catcrypt: Implement symmetric key-encapsulation and signature schemes.

[u/mdw/catacomb] / gfshare.c

diff --git a/gfshare.c b/gfshare.c
index a46f948..a7d7fb2 100644 (file)
--- a/gfshare.c
+++ b/gfshare.c
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: gfshare.c,v 1.9 2004/04/08 01:36:15 mdw Exp $
+ * $Id$
  *
  * Secret sharing over %$\gf{2^8}$%
  *
@@ -142,6 +142,26 @@ void gfshare_get(gfshare *s, unsigned x, void *buf)
   }
 }
 
+/* --- @gfshare_addedp@ --- *
+ *
+ * Arguments:  @gfshare *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 gfshare_addedp(gfshare *s, unsigned x)
+{
+  unsigned i;
+
+  for (i = 0; i < s->i; i++) {
+    if (GFSHARE_INDEX(s, i) == x + 1)
+      return (1);
+  }
+  return (0);
+}
+
 /* --- @gfshare_add@ --- *
  *
  * Arguments:  @gfshare *s@ = pointer to sharing context
@@ -158,6 +178,9 @@ unsigned gfshare_add(gfshare *s, unsigned x, const void *y)
 {
   octet *p;
 
+  assert(((void)"Share context is full", s->i < s->t));
+  assert(((void)"Share already present", !gfshare_addedp(s, x)));
+
   /* --- If no vector has been allocated, create one --- */
 
   if (!s->v) {
@@ -165,11 +188,9 @@ unsigned gfshare_add(gfshare *s, unsigned x, const void *y)
     s->i = 0;
   }
 
-  assert(((void)"Share context is full", s->i < s->t));
-
   /* --- Store the share in the vector --- */
 
-  p = s->v + s->i * (s->sz + 1);
+  p = &GFSHARE_INDEX(s, s->i);
   *p++ = x + 1;
   memcpy(p, y, s->sz);
   s->i++;
@@ -204,7 +225,7 @@ void gfshare_combine(gfshare *s, void *buf)
 
   for (i = 0; i < s->t; i++) {
     octet *p = buf;
-    octet *q = s->v + i * (s->sz + 1);
+    octet *q = &GFSHARE_INDEX(s, i);
     unsigned c = 0, ci = 0;
 
     /* --- Compute the magic coefficient --- */
@@ -213,7 +234,7 @@ void gfshare_combine(gfshare *s, void *buf)
     for (j = 0; j < s->t; j++) {
       if (i == j)
        continue;
-      xj = s->v[j * (s->sz + 1)];
+      xj = GFSHARE_INDEX(s, j);
       c += gflog[xj];
       if (c >= 0xff)
        c -= 0xff;