fizzbuzz puzzle

packages/fizzbuzz/src/fizzbuzz.c

@@ -0,0 +1,85 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+/*
+ * How this works:
+ *
+ * You have to provide this with the output of a fizzbuzz program to get
+ * it to decode the token.
+ *
+ * Provide the encoded token on fd 3, and it will output the decode
+ * provided correct input.  If you provided the decoded token, it will
+ * encode it.  In other words, encode(x) = decode(x).
+ *
+ *
+ * Here's a fizzbuzz program in bourne shell:
+ *
+ *   for i in $(seq 100); do
+ *      if [ $(expr $i % 15) = 0 ]; then
+ *          echo 'FizzBuzz'
+ *      elif [ $(expr $i % 3) = 0 ]; then
+ *          echo 'Fizz'
+ *      elif [ $(expr $i % 5) = 0 ]; then
+ *          echo 'Buzz'
+ *      else
+ *          echo $i
+ *      fi
+ *  done
+ * 
+ */
+
+char craptable[] = {
+  0x64, 0xd4, 0x11, 0x55, 0x50, 0x16, 0x61, 0x02,
+  0xf7, 0xfd, 0x63, 0x36, 0xd9, 0xa6, 0xf2, 0x29,
+  0xad, 0xfb, 0xed, 0x7a, 0x06, 0x91, 0xe7, 0x67,
+  0x80, 0xb6, 0x53, 0x2c, 0x43, 0xf9, 0x3c, 0xf2,
+  0x83, 0x5c, 0x25, 0xee, 0x21
+};
+
+int
+main(int argc, char *argv[])
+{
+  int    i;
+  char   token[100];
+  size_t tokenlen;
+
+  {
+    FILE *tokenin = fdopen(3, "r");
+
+    if (! tokenin) {
+      printf("Somebody didn't read the instructions.\n");
+      return 1;
+    }
+    
+    tokenlen = fread(token, 1, sizeof(token), tokenin);
+    fclose(tokenin);
+  }
+  
+
+  for (i=1; i <= 100; i += 1) {
+    char l[100];
+
+    fgets(l, sizeof(l), stdin);
+
+    if (0 == i % 15) {
+      if (0 != strcmp("FizzBuzz\n", l)) break;
+    } else if (0 == i % 3) {
+      if (0 != strcmp("Fizz\n", l)) break;
+    } else if (0 == i % 5) {
+      if (0 != strcmp("Buzz\n", l)) break;
+    } else {
+      if (atoi(l) != i) break;
+    }
+
+    token[i % tokenlen] ^= i;
+    token[i % tokenlen] ^= craptable[i % sizeof(craptable)];
+  }
+
+  if (101 == i) {
+    fwrite(token, tokenlen, 1, stdout);
+  } else {
+    printf("Next time, FizzBuzz me.\n");
+  }
+
+  return 0;
+}