From 9f7d85794539cd03a195dca3ab75ba0db98d5b3f Mon Sep 17 00:00:00 2001
From: Dan Buch <daniel.buch@gmail.com>
Date: Fri, 15 Apr 2016 22:41:28 -0400
Subject: [PATCH] ex23

---
 lcthw-remnants-2/ex23.c | 109 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 109 insertions(+)
 create mode 100644 lcthw-remnants-2/ex23.c

diff --git a/lcthw-remnants-2/ex23.c b/lcthw-remnants-2/ex23.c
new file mode 100644
index 0000000..d0acc5d
--- /dev/null
+++ b/lcthw-remnants-2/ex23.c
@@ -0,0 +1,109 @@
+#include <stdio.h>
+#include <string.h>
+#include "dbg.h"
+
+int normal_copy(char *from, char *to, int count)
+{
+  int i = 0;
+
+  for(i = 0; i < count; i++) {
+    to[i] = from[i];
+  }
+
+  return i;
+}
+
+int duffs_device(char *from, char *to, int count)
+{
+  {
+    int n = (count + 7) / 8;
+    debug("n=%d, (count %% 8)=%d", n, count % 8);
+
+    switch(count % 8) {
+      case 0: do { *to++ = *from++;
+                case 7: *to++ = *from++;
+                case 6: *to++ = *from++;
+                case 5: *to++ = *from++;
+                case 4: *to++ = *from++;
+                case 3: *to++ = *from++;
+                case 2: *to++ = *from++;
+                case 1: *to++ = *from++;
+              } while(--n > 0);
+    }
+  }
+
+  return count;
+}
+
+int zeds_device(char *from, char *to, int count)
+{
+  {
+    int n = (count + 7) / 8;
+
+    switch(count % 8) {
+      case 0:
+again: *to++ = *from++;
+      case 7: *to++ = *from++;
+      case 6: *to++ = *from++;
+      case 5: *to++ = *from++;
+      case 4: *to++ = *from++;
+      case 3: *to++ = *from++;
+      case 2: *to++ = *from++;
+      case 1: *to++ = *from++;
+              if(--n > 0) goto again;
+    }
+  }
+
+  return count;
+}
+
+int valid_copy(char *data, int count, char expects)
+{
+  int i = 0;
+  for(i = 0; i < count; i++) {
+    if(data[i] != expects) {
+      log_err("[%d] %c != %c", i, data[i], expects);
+      return 0;
+    }
+  }
+
+  return 1;
+}
+
+int main(int argc, char *argv[])
+{
+  char from[1000] = {'a'};
+  char to[1000] = {'c'};
+  int rc = 0;
+
+  // setup the from to have some stuff
+  memset(from, 'x', 1000);
+  // set it to a failure mode
+  memset(to, 'y', 1000);
+  check(valid_copy(to, 1000, 'y'), "Not initialized right.");
+
+  // use normal copy to
+  rc = normal_copy(from, to, 1000);
+  check(rc == 1000, "Normal copy failed: %d", rc);
+  check(valid_copy(to, 1000, 'x'), "Normal copy failed.");
+
+  // reset
+  memset(to, 'y', 1000);
+
+  // duffs version
+  rc = duffs_device(from, to, 1000);
+  check(rc == 1000, "Duff's deice failed: %d", rc);
+  check(valid_copy(to, 1000, 'x'), "Duff's deice failed copy.");
+
+  // reset
+  memset(to, 'y', 1000);
+
+  // my version
+  rc = zeds_device(from, to, 1000);
+  check(rc == 1000, "Zed's device failed: %d", rc);
+  check(valid_copy(to, 1000, 'x'), "Zed's device failed copy.");
+
+  return 0;
+error:
+  return 1;
+}