meetup (C)

c/meetup/src/meetup.c

@@ -0,0 +1,106 @@
+#include "meetup.h"
+#include <time.h>
+#include <stdlib.h>
+
+/* The explanation tells about 'fifth', not included in tests.
+ * I will manage this, returning "-1" if it does not exist.
+ */
+
+/* convert the 2/3 first chars of string to big endian integer */
+#define S2BE(a, b) ((a<<8)+b)
+#define S3BE(a, b, c) ((a<<16)+(b<<8)+c)
+
+#define TEENTH 42
+#define LAST   21
+
+static int str2day(const char *d)
+{
+    switch (S2BE(*d, *(d+1))) {
+        case S2BE('M', 'o'): return 1;
+        case S2BE('T', 'u'): return 2;
+        case S2BE('W', 'e'): return 3;
+        case S2BE('T', 'h'): return 4;
+        case S2BE('F', 'r'): return 5;
+        case S2BE('S', 'a'): return 6;
+        case S2BE('S', 'u'): return 0;
+    }
+    return -1;
+}
+
+static int str2nth(const char *d)
+{
+    switch (S3BE(*d, *(d+1), *(d+2))) {
+        case S3BE('f', 'i', 'r'): return 0;
+        case S3BE('s', 'e', 'c'): return 1;
+        case S3BE('t', 'h', 'i'): return 2;
+        case S3BE('f', 'o', 'u'): return 3;
+        case S3BE('f', 'i', 'f'): return 4;
+        case S3BE('l', 'a', 's'): return LAST;
+        case S3BE('t', 'e', 'e'): return TEENTH;
+    }
+    return -1;
+}
+
+static int m_1st(unsigned y, unsigned m)
+{
+    struct tm time = {
+        .tm_year=y-1900,
+        .tm_mon=m-1,
+        .tm_mday=1
+    };
+    mktime (&time);
+    return time.tm_wday;
+}
+
+static int m_ndays(unsigned y, unsigned m)
+{
+    static int days[]={31, 42, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
+    return m!=2 ? days[m-1]:
+        (!(y % 4) && (y % 100 || !(y % 400)))? 29: 28;
+
+}
+
+int meetup_day_of_month(unsigned int yy, unsigned int mm, const char *sweek,
+                        const char *sday)
+{
+
+    int nth, ndays, wanted, res=-1;
+
+    ndays=m_ndays(yy, mm);
+    if ((nth=str2nth(sweek))<0 || (wanted=str2day(sday))<0)
+        return -1;
+    if ((res=wanted-m_1st(yy, mm)+1) <= 0)
+        res+=7;
+
+    if (nth<5) {
+        if ((res+=7*nth)>ndays)
+            res=-1;
+    } else if (nth==TEENTH) {
+        if ((res+=7)<13)
+            res+=7;
+    } else {                                      /* last */
+        if ((res+=7*4)>ndays)
+            res-=7;
+    }
+
+    return res;
+}
+
+/* See GNUmakefile below for explanation
+ * https://github.com/braoult/exercism/blob/master/c/templates/GNUmakefile
+ */
+#ifdef UNIT_TEST
+int main(int ac, char **av)
+{
+    int arg=1;
+    unsigned y, m;
+
+    for (; arg<ac-3; arg+=4) {
+        y=atoi(av[arg]);
+        m=atoi(av[arg+1]);
+        printf("meetup(%d, %d, %s, %s)=%d\n",
+               y, m, av[arg+2], av[arg+3],
+               meetup_day_of_month(y, m, av[arg+2], av[arg+3]));
+    }
+}
+#endif

c/meetup/src/meetup.h

@@ -0,0 +1,19 @@
+#ifndef MEETUP_H
+#define MEETUP_H
+
+int meetup_day_of_month(unsigned int year, unsigned int month, const char *week,
+                        const char *day_of_week);
+
+/* See GNUmakefile below for explanation
+ * https://github.com/braoult/exercism/blob/master/c/templates/GNUmakefile
+ */
+#if defined UNIT_TEST || defined DEBUG
+#include <stdio.h>
+#include <stdlib.h>
+#endif
+#ifdef  TESTALL
+#undef  TEST_IGNORE
+#define TEST_IGNORE() {}
+#endif
+
+#endif