"Fossies" - the Fresh Open Source Software Archive

Member "perl-5.32.1/Porting/README.y2038" (18 Dec 2020, 3544 Bytes) of package /linux/misc/perl-5.32.1.tar.xz:


As a special service "Fossies" has tried to format the requested text file into HTML format (style: standard) with prefixed line numbers. Alternatively you can here view or download the uninterpreted source code file.

    1 The y2038 implementation for perl
    2 ===========================================================================
    3 This is an implementation of POSIX time.h which solves the year 2038 bug on
    4 systems where time_t is only 32 bits.  It is implemented in bog-standard
    5 ANSI C.  The latest version can be found at https://github.com/evalEmpire/y2038
    6 
    7 It makes use of the system's native 32 bit functions to perform time zone
    8 and daylight savings time calculations and thus does *not* need to ship its
    9 own time zone table.
   10 
   11 time64.h currently implements three public functions, localtime64_r(),
   12 gmtime64_r() and timegm64().  They are implementations of localtime_r(),
   13 gmtime_r() and timegm64().
   14 
   15 To install, simply copy time64.c and time64.h into your project and make
   16 use of the functions.
   17 
   18 To test, run "make test".  You must have Perl, prove (which comes with a
   19 recent version of the Test::Harness Perl module) and bzdiff installed to
   20 run the full test suite.  It will do a number of unit tests, plus test
   21 against a large table of known good values in different time zones.
   22 
   23 Limitations, Issues, etc...
   24 ---------------------------
   25 localtime64_r() gets its time zone and daylight savings time information by
   26 mapping the future year back to a similar one between 2010 and 2037, safe
   27 for localtime_r().  The calculations are accurate according to current time
   28 zone and daylight savings information, but may become inaccurate if a
   29 change is made that takes place after 2010.
   30 
   31 Future versions will probe for a 64 bit safe system localtime_r() and
   32 gmtime_r() and use that.
   33 
   34 The maximum date is still limited by your tm struct.  Most 32 bit systems
   35 use a signed integer tm_year which means the practical upper limit is the
   36 year 2147483647 which is somewhere around 2**54.  You can use a 64 bit
   37 clean tm struct by setting USE_TM64 in time64.h
   38 
   39 Portability
   40 -----------
   41 I would like to add some configuration detection stuff in the future, but
   42 for now all I can do is document the assumptions...
   43 
   44 This code assumes that long longs are 64 bit integers which is technically
   45 in violation of the C standard.  This can be changed in time64.h by
   46 changing the Time64_T and Int64 typedefs.
   47 
   48 There are a number of configuration options in time64.h.
   49 
   50 Configure variables
   51 -------------------
   52 Configure probes for the maximum and minimum values that gmtime () and
   53 localtime () accept on the local system. Configure however is only used on
   54 unix-like systems. For windows and VMS these values are hard-coded. You can
   55 use timecheck.c in the Porting directory to check those values yourself,
   56 using the same technique that is used in Configure based on bit-shifting:
   57 
   58   $ cd Porting
   59   $ cc -O -o timecheck timecheck.c
   60   $ ./timecheck
   61   ======================
   62   Sizeof time_t = 8
   63   gmtime () boundaries:
   64     8:  0x00f0c2ab7c54a97f:   2147485547-12-31 23:59:59
   65     8: -0x0000000e79747c00:            0-01-01 00:00:00
   66   localtime () boundaries:
   67     8:  0x00f0c2ab7c549b6f:   2147485547-12-31 23:59:59
   68     8: -0x0000000e79748094:            0-01-01 00:00:00
   69   Configure variables:
   70   sGMTIME_max='67768036191676799'
   71   sGMTIME_min='-62167219200'
   72   sLOCALTIME_max='67768036191673199'
   73   sLOCALTIME_min='-62167220372'
   74 
   75 In the rare case that your system uses a double for time_t, you can use the
   76 alternate approach to test for these values:
   77 
   78   $ cd perl/Porting
   79   $ cc -O -o timecheck2{,.c}
   80   $ ./timecheck2
   81                 gmtime max 67768036191676800
   82              localtime max 67768036191673200
   83                 gmtime min -67768040609740800
   84              localtime min -67768040609741968