catcrypt: Implement symmetric key-encapsulation and signature schemes.

[u/mdw/catacomb] / share.c

diff --git a/share.c b/share.c
index 23d730c..55f3b98 100644 (file)
--- a/share.c
+++ b/share.c
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: share.c,v 1.7 2004/04/08 01:36:15 mdw Exp $
+ * $Id$
  *
  * Shamir's secret sharing
  *
@@ -172,6 +172,26 @@ mp *share_get(share *s, mp *d, unsigned x)
   return (d);
 }
 
+/* --- @share_addedp@ --- *
+ *
+ * Arguments:  @share *s@ = pointer to sharing context
+ *             @unsigned x@ = which share number to check
+ *
+ * Returns:    Nonzero if share @x@ has been added already, zero if it
+ *             hasn't.
+ */
+
+int share_addedp(share *s, unsigned x)
+{
+  unsigned i;
+
+  for (i = 0; i < s->i; i++) {
+    if (s->v[i].x == x + 1)
+      return (1);
+  }
+  return (0);
+}
+
 /* --- @share_add@ --- *
  *
  * Arguments:  @share *s@ = pointer to sharing context
@@ -186,6 +206,9 @@ mp *share_get(share *s, mp *d, unsigned x)
 
 unsigned share_add(share *s, unsigned x, mp *y)
 {
+  assert(((void)"Share context is full", s->i < s->t));
+  assert(((void)"Share already present", !share_addedp(s, x)));
+
   /* --- If no vector has been allocated, create one --- */
 
   if (!s->v) {
@@ -196,8 +219,6 @@ unsigned share_add(share *s, unsigned x, mp *y)
       s->v[i].y = 0;
   }
 
-  assert(((void)"Share context is full", s->i < s->t));
-
   /* --- Store the share in the vector --- */
 
   s->v[s->i].x = x + 1;