import and use timegm from musl

It's ridiculous this function is not in the standards.

COPYING

@@ -6,7 +6,7 @@ has waived all copyright and related or neighboring rights to this work.
 http://creativecommons.org/publicdomain/zero/1.0/
 
 
-The files mystrverscmp.c and mymemmem.c
+The files mystrverscmp.c and mymemmem.c and mytimegm.c
 are MIT-licensed and were written by Rich Felker.
 
 mpick.c is largely based on code by Christian Neukirchen

Makefile

@@ -10,24 +10,24 @@ SCRIPT = mcolor mcom mless mquote
 
 all: $(ALL)
 
-maddr: maddr.o blaze822.o seq.o rfc2047.o mymemmem.o
-magrep: magrep.o blaze822.o seq.o rfc2045.o rfc2047.o mymemmem.o
+maddr: maddr.o blaze822.o seq.o rfc2047.o mymemmem.o mytimegm.o
+magrep: magrep.o blaze822.o seq.o rfc2045.o rfc2047.o mymemmem.o mytimegm.o
 mdate: mdate.o
-mdeliver: mdeliver.o blaze822.o mymemmem.o
+mdeliver: mdeliver.o blaze822.o mymemmem.o mytimegm.o
 mdirs: mdirs.o
-mflag: mflag.o blaze822.o seq.o mymemmem.o
-mgenmid: mgenmid.o blaze822.o seq.o mymemmem.o
-mhdr: mhdr.o blaze822.o seq.o rfc2047.o mymemmem.o
+mflag: mflag.o blaze822.o seq.o mymemmem.o mytimegm.o
+mgenmid: mgenmid.o blaze822.o seq.o mymemmem.o mytimegm.o
+mhdr: mhdr.o blaze822.o seq.o rfc2047.o mymemmem.o mytimegm.o
 minc: minc.o
 mlist: mlist.o
 mmime: mmime.o
-mpick: mpick.o blaze822.o seq.o rfc2047.c mymemmem.o
-mscan: mscan.o blaze822.o seq.o rfc2047.o mymemmem.o
-msed: msed.o blaze822.o seq.o mymemmem.o
+mpick: mpick.o blaze822.o seq.o rfc2047.c mymemmem.o mytimegm.o
+mscan: mscan.o blaze822.o seq.o rfc2047.o mymemmem.o mytimegm.o
+msed: msed.o blaze822.o seq.o mymemmem.o mytimegm.o
 mseq: mseq.o seq.o
-mshow: mshow.o blaze822.o seq.o rfc2045.o rfc2047.c mymemmem.o filter.o
-msort: msort.o blaze822.o seq.o mystrverscmp.o mymemmem.o
-mthread: mthread.o blaze822.o seq.o mymemmem.o
+mshow: mshow.o blaze822.o seq.o rfc2045.o rfc2047.c mymemmem.o filter.o mytimegm.o
+msort: msort.o blaze822.o seq.o mystrverscmp.o mymemmem.o mytimegm.o
+mthread: mthread.o blaze822.o seq.o mymemmem.o mytimegm.o
 
 README: man/mblaze.7
 	mandoc -Tutf8 $< | col -bx >$@

blaze822.c

@@ -121,7 +121,7 @@ blaze822_date(char *s) {
 
 	tm.tm_isdst = -1;
 
-	time_t r = mktime(&tm);
+	time_t r = tm_to_secs(&tm);
 	return r;
 
 fail:

blaze822.h

@@ -1,6 +1,8 @@
-#include <stdint.h>
 #include <sys/types.h>
 
+#include <stdint.h>
+#include <time.h>
+
 struct message;
 
 // blaze822.c
@@ -71,3 +73,7 @@ char *blaze822_home_file(char *basename);
 // filter.c
 
 int filter(char *input, size_t inlen, char *cmd, char **outputo, size_t *outleno);
+
+// mygmtime.c
+
+time_t tm_to_secs(const struct tm *tm);

mytimegm.c

@@ -0,0 +1,86 @@
+#include <time.h>
+
+// from musl@1cc81f5cb, slightly tweaked
+
+static long long
+__year_to_secs(long long year, int *is_leap)
+{
+        if (year-2ULL <= 136) {
+                int y = year;
+                int leaps = (y-68)>>2;
+                if (!((y-68)&3)) {
+                        leaps--;
+                        if (is_leap) *is_leap = 1;
+                } else if (is_leap) *is_leap = 0;
+                return 31536000*(y-70) + 86400*leaps;
+        }
+
+        int cycles, centuries, leaps, rem;
+
+        cycles = (year-100) / 400;
+        rem = (year-100) % 400;
+        if (rem < 0) {
+                cycles--;
+                rem += 400;
+        }
+        if (!rem) {
+                *is_leap = 1;
+                centuries = 0;
+                leaps = 0;
+        } else {
+                if (rem >= 200) {
+                        if (rem >= 300) centuries = 3, rem -= 300;
+                        else centuries = 2, rem -= 200;
+                } else {
+                        if (rem >= 100) centuries = 1, rem -= 100;
+                        else centuries = 0;
+                }
+                if (!rem) {
+                        *is_leap = 0;
+                        leaps = 0;
+                } else {
+                        leaps = rem / 4U;
+                        rem %= 4U;
+                        *is_leap = !rem;
+                }
+        }
+
+        leaps += 97*cycles + 24*centuries - *is_leap;
+
+        return (year-100) * 31536000LL + leaps * 86400LL + 946684800 + 86400;
+}
+
+static int
+__month_to_secs(int month, int is_leap)
+{
+        static const int secs_through_month[] = {
+                0, 31*86400, 59*86400, 90*86400,
+                120*86400, 151*86400, 181*86400, 212*86400,
+                243*86400, 273*86400, 304*86400, 334*86400 };
+        int t = secs_through_month[month];
+        if (is_leap && month >= 2) t+=86400;
+        return t;
+}
+
+time_t tm_to_secs(const struct tm *tm)
+{
+        int is_leap;
+        long long year = tm->tm_year;
+        int month = tm->tm_mon;
+        if (month >= 12 || month < 0) {
+                int adj = month / 12;
+                month %= 12;
+                if (month < 0) {
+                        adj--;
+                        month += 12;
+                }
+                year += adj;
+        }
+        long long t = __year_to_secs(year, &is_leap);
+        t += __month_to_secs(month, is_leap);
+        t += 86400LL * (tm->tm_mday-1);
+        t += 3600LL * tm->tm_hour;
+        t += 60LL * tm->tm_min;
+        t += tm->tm_sec;
+        return t;
+}