From b75e3342a11ad24bdffef31cee01ad8582bbc0c9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Radom=C3=ADr=20Pol=C3=A1ch?= <rp@t4d.cz>
Date: Fri, 8 Nov 2024 21:12:09 +0100
Subject: [PATCH] change: generate field now do */n, m/n repeats

---
 ccronexpr.c      | 42 +++++++++++++++++++++++++++++-------------
 ccronexpr_test.c |  3 +++
 2 files changed, 32 insertions(+), 13 deletions(-)

diff --git a/ccronexpr.c b/ccronexpr.c
index edf95ac..e33b9d3 100644
--- a/ccronexpr.c
+++ b/ccronexpr.c
@@ -585,21 +585,37 @@ static int do_nextprev(cron_expr* expr, struct tm* calendar, int dot, int offset
 
 static int generate_field(char *dest, uint8_t *bits, int min, int max, int offset, int buffer_len) {
     char buf[32];
-    int first = 1, from = -1, len = 0, i, bit;
-
-    for (i = min; i <= max; i++) {
-        bit = (i < max) ? cron_get_bit(bits, i + offset) : 0;
-        if (bit) { if (from == -1) from = i; }
-        else if (from != -1) {
-            if (!first) STRCATC(dest, ",", 1);
-            first = 0;
-            if (from == min && i - 1 == max - 1) len += sprintf(buf, "*");
-            else if (from == i - 1) len += sprintf(buf, "%d", from);
-            else len += sprintf(buf, "%d-%d", from, i - 1);
-            STRCATC(dest, buf, 0);
-            from = -1;
+    int len = 0, first = 1, i, fs = -1, ls = -1, d = -1, ns = 0, from, dt;
+    for (i = min; i < max; i++) {
+        if (cron_get_bit(bits, i + offset)) {
+            ns++;
+            if (fs == -1) fs = i;
+            else {
+                dt = i - ls;
+                if (d == -1) d = dt;
+                else if (d != dt) { d = -1; break; }
+            }
+            ls = i;
         }
     }
+    if (ns == max - min) len += sprintf(buf, "*");
+    else if (d < 2 || ns < 3) {
+        from = -1;
+        for (i = min; i <= max; i++) {
+            if ((i < max) ? cron_get_bit(bits, i + offset) : 0) { if (from == -1) from = i; }
+            else if (from != -1) {
+                if (!first) STRCATC(dest, ",", 1);
+                first = 0;
+                len += from == i-1 ? sprintf(buf, "%d", from) : sprintf(buf, "%d-%d", from, i-1);
+                from = -1;
+                STRCATC(dest, buf, 0);
+            }
+        }
+        return len;
+    } else if (fs == min && ls == max - 1 && min % d == 0 || fs == 0) len += sprintf(buf, "*/%d", d);
+    else if (((max - fs - 1) / d) + 1 != ns) len += sprintf(buf, "%d-%d/%d", fs, ls, d);
+    else len += sprintf(buf, "%d/%d", fs, d);
+    STRCATC(dest, buf, 0);
     return len;
 }
 
diff --git a/ccronexpr_test.c b/ccronexpr_test.c
index 4801c7b..641c05d 100644
--- a/ccronexpr_test.c
+++ b/ccronexpr_test.c
@@ -843,6 +843,9 @@ void test_parse() {
     check_expr_valid("0 0 12 ? 1,3,5,7,9,11 *"); /* Every odd month at noon. */
     check_expr_valid("0 0 0 ? 2,4,6,8,10,12 *"); /* Every even month at midnight. */
     check_expr_valid("0 0 12 * * ? 2027"); /* Every day at noon in the year 2027. */
+ 
+    check_expr_valid("0 6,9,12 0 * 4,6,8 *");
+    check_expr_valid("0 6,9,12,16,20,24 0 * 2,4,6,8,9,10 *");
 }
 
 void test_bits() {