date: avoid "X years, 12 months" in relative dates

When relative dates are more than about a year ago, we start
writing them as "Y years, M months".  At the point where we
calculate Y and M, we have the time delta specified as a
number of days. We calculate these integers as:

  Y = days / 365
  M = (days % 365 + 15) / 30

This rounds days in the latter half of a month up to the
nearest month, so that day 16 is "1 month" (or day 381 is "1
year, 1 month").

We don't round the year at all, though, meaning we can end
up with "1 year, 12 months", which is silly; it should just
be "2 years".

Implement this differently with months of size

  onemonth = 365/12

so that

  totalmonths = (long)( (days + onemonth/2)/onemonth )
  years = totalmonths / 12
  months = totalmonths % 12

In order to do this without floats, we write the first formula as

  totalmonths = (days*12*2 + 365) / (365*2)

Tests and inspiration by Jeff King.

Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/date.c b/date.c
index 00f9eb5d0b9730107a8e08e92eb04d4cc9233595..896fbb48060c673b8dc2f2aa6ea3de3c1042fbd2 100644 (file)
--- a/date.c
+++ b/date.c
@@ -129,8 +129,9 @@ const char *show_date_relative(unsigned long time, int tz,
        }
        /* Give years and months for 5 years or so */
        if (diff < 1825) {
-               unsigned long years = diff / 365;
-               unsigned long months = (diff % 365 + 15) / 30;
+               unsigned long totalmonths = (diff * 12 * 2 + 365) / (365 * 2);
+               unsigned long years = totalmonths / 12;
+               unsigned long months = totalmonths % 12;
                int n;
                n = snprintf(timebuf, timebuf_size, "%lu year%s",
                                years, (years > 1 ? "s" : ""));

diff --git a/t/t0006-date.sh b/t/t0006-date.sh
index 1d4d0a5c7d2549c67334a8d5dd3f462962db81f2..f87abb5a0682d7a2fc7c3947789301c4157d331d 100755 (executable)
--- a/t/t0006-date.sh
+++ b/t/t0006-date.sh
@@ -25,6 +25,7 @@ check_show 37500000 '1 year, 2 months ago'
 check_show 55188000 '1 year, 9 months ago'
 check_show 630000000 '20 years ago'
 check_show 31449600 '12 months ago'
+check_show 62985600 '2 years ago'
 
 check_parse() {
        echo "$1 -> $2" >expect