Fix Schism Tracker version date calculation.

Fixes several issues with the calculation of Schism Tracker dates.
Schism Tracker date calculation is now handled in a utility function.

* The date calculation was using a UTC epoch time but calculating
  the version date with localtime_r.
* The UTC epoch time was wrong (2009-10-01 instead of 2009-10-31).
* The S3M loader was not calculating Schism Tracker dates at all.
* Added detection for extended Schism Tracker dates (>2020-10-28)
  to both the S3M and IT loaders.

Additionally, the libxmp dependency on localtime_r has been entirely
removed in favor of an inline algorithm provided by Saga Musix.

configure.ac

@@ -150,7 +150,7 @@ darwin*)
   LIBS="${old_LIBS}"
   ;;
 esac
-AC_CHECK_FUNCS(popen mkstemp fnmatch umask localtime_r round powf)
+AC_CHECK_FUNCS(popen mkstemp fnmatch umask round powf)
 
 AC_CONFIG_FILES([Makefile])
 AC_CONFIG_FILES([libxmp.pc])

lite/configure.ac

@@ -149,7 +149,7 @@ darwin*)
   LIBS="${old_LIBS}"
   ;;
 esac
-AC_CHECK_FUNCS(localtime_r round powf)
+AC_CHECK_FUNCS(round powf)
 
 AC_CONFIG_FILES([Makefile])
 AC_CONFIG_FILES([libxmp-lite.pc])

src/loaders/common.c

@@ -364,3 +364,54 @@ void libxmp_set_type(struct module_data *m, const char *fmt, ...)
 	vsnprintf(m->mod.type, XMP_NAME_SIZE, fmt, ap);
 	va_end(ap);
 }
+
+static int schism_tracker_date(int year, int month, int day)
+{
+	int mm = (month + 9) % 12;
+	int yy = year - mm / 10;
+
+	yy = yy * 365 + (yy / 4) - (yy / 100) + (yy / 400);
+	mm = (mm * 306 + 5) / 10;
+
+	return yy + mm + (day - 1);
+}
+
+/* Generate a Schism Tracker version string.
+ * Schism Tracker versions are stored as follows:
+ *
+ * s_ver <= 0x50:		0.s_ver
+ * s_ver > 0x50, < 0xfff:	days from epoch=(s_ver - 0x50)
+ * s_ver = 0xfff:		days from epoch=l_ver
+ */
+void libxmp_schism_tracker_string(char *buf, size_t size, int s_ver, int l_ver)
+{
+	if (s_ver >= 0x50) {
+		/* time_t epoch_sec = 1256947200; */
+		int t = schism_tracker_date(2009, 10, 31);
+		int year, month, day, dayofyear;
+
+		if (s_ver == 0xfff) {
+			t += l_ver;
+		} else
+			t += s_ver - 0x50;
+
+		/* Date algorithm reimplemented from OpenMPT.
+		 */
+		year = (int)(((int64)t * 10000L + 14780) / 3652425);
+		dayofyear = t - (365 * year + (year / 4) - (year / 100) + (year / 400));
+		if (dayofyear < 0) {
+			year--;
+			dayofyear = t - (365 * year + (year / 4) - (year / 100) + (year / 400));
+		}
+		month = (100 * dayofyear + 52) / 3060;
+		day = dayofyear - (month * 306 + 5) / 10 + 1;
+
+		year += (month + 2) / 12;
+		month = (month + 2) % 12 + 1;
+
+		snprintf(buf, size, "Schism Tracker %04d-%02d-%02d",
+			year, month, day);
+	} else {
+		snprintf(buf, size, "Schism Tracker 0.%x", s_ver);
+	}
+}

src/loaders/it_load.c

@@ -22,7 +22,6 @@
 
 #ifndef LIBXMP_CORE_DISABLE_IT
 
-#include <time.h>
 #include "loader.h"
 #include "it.h"
 #include "period.h"
@@ -41,23 +40,6 @@ const struct format_loader libxmp_loader_it = {
 	it_load
 };
 
