From e6d24a68ba902f96c317f0329de4d61032177e6b Mon Sep 17 00:00:00 2001
From: Cliff Click <cliffc@acm.org>
Date: Mon, 10 Aug 2026 11:11:18 -0700
Subject: Chapter 31: Software Drawing, Time, and Graphical Games

Co-authored-by: Hsiang-Ying Fu <66062782+fuhsnn@users.noreply.github.com>
Co-authored-by: fuhsnn <66062782+fuhsnn@users.noreply.github.com>
Co-authored-by: Symious <14933944+symious@users.noreply.github.com>
Co-authored-by: Jun Kawasaki <jun784@gmail.com>
Co-authored-by: Claude Opus 5 <noreply@anthropic.com>
---
 src/main/c/simple_time.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 61 insertions(+)
 create mode 100644 src/main/c/simple_time.c

(limited to 'src/main/c/simple_time.c')

diff --git a/src/main/c/simple_time.c b/src/main/c/simple_time.c
new file mode 100644
index 00000000..2e579922
--- /dev/null
+++ b/src/main/c/simple_time.c
@@ -0,0 +1,61 @@
+#define _POSIX_C_SOURCE 200809L
+#include <time.h>
+#include <stdint.h>
+#include <errno.h>
+
+// Fixed-width bridge; no native struct layout or retained Simple pointers.
+static int64_t clock_value(clockid_t clock, int64_t scale) {
+    struct timespec t;
+    if (clock_gettime(clock,&t)) return -1;
+    if (t.tv_sec>INT64_MAX/scale || t.tv_sec<INT64_MIN/scale) {
+        errno=EOVERFLOW; return -1;
+    }
+    int64_t base=(int64_t)t.tv_sec*scale;
+    int64_t fraction=t.tv_nsec/(1000000000/scale);
+    if (base>INT64_MAX-fraction) { errno=EOVERFLOW; return -1; }
+    return base+fraction;
+}
+int64_t simple_time_now(void) { return clock_value(CLOCK_REALTIME,1000); }
+int64_t simple_time_mono(void) { return clock_value(CLOCK_MONOTONIC,1000); }
+int64_t simple_time_nano(void) { return clock_value(CLOCK_MONOTONIC,1000000000); }
+int32_t simple_time_sleep(int64_t ms, int32_t absolute) {
+    if (ms<0) { errno=EINVAL; return -1; }
+    struct timespec t={ms/1000,(ms%1000)*1000000};
+    int result;
+    if (!absolute) {
+        // Retry the remaining duration after signals; no busy waiting.
+        do { result=nanosleep(&t,&t); } while (result && errno==EINTR);
+        return result;
+    }
+    do { result=clock_nanosleep(CLOCK_MONOTONIC,TIMER_ABSTIME,&t,NULL); } while (result==EINTR);
+    if (result) { errno=result; return -1; }
+    return 0;
+}
+static int leap(int y) { return y%4==0 && (y%100!=0 || y%400==0); }
+static int local_fields(int64_t ms, struct tm *local, struct tm *utc) {
+    tzset();
+    int64_t sec=ms/1000;
+    if (ms%1000<0) --sec;
+    time_t t=(time_t)sec;
+    if ((int64_t)t!=sec || !localtime_r(&t,local) || !gmtime_r(&t,utc)) return -1;
+    if (local->tm_year < -1899 || local->tm_year > 8099) { errno=EOVERFLOW; return -1; }
+    return 0;
+}
+int32_t simple_time_local(int64_t ms, int64_t *out) {
+    struct tm t,u;
+    if (local_fields(ms,&t,&u)) return -1;
+    int days=t.tm_yday-u.tm_yday;
+    if (t.tm_year>u.tm_year) days+=365+leap(u.tm_year+1900);
+    if (t.tm_year<u.tm_year) days-=365+leap(t.tm_year+1900);
+    int offset=days*86400+(t.tm_hour-u.tm_hour)*3600+(t.tm_min-u.tm_min)*60+t.tm_sec-u.tm_sec;
+    out[0]=t.tm_year+1900; out[1]=t.tm_mon+1; out[2]=t.tm_mday;
+    out[3]=t.tm_hour; out[4]=t.tm_min; out[5]=t.tm_sec;
+    out[6]=(ms%1000+1000)%1000; out[7]=t.tm_wday;
+    out[8]=offset; out[9]=t.tm_isdst>0;
+    return 0;
+}
+int32_t simple_time_zone(int64_t ms, char *out, uint32_t capacity) {
+    struct tm t,u;
+    if (!capacity || local_fields(ms,&t,&u)) return -1;
+    return (int32_t)strftime(out,capacity,"%Z",&t);
+}
-- 
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