Add timegm reimplementation.

Makefile

@@ -12,21 +12,24 @@ LIBRARIES = check glib-2.0
 all: test example
 	@echo "+++ All good."""
 
-test: tests/test-parser
+test: tests/test-parser tests/test-timegm
 	@echo "+++ Running parser test suite."
 	tests/test-parser
+	@echo "+++ Running at-timegm test suite."
+	tests/test-timegm
 
 clean:
-	$(RM) src/example-at src/example-sim800 tests/test-parser
+	$(RM) src/example-at src/example-sim800 tests/test-parser tests/test-timegm
 	$(RM) src/*.o src/modem/*.o tests/*.o
 
 PARSER = include/attentive/parser.h
 AT = include/attentive/at.h include/attentive/at-unix.h $(PARSER)
-CELLULAR = include/attentive/cellular.h $(AT)
+CELLULAR = include/attentive/cellular.h include/attentive/at-timegm.h $(AT)
 MODEM = src/modem/common.h $(CELLULAR)
 
 src/parser.o: src/parser.c $(PARSER)
 src/at-unix.o: src/at-unix.c $(AT)
+src/at-timegm.o: src/at-timegm.c
 src/cellular.o: src/cellular.c $(CELLULAR)
 src/modem/common.o: src/modem/common.c $(MODEM)
 src/modem/generic.o: src/modem/generic.c $(MODEM)
@@ -37,8 +40,9 @@ src/example-at.o: src/example-at.c $(AT)
 src/example-sim800.o: src/example-sim800.c $(CELLULAR)
 
 tests/test-parser: tests/test-parser.o src/parser.o
+tests/test-timegm: tests/test-timegm.o src/at-timegm.o
 
-src/example-at: src/example-at.o src/parser.o src/at-unix.o
-src/example-sim800: src/example-sim800.o src/modem/sim800.o src/modem/common.o src/cellular.o src/at-unix.o src/parser.o
+src/example-at: src/example-at.o src/parser.o src/at-unix.o src/at-timegm.o
+src/example-sim800: src/example-sim800.o src/modem/sim800.o src/modem/common.o src/cellular.o src/at-unix.o src/at-timegm.o src/parser.o
 
 .PHONY: all test clean

include/attentive/at-timegm.h

@@ -0,0 +1,19 @@
+/*
+ * Copyright © 2025 Zyax AB
+ * This program is free software. It comes without any warranty, to the extent
+ * permitted by applicable law. You can redistribute it and/or modify it under
+ * the terms of the Do What The Fuck You Want To Public License, Version 2, as
+ * published by Sam Hocevar. See the COPYING file for more details.
+ */
+
+#ifndef ATTENTIVE_AT_UNIX_H
+#define ATTENTIVE_AT_UNIX_H
+
+#include <time.h>
+#include <stdint.h>
+
+time_t at_timegm(const struct tm *tm);
+
+#endif
+
+/* vim: set ts=4 sw=4 et: */

src/at-timegm.c

@@ -0,0 +1,62 @@
+#include <attentive/at-timegm.h>
+
+static int is_leap_year(int year)
+{
+    return (year % 4 == 0 && (year % 100 != 0 || year % 400 == 0));
+}
+
+static int days_in_month(int year, int month)
+{
+    static const int days[12] = { 31,28,31,30,31,30,31,31,30,31,30,31 };
+    if (month == 1 && is_leap_year(year)) {
+        return 29;
+    }
+    return days[month];
+}
+
+time_t at_timegm(const struct tm *tm)
+{
+    int year = tm->tm_year + 1900;
+    int month = tm->tm_mon;
+    int day = tm->tm_mday;
+    int hour = tm->tm_hour;
+    int minute = tm->tm_min;
+    int second = tm->tm_sec;
+
+    // Normalize month and year
+    if (month > 11) {
+        year += month / 12;
+        month %= 12;
+    } else if (month < 0) {
+        int years_diff = (11 - month) / 12;
+        year -= years_diff;
+        month += 12 * years_diff;
+    }
+
+    // Days since Unix epoch
+    int64_t days = 0;
+
+    // Years to days
+    for (int y = 1970; y < year; ++y) {
+        days += is_leap_year(y) ? 366 : 365;
+    }
+    for (int y = year; y < 1970; ++y) {
+        days -= is_leap_year(y) ? 366 : 365;
+    }
+
+    // Months to days
+    for (int m = 0; m < month; ++m) {
+        days += days_in_month(year, m);
+    }
+
+    // Days
+    days += (day - 1);
+
+    // Total seconds
+    int64_t total_seconds = days * 86400
+                           + hour * 3600
+                           + minute * 60
+                           + second;
+
+    return (time_t)total_seconds;
+}

