ISO week calculation.

[pdclib] / functions / _PDCLIB / _PDCLIB_is_leap.c

diff --git a/functions/_PDCLIB/_PDCLIB_is_leap.c b/functions/_PDCLIB/_PDCLIB_is_leap.c
new file mode 100644 (file)
index 0000000..80ea70b
--- /dev/null
+++ b/functions/_PDCLIB/_PDCLIB_is_leap.c
@@ -0,0 +1,39 @@
+/* _PDCLIB_is_leap( int )
+
+   This file is part of the Public Domain C Library (PDCLib).
+   Permission is granted to use, modify, and / or redistribute at will.
+*/
+
+#include "_PDCLIB_int.h"
+
+#ifndef REGTEST
+
+int _PDCLIB_is_leap( int year_offset )
+{
+    /* year given as offset from 1900, matching tm.tm_year in <time.h> */
+    long long year = year_offset + 1900ll;
+    return ( ( year % 4 ) == 0 && ( ( year % 25 ) != 0 || ( year % 400 ) == 0 ) );
+}
+
+#endif
+
+#ifdef TEST
+
+#include "_PDCLIB_test.h"
+
+int main( void )
+{
+#ifndef REGTEST
+    /* 1901 not leap */
+    TESTCASE( ! _PDCLIB_is_leap( 1 ) );
+    /* 1904 leap */
+    TESTCASE( _PDCLIB_is_leap( 4 ) );
+    /* 1900 not leap */
+    TESTCASE( ! _PDCLIB_is_leap( 0 ) );
+    /* 2000 leap */
+    TESTCASE( _PDCLIB_is_leap( 100 ) );
+#endif
+    return TEST_RESULTS;
+}
+
+#endif