Somewhere between ccversion='16.00.30319.01' and ccversion='19.24.28316' a significant change in the MS C runtime occurred.

Sorry, I only have installed Visual studio 2017 and 2019 on my server. most of time I've used strawberry perl.

I only have installed Visual studio 2017 and 2019 on my server

I was expecting that a perl built with Visual Studio 2017 would report a $Config{ccversion} that was less than '19.24.28316' and greater than '16.00.30319.01'. (My guess is that with Visual Studio 2017, $Config{ccversion} would begin with 19.1...)
I thought that '19.24.28316' identifies Visual Studio 2019 and that '16.00.30319.01' identifies Visual Studio 2010.

Anyway, if you have a perl (whose ivsize is 8) that has been built with that Visual Studio 2017 compiler, and could test List::Uniqnum that would be handy.
Or, alternatively, just provide the output of perl -le "printf '%0.20g', 18446744073709549568;".
That output will also tell me whether '%0.20g' formatting is reliable or not - and the thing I'm trying to work out is at which version of the Microsoft compilers did '%0.20g' become reliable.
If it outputs 18446744073709549568, then '%0.20g' formatting is fine ... but not so if it outputs 18446744073709550000.

Cheers,
Rob

Here is the test:

C:\visperl\bin>perl -V
Summary of my perl5 (revision 5 version 30 subversion 1) configuration
+:

  Platform:
    osname=MSWin32
    osvers=10.0.17763.1039
    archname=MSWin32-x64-multi-thread
    uname=''
    config_args='undef'
    hint=recommended
    useposix=true
    d_sigaction=undef
    useithreads=define
    usemultiplicity=define
    use64bitint=define
    use64bitall=undef
    uselongdouble=undef
    usemymalloc=n
    default_inc_excludes_dot=define
    bincompat5005=undef
  Compiler:
    cc='cl'
    ccflags ='-nologo -GF -W3 -O1 -MD -Zi -DNDEBUG -GL -fp:precise -DW
+IN32 -D_CONSOLE -DNO_STRICT -DWIN64 -DCONSERVATIVE -D_CRT_SECURE_NO_D
+EPRECATE -D_CRT_NONSTDC_NO_DEPRECATE -D_WINSOCK_DEPRECATED_NO_WARNING
+S  -DPERL_TEXTMODE_SCRIPTS -DPERL_IMPLICIT_CONTEXT -DPERL_IMPLICIT_SY
+S'
    optimize='-O1 -MD -Zi -DNDEBUG -GL -fp:precise'
    cppflags='-DWIN32'
    ccversion='19.16.27024.1'
    gccversion=''
    gccosandvers=''
    intsize=4
    longsize=4
    ptrsize=8
    doublesize=8
    byteorder=12345678
    doublekind=3
    d_longlong=undef
    longlongsize=8
    d_longdbl=define
    longdblsize=8
    longdblkind=0
    ivtype='__int64'
    ivsize=8
    nvtype='double'
    nvsize=8
    Off_t='__int64'
    lseeksize=8
    alignbytes=8
    prototype=define
  Linker and Libraries:
    ld='link'
    ldflags ='-nologo -nodefaultlib -debug -opt:ref,icf -ltcg  -libpat
+h:"c:\visperl\lib\CORE"  -machine:AMD64 -subsystem:console,"5.02"'
    libpth="C:\Program Files (x86)\Microsoft Visual Studio\2017\Commun
+ity\VC\Tools\MSVC\14.16.27023\\lib\x64"
    libs=oldnames.lib kernel32.lib user32.lib gdi32.lib winspool.lib  
+comdlg32.lib advapi32.lib shell32.lib ole32.lib oleaut32.lib  netapi3
+2.lib uuid.lib ws2_32.lib mpr.lib winmm.lib  version.lib odbc32.lib o
+dbccp32.lib comctl32.lib msvcrt.lib vcruntime.lib ucrt.lib
    perllibs=oldnames.lib kernel32.lib user32.lib gdi32.lib winspool.l
+ib  comdlg32.lib advapi32.lib shell32.lib ole32.lib oleaut32.lib  net
+api32.lib uuid.lib ws2_32.lib mpr.lib winmm.lib  version.lib odbc32.l
+ib odbccp32.lib comctl32.lib msvcrt.lib vcruntime.lib ucrt.lib
    libc=ucrt.lib
    so=dll
    useshrplib=true
    libperl=perl530.lib
    gnulibc_version=''
  Dynamic Linking:
    dlsrc=dl_win32.xs
    dlext=dll
    d_dlsymun=undef
    ccdlflags=' '
    cccdlflags=' '
    lddlflags='-dll -nologo -nodefaultlib -debug -opt:ref,icf -ltcg  -
+libpath:"c:\visperl\lib\CORE"  -machine:AMD64 -subsystem:console,"5.0
+2"'


Characteristics of this binary (from libperl):
  Compile-time options:
    HAS_TIMES
    HAVE_INTERP_INTERN
    MULTIPLICITY
    PERLIO_LAYERS
    PERL_COPY_ON_WRITE
    PERL_DONT_CREATE_GVSV
    PERL_IMPLICIT_CONTEXT
    PERL_IMPLICIT_SYS
    PERL_MALLOC_WRAP
    PERL_OP_PARENT
    PERL_PRESERVE_IVUV
    USE_64_BIT_INT
    USE_ITHREADS
    USE_LARGE_FILES
    USE_LOCALE
    USE_LOCALE_COLLATE
    USE_LOCALE_CTYPE
    USE_LOCALE_NUMERIC
    USE_LOCALE_TIME
    USE_PERLIO
    USE_PERL_ATOF
    USE_THREAD_SAFE_LOCALE
  Built under MSWin32
  Compiled at Feb 24 2020 12:20:14
  @INC:
    C:/visperl/site/lib
    C:/visperl/lib
[download]

C:\visperl\bin>perl -le "printf '%0.20g', 18446744073709549568;"
18446744073709549568
[download]





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