-#ifndef LIBXMP_CORE_PLAYER /* */
-#if defined(__WATCOMC__)
-#undef localtime_r
-#define localtime_r _localtime
-
-#elif !defined(HAVE_LOCALTIME_R) || defined(_WIN32)
-#undef localtime_r
-#define localtime_r libxmp_localtime_r
-static struct tm *libxmp_localtime_r(const time_t * timep, struct tm *result)
-{
-	/* Note: Win32 localtime() is thread-safe */
-	memcpy(result, localtime(timep), sizeof(struct tm));
-	return result;
-}
-#endif
-#endif /* ! LIBXMP_CORE_PLAYER */
-
 static int it_test(HIO_HANDLE * f, char *t, const int start)
 {
 	if (hio_read32b(f) != MAGIC_IMPM)
@@ -373,25 +355,10 @@ static void identify_tracker(struct module_data *m, struct it_file_header *ifh)
 		break;
 	default:
 		switch (ifh->cwt >> 12) {
-		case 0x1:{
-			uint16 cwtv = ifh->cwt & 0x0fff;
-			struct tm version;
-			time_t version_sec;
-
-			if (cwtv > 0x50) {
-				version_sec = ((cwtv - 0x050) * 86400) + 1254355200;
-				if (localtime_r(&version_sec, &version)) {
-					snprintf(tracker_name, 40,
-						 "Schism Tracker %04d-%02d-%02d",
-						 version.tm_year + 1900,
-						 version.tm_mon + 1,
-						 version.tm_mday);
-				}
-			} else {
-				snprintf(tracker_name, 40,
-					 "Schism Tracker 0.%x", cwtv);
-			}
-			break; }
+		case 0x1:
+			libxmp_schism_tracker_string(tracker_name, 40,
+				(ifh->cwt & 0x0fff), ifh->rsvd);
+			break;
 		case 0x5:
 			snprintf(tracker_name, 40, "OpenMPT %d.%02x",
 				 (ifh->cwt & 0x0f00) >> 8, ifh->cwt & 0xff);

src/loaders/loader.h

@@ -47,6 +47,7 @@ void	libxmp_get_instrument_path	(struct module_data *, char *, int);
 void	libxmp_set_type			(struct module_data *, const char *, ...);
 int	libxmp_load_sample		(struct module_data *, HIO_HANDLE *, int,
 					 struct xmp_sample *, const void *);
+void	libxmp_schism_tracker_string	(char *, size_t, int, int);
 
 extern uint8		libxmp_ord_xlat[];
 extern const int	libxmp_arch_vol_table[];

src/loaders/s3m_load.c

@@ -271,7 +271,7 @@ static int s3m_load(struct module_data *m, HIO_HANDLE * f, const int start)
 	sfh.mv = buf[51];			/* Master volume */
 	sfh.uc = buf[52];			/* Ultra click removal */
 	sfh.dp = buf[53];			/* Default pan positions if 0xfc */
-	/* 54-61 reserved */
+	memcpy(sfh.rsvd2, buf + 54, 8);		/* Reserved */
 	sfh.special = readmem16l(buf + 62);	/* Ptr to special custom data */
 	memcpy(sfh.chset, buf + 64, 32);	/* Channel settings */
 
@@ -418,9 +418,8 @@ static int s3m_load(struct module_data *m, HIO_HANDLE * f, const int start)
 		break;
 	case 4:
 		if (sfh.version != 0x4100) {
-			snprintf(tracker_name, 40, "Schism Tracker %d.%02x",
-				 (sfh.version & 0x0f00) >> 8,
-				 sfh.version & 0xff);
+			libxmp_schism_tracker_string(tracker_name, 40,
+				(sfh.version & 0x0fff), sfh.rsvd2[0] | (sfh.rsvd2[1] << 8));
 			break;
 		}
 		/* fall through */