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Witold Filipczyk 172c32a64c [cpp] All files suspected for any C++ relation renamed to cpp
Now (in meson) .c files are compiled by C compiler and .cpp by C++ compiler.
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auth [auth] const in add_auth_entry 2022-02-17 20:33:16 +01:00
bittorrent [bittorrent] signed char is not sufficient for va_arg 2022-06-23 21:39:11 +02:00
file [dgi] Unification. 2022-07-14 22:29:24 +02:00
finger [c] More fixes related to redefined PF_INET 2021-12-22 16:27:29 +01:00
fsp [network] enum connection_basic_state -> connection_basic_state_T 2022-01-28 16:25:40 +01:00
ftp [Makefile] DRY 2022-06-05 14:25:25 +02:00
gemini [gemini] changed declaration 2022-02-21 16:56:21 +01:00
gopher [gopher] const format 2022-02-21 17:15:48 +01:00
http [isspace] Some implementations of isspace require unsigned char 2022-06-28 20:25:06 +02:00
nntp [options] No need for C_ macro in INIT_OPT_* 2022-03-02 19:02:47 +01:00
rewrite [options] No need for C_ macro in INIT_OPT_* 2022-03-02 19:02:47 +01:00
smb [auth] cast 2022-01-26 17:21:42 +01:00
test [Makefile] DRY 2022-06-05 14:25:25 +02:00
Makefile [cpp] All files suspected for any C++ relation renamed to cpp 2022-07-31 16:44:11 +02:00
README.timegm Move README.timegm to the same directory as date.c. 2007-01-13 10:01:51 +02:00
about.c [about] const 2022-02-02 18:53:51 +01:00
about.h [mozjs24] Allow build elinks with g++ 2020-10-05 20:14:55 +02:00
common.c [protocol] const info 2022-02-17 20:50:05 +01:00
common.h [mozjs24] Allow build elinks with g++ 2020-10-05 20:14:55 +02:00
data.c [data] const type 2022-02-21 17:52:17 +01:00
data.h [mozjs24] Allow build elinks with g++ 2020-10-05 20:14:55 +02:00
date.c [time.h] time.h can be included unconditionally 2021-03-19 14:22:04 +01:00
date.h [cflags] Removed -Wno-pointer-sign 2021-01-02 16:20:27 +01:00
header.c [http] const in get_header_param 2022-02-17 20:39:07 +01:00
header.h [http] const in get_header_param 2022-02-17 20:39:07 +01:00
meson.build [cpp] All files suspected for any C++ relation renamed to cpp 2022-07-31 16:44:11 +02:00
protocol.cpp [cpp] All files suspected for any C++ relation renamed to cpp 2022-07-31 16:44:11 +02:00
protocol.h [dgi] Experimental DGI support. 2022-05-21 18:18:55 +02:00
proxy.c [protocol] more const in get_protocol_proxy 2022-02-17 20:22:29 +01:00
proxy.h [mozjs24] Allow build elinks with g++ 2020-10-05 20:14:55 +02:00
uri.c [protocol] Added option protocol.default_protocol . Refs #174 2022-06-14 18:43:09 +02:00
uri.h [cache] const in redirect_cache 2022-02-21 17:13:14 +01:00
user.c [options] No need for C_ macro in INIT_OPT_* 2022-03-02 19:02:47 +01:00
user.h [cache] const in redirect_cache 2022-02-21 17:13:14 +01:00

README.timegm

This file contains description of our my_timegm() function in date.c. It was
posted as a mail to links-list by Stephane Chazelas, and I thought it may be
interesting for someone, so I decided to include it in the ELinks distribution.




Un explanation for it as one (me to start with) may wonder why
this works.

We first change of calendar. To make things easy, let's say
that 0/0/0 0:0:0 in our new calendar is the Marsh 1st 1968, so
just after a february 29th as 1968 was a leap year.

if y/m/d h:min:s is time in our calendar
and
   Y/M/D h:min:s in the new calendar

M = m - 1 - 2 (+ 12 if m < 3)
Y = y - 68 (-1 if m < 3)
D = d - 1

at Y/0/0 0:0:0, there has been Y / 4 leap years in the past, so
(int) 365 * Y + Y / 4 days have past.

at Y/M/0 0:0:0, lets find how many days have past since Y/0/0:

                   |Mar                                        Feb
                  M| 0   1   2   3   4   5   6   7   8   9  10  11
-------------------+-----------------------------------------------
 days in that month|31  30  31  30  31  31  30  31  30  31  31  28 or 29
-------------------+-----------------------------------------------
  x = days at Y/M/0| 0  31  61  92 122 153 184 214 245 275 306 337
-------------------+-----------------------------------------------
first approximation|
         y = 30 * M| 0  30  60  90 120 150 180 210 240 270 300 330
-------------------+-----------------------------------------------
              x - y| 0   1   1   2   2   3   4   4   5   5   6   7
-------------------+-----------------------------------------------
(M + 4) * 3 / 5 - 2| 0   1   1   2   2   3   4   4   5   5   6   7
-------------------+-----------------------------------------------

x - y = (M + 4) * 3 / 5 - 2

x = 30 * M + (M + 4) * 3 / 5 - 2

x = (153 * M + 2) / 5

So at Y/M/D 0:0:0,

Y * 1461 / 4 + (153 * M + 2) / 5 + D days have past since
the 1st of March of 1968

1st of March of 1968 was 671 days before 1970 Jan 1st (year 0
for unix time())

So
t = s + 60 * (min + 60 * (h + 24 * (Y * 1461 / 4 + (153 * M + 2) / 5 + D - 671)))
t = s + 60 * (min + 60 * (h + 24 * (Y * 1461 / 4 + (153 * M + 2) / 5 + d - 672)))

This shouldn't work past 2100/02/28 23:59:59 as 2100 is not a leap year.

--
St<E9>phane