time.h: time, difftime calls

inc/locale.h

@@ -4,6 +4,14 @@
 #define _COL_IGNORE_SPACE  0x1
 #define _COL_IGNORE_SYMBOL 0x2
 
+// Locale categories
+#define LC_ALL          0
+#define LC_COLLATE      1
+#define LC_CTYPE        2
+#define LC_MONETARY     3
+#define LC_NUMERIC      4
+#define LC_TIME         5
+
 struct lconv {
 	// LC_NUMERIC
 	char *decimal_point;     // "."
@@ -33,13 +41,5 @@ struct lconv {
 	char int_n_sign_posn;    // CHAR_MAX
 };
 
-// Locale categories
-#define LC_ALL          0
-#define LC_COLLATE      1
-#define LC_CTYPE        2
-#define LC_MONETARY     3
-#define LC_NUMERIC      4
-#define LC_TIME         5
-
 char *setlocale(int category, const char *locale);
 struct lconv *localeconv(void);

inc/time.h

@@ -1,45 +1,51 @@
 #pragma once
-#include <stddef.h>
+
+#include <stdint.h>
 
 #if !defined(NULL)
 #define NULL ((void *)0)
 #endif
 
-// The number of clock ticks per second
-#define CLOCKS_PER_SEC  ((clock_t)1000)
-
 #define TIME_UTC 1
 
-typedef size_t clock_t;
-typedef size_t time_t;
+#define CLOCKS_PER_SEC  ((clock_t)1000000)
+
+typedef uint64_t clock_t;
+typedef uint64_t time_t;
 
 struct timespec {
-	time_t tv_sec;  // Seconds - >= 0
-	long   tv_nsec; // Nanoseconds - [0, 999999999]
+	time_t tv_sec;
+	long   tv_nsec;
 };
 
 struct tm {
-    int tm_sec;   // seconds after the minute - [0, 60] including leap second
-    int tm_min;   // minutes after the hour - [0, 59]
-    int tm_hour;  // hours since midnight - [0, 23]
-    int tm_mday;  // day of the month - [1, 31]
-    int tm_mon;   // months since January - [0, 11]
-    int tm_year;  // years since 1900
-    int tm_wday;  // days since Sunday - [0, 6]
-    int tm_yday;  // days since January 1 - [0, 365]
-    int tm_isdst; // daylight savings time flag
+    int tm_sec;
+    int tm_min;
+    int tm_hour;
+    int tm_mon;
+    int tm_mday; // Days passed within 1st of current month
+    int tm_year; // Years since year 1900
+    int tm_wday; // Days passed since sunday
+    int tm_yday; // Days passed since Jan 1
+    int tm_isdst;
 };
 
-clock_t clock(void);
-double difftime(time_t time1, time_t time0);
-time_t mktime(struct tm *timeptr);
-time_t time(time_t *timer);
+clock_t    clock       (void);
+time_t     time        (time_t *timer);
+time_t     mktime      (struct tm *timeptr);
+double     difftime    (time_t time1, time_t time0);
 int        timespec_get(struct timespec *ts, int base);
-char *asctime(const struct tm *timeptr);
-char *ctime(const time_t *timer);
-struct tm *gmtime(const time_t *timer);
-struct tm *localtime(const time_t *timer);
-size_t strftime(char * restrict s, size_t maxsize, const char * restrict format, const struct tm * restrict timeptr);
+char      *asctime     (const struct tm *timeptr);
+char      *ctime       (const time_t *timer);
+struct tm *gmtime      (const time_t *timer);
+struct tm *localtime   (const time_t *timer);
+
+size_t strftime(
+    char *restrict s,
+    size_t maxsize,
+    const char *restrict format,
+    const struct tm *restrict timeptr
+);
 
