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;;;; "time.scm" Posix time conversion routines
;;; Copyright (C) 1994 Aubrey Jaffer.
;
;Permission to copy this software, to redistribute it, and to use it
;for any purpose is granted, subject to the following restrictions and
;understandings.
;
;1. Any copy made of this software must include this copyright notice
;in full.
;
;2. I have made no warrantee or representation that the operation of
;this software will be error-free, and I am under no obligation to
;provide any services, by way of maintenance, update, or otherwise.
;
;3. In conjunction with products arising from the use of this
;material, there shall be no use of my name in any advertising,
;promotional, or sales literature without prior written consent in
;each case.
(define time:daylight 0)
(define *timezone* 0)
(define time:tzname #("GMT" "GDT"))
(define (time:tzset)
(set! time:daylight 1)
(set! *timezone* (* 5 60 60))
(set! time:tzname #("EST" "EDT")))
;;; No, it doesn't do leap seconds. If you want to add it, go ahead.
;;; Returns the `struct tm' representation of T,
;;; offset TM_GMTOFF seconds east of UCT.
(define (time:split t tm_isdst tm_gmtoff tm_zone)
(set! t (difftime t tm_gmtoff))
(let* ((days-in-year (lambda (year)
(if (and (zero? (remainder year 4))
(or (not (zero? (remainder year 100)))
(zero? (remainder year 400))))
366 365)))
(days/month #(#(31 28 31 30 31 30 31 31 30 31 30 31) ; Normal years.
#(31 29 31 30 31 30 31 31 30 31 30 31))) ; Leap years.
(SECS/HOUR (* 60 60))
(SECS/DAY (* SECS/HOUR 24))
(secs (modulo t SECS/DAY))
(days (+ (quotient t SECS/DAY)
(if (and (negative? t) (positive? secs)) -1 0))))
(let ((tm_hour (quotient secs SECS/HOUR))
(secs (remainder secs SECS/HOUR))
(tm_wday (modulo (+ 4 days) 7))) ; January 1, 1970 was a Thursday.
(let loop ((tm_year 1970)
(tm_yday days))
(let ((diy (days-in-year tm_year)))
(cond
((negative? tm_yday) (loop (+ -1 tm_year) (+ tm_yday diy)))
((>= tm_yday diy) (loop (+ 1 tm_year) (- tm_yday diy)))
(else
(let* ((mv (vector-ref days/month (- diy 365))))
(do ((tm_mon 0 (+ 1 tm_mon))
(tm_mday tm_yday (- tm_mday (vector-ref mv tm_mon))))
((< tm_mday (vector-ref mv tm_mon))
(vector
(remainder secs 60) ; Seconds. [0-61] (2 leap seconds)
(quotient secs 60) ; Minutes. [0-59]
tm_hour ; Hours. [0-23]
(+ tm_mday 1) ; Day. [1-31]
tm_mon ; Month. [0-11]
(- tm_year 1900) ; Year - 1900.
tm_wday ; Day of week. [0-6]
tm_yday ; Days in year. [0-365]
tm_isdst ; DST. [-1/0/1]
tm_gmtoff ; Seconds west of UTC.
tm_zone ; Timezone abbreviation.
)))))))))))
(define (time:gmtime t)
(time:split t 0 0 "GMT"))
(define (time:localtime t)
(time:tzset)
(time:split t time:daylight *timezone*
(vector-ref time:tzname time:daylight)))
(define time:year-70
(let* ((t (current-time)))
(offset-time (offset-time t (- (difftime t 0))) (* -70 32140800))))
(define (time:invert decoder target)
(let* ((times #(1 60 3600 86400 2678400 32140800))
(trough ; rough time for target
(do ((i 5 (+ i -1))
(trough time:year-70
(offset-time trough (* (vector-ref target i)
(vector-ref times i)))))
((negative? i) trough))))
;;; (print 'trough trough 'target target)
(let loop ((guess trough)
(j 0)
(guess-tm (decoder trough)))
;;; (print 'guess guess 'guess-tm guess-tm)
(do ((i 5 (+ i -1))
(rough time:year-70
(offset-time rough (* (vector-ref guess-tm i)
(vector-ref times i))))
(sign (let ((d (- (vector-ref target 5)
(vector-ref guess-tm 5))))
(and (not (zero? d)) d))
(or sign
(let ((d (- (vector-ref target i)
(vector-ref guess-tm i))))
(and (not (zero? d)) d)))))
((negative? i)
(let* ((distance (abs (- trough rough))))
(cond ((and (zero? distance) sign)
;;; (print "trying to jump")
(set! distance (if (negative? sign) -86400 86400)))
((and sign (negative? sign)) (set! distance (- distance))))
(set! guess (offset-time guess distance))
;;; (print 'distance distance 'sign sign)
(cond ((zero? distance) guess)
((> j 5) #f) ;to prevent inf loops.
(else
(loop guess
(+ 1 j)
(decoder guess))))))))))
(define (time:mktime time)
(time:tzset)
(time:invert localtime time))
(define (time:asctime decoded)
(let ((days #("Sun" "Mon" "Tue" "Wed" "Thu" "Fri" "Sat"))
(months #("Jan" "Feb" "Mar" "Apr" "May" "Jun"
"Jul" "Aug" "Sep" "Oct" "Nov" "Dec"))
(number->2digits
(lambda (n ch)
(set! n (number->string n))
(if (= 1 (string-length n))
(string-append ch n)
n))))
(string-append
(vector-ref days (vector-ref decoded 6)) " "
(vector-ref months (vector-ref decoded 4)) " "
(number->2digits (vector-ref decoded 3) " ") " "
(number->2digits (vector-ref decoded 2) "0") ":"
(number->2digits (vector-ref decoded 1) "0") ":"
(number->2digits (vector-ref decoded 0) "0") " "
(number->string (+ 1900 (vector-ref decoded 5)))
(string #\newline))))
(define (time:ctime time)
(time:asctime (time:localtime time)))
(define tzset time:tzset)
(define gmtime time:gmtime)
(define localtime time:localtime)
(define mktime time:mktime)
(define asctime time:asctime)
(define ctime time:ctime)
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