gcc warning in range_totient

[hvds]

gcc-9 complains about args to memset() in range_totient() from latest master:

% gcc-9 --version | head -1
gcc-9 (Ubuntu 9.2.1-17ubuntu1~18.04.1) 9.2.1 20191102
...
gcc-9 -c   -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -g -O6   -DVERSION=\"0.73\" -DXS_VERSION=\"0.73\" -fPIC "-I/opt/mathsg-5.43.6/lib/perl5/5.43.6/x86_64-linux/CORE"   totients.c
In file included from /usr/include/string.h:494,
                 from totients.c:3:
In function 'memset',
    inlined from 'range_totient' at totients.c:91:5:
/usr/include/x86_64-linux-gnu/bits/string_fortified.h:71:10: warning: '__builtin_memset' specified bound 18446744073709551608 exceeds maximum object size 9223372036854775807 [-Wstringop-overflow=]
   71 |   return __builtin___memset_chk (__dest, __ch, __len, __bos0 (__dest));
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The memset() was introduced in 7f6602e to replace a Newz() which probably had the same overflow potential.

[danaj]

This: "bound 18446744073709551608 exceeds maximum object size 9223372036854775807" makes it look like "New" changes the type from UV to a signed type, hence the complaint. It looks like it should be Size_t though, so not sure why we're seeing this.

There is a problem in both the XS and C code if lo=0 and hi=UV_MAX. In 64-bit this is obviously never going to work, but we need to handle it more graciously.

We also have an issue in that EXTEND uses a signed type [SSize_t in 5.20+, int in previous]. In 64-bit this is a pathological case (but we still need to handle it). In 32-bit it's limiting. That is, in some cases the maximum size of the return list back to Perl is smaller than what we can safely calculate in C.

[danaj]

Hopefully this fixes the warning. We go back to using Newz in this case, hopefully making gcc see that the memset can't be larger than the allocation. It might also be smart enough to track the range after the check that count <= max signed size_t.

[danaj]

Building with gcc-14 on MacOS, using the same '-fwrapv -fno-strict-aliasing -fstack-protector-strong -Wall' flags doesn't show any warnings with the current code.

[hvds]

Thanks, confirmed clean with gcc-9 at c8af52a.