 #ifdef __STDC_WANT_LIB_EXT1__
 errno_t asctime_s(char *s, rsize_t maxsize, const struct tm *timeptr);

src/win/win_time.c

@@ -3,6 +3,15 @@
 #include <stdint.h>
 #include <win.h>
 
+#define TIME_TICKS_PER_SEC          1000
+#define FILE_TICKS_PER_SEC          10000000
+#define FILE_TICKS_UNTIL_UNIX_EPOCH 116444736000000000ULL
+
+#define NANOS_PER_SEC               1000000000
+#define NANOS_PER_FILE_TICK         (NANOS_PER_SEC / FILE_TICKS_PER_SEC)
+#define NANOS_PER_TIME_TICK         (NANOS_PER_SEC / TIME_TICKS_PER_SEC)
+
+
 // Store the time since we started running the process
 static uint64_t timer_freq;
 static uint64_t timer_start;
@@ -15,21 +24,17 @@ void _setup_timer(void) {
     timer_freq  = freq.QuadPart;
 }
 
-int timespec_get(struct timespec *ts, int base) {
-    if (base != TIME_UTC) return 0;
-
+static ULONGLONG win32_get_unix_nanos() {
     FILETIME ft;
     GetSystemTimeAsFileTime(&ft);
-
-    ULARGE_INTEGER s = {
+    ULARGE_INTEGER ft64 = {
         .LowPart  = ft.dwLowDateTime,
-        .HighPart = ft.dwHighDateTime
+        .HighPart = ft.dwHighDateTime,
     };
-
-    ULONGLONG t = s.QuadPart - 116444736000000000ULL;
-    ts->tv_sec = t / 10000000;
-    ts->tv_nsec = ((int) (t % 10000000)) * 100;
-    return base;
+    ULONGLONG fticks      = ft64.QuadPart;
+    ULONGLONG unix_fticks = fticks - FILE_TICKS_UNTIL_UNIX_EPOCH;
+    ULONGLONG unix_nanos  = unix_fticks * NANOS_PER_FILE_TICK;
+    return unix_nanos;
 }
 
 clock_t clock(void) {
@@ -37,17 +42,34 @@ clock_t clock(void) {
     if (!QueryPerformanceCounter(&curr)) {
         return -1;
     }
-
-    // time travel?
     if (curr.QuadPart < timer_start) {
         return -1;
     }
-
-    uint64_t time_from_start = curr.QuadPart - timer_start;
-
-    uint64_t scaled_millis = (time_from_start / timer_freq) * CLOCKS_PER_SEC;
-    // helps reduce error when doing integer division
-    scaled_millis += ((time_from_start % timer_freq) * CLOCKS_PER_SEC) / timer_freq;
-
-    return scaled_millis;
+    clock_t ticks = curr.QuadPart - timer_start;
+    // Basically millis / timer_freq * CLOCKS_PER_SEC but more precise
+    return ticks / timer_freq * CLOCKS_PER_SEC
+         + ticks % timer_freq * CLOCKS_PER_SEC / timer_freq;
+}
+
+time_t time(time_t *timer) {
+    ULONGLONG unix_nanos  = win32_get_unix_nanos();
+    time_t    timer_ticks = unix_nanos / NANOS_PER_TIME_TICK;
+    if(timer != NULL) {
+        *timer = timer_ticks;
+    }
+    return timer_ticks;
+}
+
+double difftime(time_t time1, time_t time0) {
+    double resolution = (double)TIME_TICKS_PER_SEC;
+    if(time1 >= time0) return  (double)(time1 - time0) / resolution;
+    else               return -(double)(time0 - time1) / resolution;
+}
+
+int timespec_get(struct timespec *ts, int base) {
+    if (base != TIME_UTC) return 0;
+    ULONGLONG unix_nanos = win32_get_unix_nanos();
+    ts->tv_sec  = unix_nanos / NANOS_PER_SEC;
+    ts->tv_nsec = unix_nanos;
+    return base;
 }

test/test_time.c

@@ -0,0 +1,10 @@
+
+#include <time.h>
+#include <stdio.h>
+
+int main() {
+    time_t t1 = time(NULL);
+    time_t t2 = time(NULL);
+    double s = difftime(t2, t1);
+    return 0;
+}