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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)