read,Write}Int25. Consecutive25 would just fail on big endian.
   The fix is to round it to 32 instead 64.

2. Using a WriteInt57 and Two ReadInt25 to read the combined integer value
   won't simply work on big endian. The fix just simply replace the
   WriteInt57 with two ReadInt25 for MiddlePointer.

[wengxt]

Some more context:
I use kenlm in https://github.com/fcitx/libime and some fedora packager notifies me about the issue on s390x cpu, so I tried to figure out what's going wrong there.

My test is done on a s390x platform provided by https://linuxone.cloud.marist.edu/.
This is a site that provides a free-120 day trail for s390x vps, just in case if you want to test the change.

[kpu]

Wow I had to admit testing on big endian hasn't actually happened.

[kpu]

With a tweak, we can avoid two memory accesses in the write.

        void Write(float prob, float backoff) const {
          uint64_t prob_encoded = (ProbBins().EncodeProb(prob));
          uint64_t backoff_encoded = BackoffBins().EncodeBackoff(backoff);
#if BYTE_ORDER == LITTLE_ENDIAN
          prob_encoded
#elif BYTE_ORDER == BIG_ENDIAN
          backoff_encoded
#endif
                  <<= BackoffBins().Bits();
          util::WriteInt57(address_.base, address_.offset, ProbBins().Bits() + BackoffBins().Bits(),
                           prob_encoded | backoff_encoded);
        }

[kpu]

Thanks, I've merged this and also fixed a test failure due to merge_test. There's still some endianness assumptions in https://github.com/kpu/kenlm/blob/master/lm/interpolate/bounded_sequence_encoding.hh which causes test failures but almost nobody uses interpolation.

[kpu]

Interpolation should be fixed too now, thanks for stopping by!