BSD 4_3_Net_2 release

[unix-history] / usr / src / usr.bin / cal / README

diff --git a/usr/src/usr.bin/cal/README b/usr/src/usr.bin/cal/README
index 89594dc..638ac9d 100644 (file)
--- a/usr/src/usr.bin/cal/README
+++ b/usr/src/usr.bin/cal/README
@@ -1,23 +1,13 @@
-Program Design
-
-This program exactly duplicates the operation of the original unix "cal"
-program.  It was designed with that intent, so no "improvements" were made
-to either the command line syntax or to the error reporting.  The main
-goal was to allow replacement of the existing binary with a freely
-redistibutable version without breaking any existing applications that
-might be built on top of the original.
-
-The date routines were written from scratch, basically from first
+The cal(1) date routines were written from scratch, basically from first

 principles.  The algorithm for calculating the day of week from any
 principles.  The algorithm for calculating the day of week from any

-gregorian date was "reverse engineered". This was necessary as most of
+Gregorian date was "reverse engineered".  This was necessary as most of

 the documented algorithms have to do with date calculations for other
 calendars (e.g. julian) and are only accurate when converted to gregorian
 within a narrow range of dates.
 
 the documented algorithms have to do with date calculations for other
 calendars (e.g. julian) and are only accurate when converted to gregorian
 within a narrow range of dates.
 

-I take 1 jan 1 to be a Saturday because that's what cal says and I couldn't
-change that even if I was dumb enough to try. From this we can easily
-calculate the day of week for any date. The algorithm for a zero based
-day of week:
+1 Jan 1 is a Saturday because that's what cal says and I couldn't change
+that even if I was dumb enough to try.  From this we can easily calculate
+the day of week for any date.  The algorithm for a zero based day of week:

 
        calculate the number of days in all prior years (year-1)*365
        add the number of leap years (days?) since year 1 
 
        calculate the number of days in all prior years (year-1)*365
        add the number of leap years (days?) since year 1 


@@ -39,17 +29,14 @@ day of week:
                just before taking the modulo.
 
 It must be noted that the number of leap years calculation is sensitive
                just before taking the modulo.
 
 It must be noted that the number of leap years calculation is sensitive

-to the date for which the leap year is being calculated. A year that occurs
+to the date for which the leap year is being calculated.  A year that occurs

 before the reformation is determined to be a leap year if its modulo of
 before the reformation is determined to be a leap year if its modulo of

-4 equals zero. But after the reformation, a year is only a leap year if
-its modulo of 4 equals zero and its modulo of 100 does not. Of course,
-there is an exception for these century years. If the modulo of 400 equals
-zero, then the year is a leap year anyway. This is, in fact, what the
+4 equals zero.  But after the reformation, a year is only a leap year if
+its modulo of 4 equals zero and its modulo of 100 does not.  Of course,
+there is an exception for these century years.  If the modulo of 400 equals
+zero, then the year is a leap year anyway.  This is, in fact, what the

 gregorian reformation was all about (a bit of error in the old algorithm
 that caused the calendar to be inaccurate.)
 
 Once we have the day in year for the first of the month in question, the
 gregorian reformation was all about (a bit of error in the old algorithm
 that caused the calendar to be inaccurate.)
 
 Once we have the day in year for the first of the month in question, the

-rest is trivial. Running diff on any output of this program and the
-equivalent output from the original cal reports no difference.  This was
-confirmed by a script that ran them for all possible inputs (and took
-approximately 36 hours to complete on a sun-3.)
+rest is trivial.