rail fence cipher (C)

c/rail-fence-cipher/src/rail_fence_cipher.c

@@ -0,0 +1,57 @@
+#include "rail_fence_cipher.h"
+#include <malloc.h>
+#include <string.h>
+#include <stdbool.h>
+
+/* See GNUmakefile below explanation
+ * https://github.com/braoult/exercism/blob/master/c/templates/GNUmakefile
+ */
+#if defined UNIT_TEST || defined DEBUG
+#include <stdio.h>
+#include <stdlib.h>
+#endif
+
+char *doit(char *t, size_t nr, int what)
+{
+    int tlen=strlen(t);
+    unsigned cchar=0, r;
+    char *res;
+
+    if (!(res=malloc(tlen+1)))
+        return NULL;
+    for (r=0; r<nr; ++r) {
+        bool flip=false;
+        int pchar=r;
+        while (pchar<tlen) {
+            if (what==ENCODE)
+                res[cchar]=t[pchar];
+            else
+                res[pchar]=t[cchar];
+            cchar++;
+            if (r>0 && r<nr-1) {
+                pchar+=flip ? r*2: (nr-r-1)*2;
+                flip=!flip;
+            } else {
+                pchar+=(nr-1)*2;
+            }
+
+        }
+    }
+    res[tlen]=0;
+    return res;
+}
+
+#ifdef UNIT_TEST
+int main(int ac, char **av)
+{
+    int arg=1;
+    int i;
+    char *p, *q;
+    for (; arg<ac-1; ++arg, ++arg) {
+        p=av[arg];
+        i=atoi(av[arg+1]);
+        printf("encode(%s, %d)=%s\n", p, i, q=encode(p, i));
+        printf("decode(%s, %d)=%s\n", q, i, decode(q, i));
+    }
+}
+#endif

c/rail-fence-cipher/src/rail_fence_cipher.h

@@ -0,0 +1,22 @@
+#ifndef RAIL_FENCE_CIPHER_H
+#define RAIL_FENCE_CIPHER_H
+
+#include <stddef.h>
+
+#define ENCODE 0
+#define DECODE 1
+
+char *doit(char *text, size_t rails, int action);
+
+#define encode(t, r) doit(t, r, ENCODE)
+#define decode(t, r) doit(t, r, DECODE)
+
+/* See GNUmakefile below for explanation
+ * https://github.com/braoult/exercism/blob/master/c/templates/GNUmakefile
+ */
+#ifdef  TESTALL
+#undef  TEST_IGNORE
+#define TEST_IGNORE() {}
+#endif
+
+#endif