Improve struct tm population

Using Zeller's congruence to fill the day of week field,
Also populate the day of year field.

Add unit test to cover a number of cases.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3999)

crypto/asn1/a_time.c

@@ -31,6 +31,38 @@ static int leap_year(const int year)
     return 0;
 }
 
+/*
+ * Compute the day of the week and the day of the year from the year, month
+ * and day.  The day of the year is straightforward, the day of the week uses
+ * a form of Zeller's congruence.  For this months start with March and are
+ * numbered 4 through 15.
+ */
+static void determine_days(struct tm *tm)
+{
+    static const int ydays[12] = {
+        0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334
+    };
+    int y = tm->tm_year + 1900;
+    int m = tm->tm_mon;
+    int d = tm->tm_mday;
+    int c;
+
+    tm->tm_yday = ydays[m] + d - 1;
+    if (m >= 2) {
+        /* March and onwards can be one day further into the year */
+        tm->tm_yday += leap_year(y);
+        m += 2;
+    } else {
+        /* Treat January and February as part of the previous year */
+        m += 14;
+        y--;
+    }
+    c = y / 100;
+    y %= 100;
+    /* Zeller's congruance */
+    tm->tm_wday = (d + (13 * m) / 5 + y + y / 4 + c / 4 + 5 * c + 6) % 7;
+}
+
 int asn1_time_to_tm(struct tm *tm, const ASN1_TIME *d)
 {
     static const int min[9] = { 0, 0, 1, 1, 0, 0, 0, 0, 0 };
@@ -127,6 +159,7 @@ int asn1_time_to_tm(struct tm *tm, const ASN1_TIME *d)
             if (n > md)
                 goto err;
             tmp.tm_mday = n;
+            determine_days(&tmp);
             break;
         case 4:
             tmp.tm_hour = n;

doc/man3/ASN1_TIME_set.pod

@@ -55,10 +55,10 @@ an error.
 
 ASN1_TIME_to_tm() converts the time B<s> to the standard B<tm> structure.
 If B<s> is NULL, then the current time is converted. The output time is GMT.
-The B<tm_sec>, B<tm_min>, B<tm_hour>, B<tm_mday>, B<tm_mon> and B<tm_year>
+The B<tm_sec>, B<tm_min>, B<tm_hour>, B<tm_mday>, B<tm_wday>, B<tm_yday>,
-fields of B<tm> structure are set to proper values, whereas all other fields
+B<tm_mon> and B<tm_year> fields of B<tm> structure are set to proper values,
-are set to 0. If B<tm> is NULL this function performs a format check on B<s>
+whereas all other fields are set to 0. If B<tm> is NULL this function performs
-only.
+a format check on B<s> only.
 
 ASN1_TIME_diff() sets B<*pday> and B<*psec> to the time difference between
 B<from> and B<to>. If B<to> represents a time later than B<from> then

test/x509_time_test.c

@@ -345,9 +345,89 @@ out:
     return rv;
 }
 
+static const struct {
+    int y, m, d;
+    int yd, wd;
+} day_of_week_tests[] = {
+    /*YYYY  MM  DD  DoY  DoW */
+    { 1900,  1,  1,   0, 1 },
+    { 1900,  2, 28,  58, 3 },
+    { 1900,  3,  1,  59, 4 },
+    { 1900, 12, 31, 364, 1 },
+    { 1901,  1,  1,   0, 2 },
+    { 1970,  1,  1,   0, 4 },
+    { 1999,  1, 10,   9, 0 },
+    { 1999, 12, 31, 364, 5 },
+    { 2000,  1,  1,   0, 6 },
+    { 2000,  2, 28,  58, 1 },
+    { 2000,  2, 29,  59, 2 },
+    { 2000,  3,  1,  60, 3 },
+    { 2000, 12, 31, 365, 0 },
+    { 2001,  1,  1,   0, 1 },
+    { 2008,  1,  1,   0, 2 },
+    { 2008,  2, 28,  58, 4 },
+    { 2008,  2, 29,  59, 5 },
+    { 2008,  3,  1,  60, 6 },
+    { 2008, 12, 31, 365, 3 },
+    { 2009,  1,  1,   0, 4 },
+    { 2011,  1,  1,   0, 6 },
+    { 2011,  2, 28,  58, 1 },
+    { 2011,  3,  1,  59, 2 },
+    { 2011, 12, 31, 364, 6 },
+    { 2012,  1,  1,   0, 0 },
+    { 2019,  1,  2,   1, 3 },
+    { 2019,  2,  2,  32, 6 },
+    { 2019,  3,  2,  60, 6 },
+    { 2019,  4,  2,  91, 2 },
+    { 2019,  5,  2, 121, 4 },
+    { 2019,  6,  2, 152, 0 },
+    { 2019,  7,  2, 182, 2 },
+    { 2019,  8,  2, 213, 5 },
+    { 2019,  9,  2, 244, 1 },
+    { 2019, 10,  2, 274, 3 },
+    { 2019, 11,  2, 305, 6 },
+    { 2019, 12,  2, 335, 1 },
+    { 2020,  1,  2,   1, 4 },
+    { 2020,  2,  2,  32, 0 },
+    { 2020,  3,  2,  61, 1 },
+    { 2020,  4,  2,  92, 4 },
+    { 2020,  5,  2, 122, 6 },
+    { 2020,  6,  2, 153, 2 },
+    { 2020,  7,  2, 183, 4 },
+    { 2020,  8,  2, 214, 0 },
+    { 2020,  9,  2, 245, 3 },
+    { 2020, 10,  2, 275, 5 },
+    { 2020, 11,  2, 306, 1 },
+    { 2020, 12,  2, 336, 3 }
+};
+
+static int test_days(int n)
+{
+    char d[16];
+    ASN1_TIME *a = NULL;
+    struct tm t;
+    int r;
+
+    BIO_snprintf(d, sizeof(d), "%04d%02d%02d050505Z",
+                 day_of_week_tests[n].y, day_of_week_tests[n].m,
+                 day_of_week_tests[n].d);
+
+    if (!TEST_ptr(a = ASN1_TIME_new()))
+        return 0;
+
+    r = TEST_true(ASN1_TIME_set_string(a, d))
+        && TEST_true(ASN1_TIME_to_tm(a, &t))
+        && TEST_int_eq(t.tm_yday, day_of_week_tests[n].yd)
+        && TEST_int_eq(t.tm_wday, day_of_week_tests[n].wd);
+
+    ASN1_TIME_free(a);
+    return r;
+}
+
 void register_tests()
 {
     ADD_TEST(test_x509_cmp_time_current);
     ADD_ALL_TESTS(test_x509_cmp_time, OSSL_NELEM(x509_cmp_tests));
     ADD_ALL_TESTS(test_x509_time, OSSL_NELEM(x509_format_tests));
+    ADD_ALL_TESTS(test_days, OSSL_NELEM(day_of_week_tests));
 }