src/modem/common.c

@@ -7,6 +7,7 @@
  */
 
 #include <attentive/cellular.h>
+#include <attentive/at-timegm.h>
 
 #include <stdio.h>
 #include <string.h>
@@ -135,7 +136,7 @@ int cellular_op_clock_gettime(struct cellular *modem, struct timespec *ts)
     /* Adjust values and perform conversion. */
     tm.tm_year += 2000 - 1900;
     tm.tm_mon -= 1;
-    time_t unix_time = timegm(&tm);
+    time_t unix_time = at_timegm(&tm);
     if (unix_time == -1) {
         errno = EINVAL;
         return -1;

src/modem/telit2.c

@@ -7,6 +7,7 @@
  */
 
 #include <attentive/cellular.h>
+#include <attentive/at-timegm.h>
 
 #include <stdio.h>
 #include <string.h>
@@ -159,7 +160,7 @@ static int telit2_op_clock_gettime(struct cellular *modem, struct timespec *ts)
     /* Adjust values and perform conversion. */
     tm.tm_year += 2000 - 1900;
     tm.tm_mon -= 1;
-    time_t unix_time = timegm(&tm);
+    time_t unix_time = at_timegm(&tm);
     if (unix_time == -1) {
         errno = EINVAL;
         return -1;

tests/.gitignore

@@ -1 +1,3 @@
 test-parser
+test-timegm
+

tests/test-timegm.c

@@ -0,0 +1,64 @@
+/*
+ * Copyright © 2015 Zyax AB
+ * This program is free software. It comes without any warranty, to the extent
+ * permitted by applicable law. You can redistribute it and/or modify it under
+ * the terms of the Do What The Fuck You Want To Public License, Version 2, as
+ * published by Sam Hocevar. See the COPYING file for more details.
+ */
+
+ #include <math.h>
+ #include <stdio.h>
+ #include <stdlib.h>
+ #include <string.h>
+
+ #include <check.h>
+ #include <glib.h>
+
+ #include <attentive/at-timegm.h>
+
+
+ START_TEST(test_timegm)
+ {
+     printf(":: test_timegm\n");
+
+     struct tm tmg = {
+        .tm_sec = 7,
+        .tm_min = 14,
+        .tm_hour = 3,
+        .tm_mday = 19,
+        .tm_mon = 0,
+        .tm_year = 138,
+        .tm_wday = 2,
+        .tm_yday = 18,
+        .tm_isdst = 0
+    };
+
+    time_t t = at_timegm(&tmg);
+    ck_assert_int_eq(t, 0x7fffffff);
+ }
+ END_TEST
+
+ Suite *attentive_suite(void)
+ {
+     Suite *s = suite_create("attentive");
+     TCase *tc;
+
+     tc = tcase_create("timegm");
+     tcase_add_test(tc, test_timegm);
+     suite_add_tcase(s, tc);
+
+     return s;
+ }
+
+ int main()
+ {
+     int number_failed;
+     Suite *s = attentive_suite();
+     SRunner *sr = srunner_create(s);
+     srunner_run_all(sr, CK_NORMAL);
+     number_failed = srunner_ntests_failed(sr);
+     srunner_free(sr);
+     return (number_failed == 0) ? EXIT_SUCCESS : EXIT_FAILURE;
+ }
+
+ /* vim: set ts=4 sw=4 et: */