[Help-glpk] Time conversion functions

[xypron]

Hello Andrew,

currently I am using GLPK mainly for scheduling problems. Here the data
often contains references to time. The GMPL language does not provide any
functions to convert timestamps to numbers and numbers back to timestamps.

I propose to add the following functions:

now() returns the number of seconds since 1970
Knowing the current time is useful as scheduling should not place production
in the past.

str2time( str, fmt ) converts a timestamp str given in format fmt to number
of seconds since 1970
e.g. str2time( "2008-11-15T13:22:10+0300", "%Y-%m-%dT%H:%M:%S%z");
The time formats of RFC 3339 should be supported (a subset of ISO 8601).
The format strings should be a subset of those used by the strptime()
function in library GLIBC.
Conversion of non local time will have to rely on availability of either
function timegm() (or _mkgmtime for Microsoft Visual C) or structure element
tm->tm_gmtoff.

localtime( num, fmt ) converts a number to a timestamp in local time
e.g. localtime( now(), "%Y-%m-%dT%H:%M:%S%")
a possible output would be 
2008-11-15T17:22:10
The format strings should be those used by the strftime() function in C99.

gmtime( num, fmt ) converts a number to a timestamp in global time
e.g. gmtime( now(), "%Y-%m-%dT%H:%M:%S%Z")
a possibel output would be
2008-11-15T16:22:10
The format strings should be those used by the strftime() function in C99.

I have implemented the necessary changes to glpk-4.33 which can be found at 
http://glpk.dyndns.org/viewvc/svn/glpk/glpk/branches/glpk-4.33-strdate/
http://glpk.dyndns.org/viewvc/svn/glpk/glpk/branches/glpk-4.33-strdate/ 

new files are:
include/glptime.h
src/glptime.c

changed files are:
configure.ac
config.h.in
include/glpmpl.h
src/Makefile.am
src/glpmpl01.c
src/glpmpl03.c
w32/Makefile*
w32/config_VC9
w64/Makefile*
w64/config_VC9

Best regards

Xypron

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