From aec422865a87fefe0f7276240c2f12c6faeffd27 Mon Sep 17 00:00:00 2001
From: mdw <mdw>
Date: Tue, 13 Sep 2005 15:23:21 +0000
Subject: [PATCH] New function to decide whether a share is already inserted.

---
 gfshare.c | 33 +++++++++++++++++++++++++++------
 gfshare.h | 15 ++++++++++++++-
 share.c   | 27 ++++++++++++++++++++++++---
 share.h   | 13 ++++++++++++-
 4 files changed, 77 insertions(+), 11 deletions(-)

diff --git a/gfshare.c b/gfshare.c
index a46f948..a7d7fb2 100644
--- 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;
diff --git a/gfshare.h b/gfshare.h
index a53d137..87c71a6 100644
--- a/gfshare.h
+++ b/gfshare.h
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: gfshare.h,v 1.7 2004/04/08 01:36:15 mdw Exp $
+ * $Id$
  *
  * Secret sharing over %$\gf{2^8}$%
  *
@@ -72,6 +72,8 @@ typedef struct gfshare {
 
 #define GFSHARE_INIT(t, sz) { t, 0, sz, 0 }
 
+#define GFSHARE_INDEX(s, i) ((s)->v[(i) * ((s)->sz + 1)])
+
 /*----- Functions provided ------------------------------------------------*/
 
 /* --- @gfshare_create@ --- *
@@ -133,6 +135,17 @@ extern void gfshare_mkshares(gfshare */*s*/, grand */*r*/,
 
 extern 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.
+ */
+
+extern int gfshare_addedp(gfshare */*s*/, unsigned /*x*/);
+
 /* --- @gfshare_add@ --- *
  *
  * Arguments:	@gfshare *s@ = pointer to sharing context
diff --git a/share.c b/share.c
index 23d730c..55f3b98 100644
--- 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;
diff --git a/share.h b/share.h
index 9683c07..d126983 100644
--- a/share.h
+++ b/share.h
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: share.h,v 1.4 2004/04/08 01:36:15 mdw Exp $
+ * $Id$
  *
  * Shamir's secret sharing
  *
@@ -134,6 +134,17 @@ extern void share_mkshares(share */*s*/, grand */*r*/, mp */*n*/);
 
 extern mp *share_get(share */*s*/, mp */*d*/, unsigned /*x*/);
 
+/* --- @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.
+ */
+
+extern int share_addedp(share */*s*/, unsigned /*x*/);
+
 /* --- @share_add@ --- *
  *
  * Arguments:	@share *s@ = pointer to sharing context
-- 
2.11.0