diff options
| -rw-r--r-- | src/gsm/gsm0411_utils.c | 40 |
1 files changed, 32 insertions, 8 deletions
diff --git a/src/gsm/gsm0411_utils.c b/src/gsm/gsm0411_utils.c index 71973a95..0dd5ff84 100644 --- a/src/gsm/gsm0411_utils.c +++ b/src/gsm/gsm0411_utils.c @@ -72,14 +72,43 @@ uint8_t gsm411_unbcdify(uint8_t value) return ret; } +/* Get the local timezone offset from GMT of the unix time provided. + * For this the unix time is converted to a struct tm representation once + * as localtime and once as UTC. As there are no portable functions to + * calculate the differerence of two struct tm convert them both back to + * a unix timestamp and calculate the difference. */ +static time_t time_gmtoff(time_t time) +{ + struct tm tm_local, tm_utc; + time_t ts_local, ts_utc; + + tzset(); + localtime_r(&time, &tm_local); + gmtime_r(&time, &tm_utc); + + /* tm_local is already in local time with DST offset included. For the + * conversion back reset DST flag to 0. */ + tm_local.tm_isdst = 0; + tm_utc.tm_isdst = 0; + ts_local = mktime(&tm_local); + ts_utc = mktime(&tm_utc); + + return ts_local - ts_utc; +} + /* Generate 03.40 TP-SCTS */ void gsm340_gen_scts(uint8_t *scts, time_t time) { struct tm tm; + int gmt_offset; + /* The reentrant function require tzset() to be called */ tzset(); localtime_r(&time, &tm); + /* Get the gmt offset */ + gmt_offset = time_gmtoff(time); + *scts++ = gsm411_bcdify(tm.tm_year % 100); *scts++ = gsm411_bcdify(tm.tm_mon + 1); *scts++ = gsm411_bcdify(tm.tm_mday); @@ -87,15 +116,10 @@ void gsm340_gen_scts(uint8_t *scts, time_t time) *scts++ = gsm411_bcdify(tm.tm_min); *scts++ = gsm411_bcdify(tm.tm_sec); -#ifdef HAVE_TM_GMTOFF_IN_TM - if (tm.tm_gmtoff >= 0) - *scts++ = gsm411_bcdify(tm.tm_gmtoff/(60*15)); + if (gmt_offset >= 0) + *scts++ = gsm411_bcdify(gmt_offset/(60*15)); else - *scts++ = gsm411_bcdify(-tm.tm_gmtoff/(60*15)) | 0x08; -#else -#warning find a portable way to obtain timezone offset - *scts++ = 0; -#endif + *scts++ = gsm411_bcdify(-gmt_offset/(60*15)) | 0x08; } /* Decode 03.40 TP-SCTS (into utc/gmt timestamp) */ |