From 4abab5ad6c8465a7528ccdd5f49367da05f78bbd Mon Sep 17 00:00:00 2001
From: Vladimir Azarov <avm@intermediate-node.net>
Date: Tue, 1 Oct 2024 15:47:05 +0200
Subject: Initial version

---
 src/time/__year_to_secs.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)
 create mode 100644 src/time/__year_to_secs.c

(limited to 'src/time/__year_to_secs.c')

diff --git a/src/time/__year_to_secs.c b/src/time/__year_to_secs.c
new file mode 100644
index 0000000..b42f5a6
--- /dev/null
+++ b/src/time/__year_to_secs.c
@@ -0,0 +1,47 @@
+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, dummy;
+
+	if (!is_leap) is_leap = &dummy;
+	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;
+}
-- 
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