New function @mp_odd@ to extract powers of two from an integer. This is

common code from the Rabin-Miller test, RSA key recovery and modular
square-root extraction.

diff --git a/mp-arith.c b/mp-arith.c
index fe6a45d..c67fdd8 100644 (file)
--- a/mp-arith.c
+++ b/mp-arith.c
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: mp-arith.c,v 1.6 2000/06/17 11:45:09 mdw Exp $
+ * $Id: mp-arith.c,v 1.7 2000/06/22 19:02:53 mdw Exp $
  *
  * Basic arithmetic on multiprecision integers
  *
@@ -30,6 +30,11 @@
 /*----- Revision history --------------------------------------------------* 
  *
  * $Log: mp-arith.c,v $
+ * Revision 1.7  2000/06/22 19:02:53  mdw
+ * New function @mp_odd@ to extract powers of two from an integer.  This is
+ * common code from the Rabin-Miller test, RSA key recovery and modular
+ * square-root extraction.
+ *
  * Revision 1.6  2000/06/17 11:45:09  mdw
  * Major memory management overhaul.  Added arena support.  Use the secure
  * arena for secret integers.  Replace and improve the MP management macros
@@ -364,6 +369,49 @@ void mp_div(mp **qq, mp **rr, mp *a, mp *b)
   }
 }
 
+/* --- @mp_odd@ --- *
+ *
+ * Arguments:  @mp *d@ = pointer to destination integer
+ *             @mp *m@ = pointer to source integer
+ *             @size_t *s@ = where to store the power of 2
+ *
+ * Returns:    An odd integer integer %$t$% such that %$m = 2^s t$%.
+ *
+ * Use:                Computes a power of two and an odd integer which, when
+ *             multiplied, give a specified result.  This sort of thing is
+ *             useful in number theory quite often.
+ */
+
+mp *mp_odd(mp *d, mp *m, size_t *s)
+{
+  size_t ss = 0;
+  const mpw *v, *vl;
+
+  v = m->v;
+  vl = m->vl;
+  for (; !*v && v < vl; v++)
+    ss += MPW_BITS;
+  if (v >= vl)
+    ss = 0;
+  else {
+    mpw x = *v;
+    mpw mask = MPW_MAX;
+    unsigned z = MPW_BITS / 2;
+
+    while (z) {
+      mask >>= z;
+      if (!(x & mask)) {
+       x >>= z;
+       ss += z;
+      }
+      z >>= 1;
+    }
+  }
+
+  *s = ss;
+  return (mp_lsr(d, m, ss));
+}
+
 /*----- Test rig ----------------------------------------------------------*/
 
 #ifdef TEST_RIG
@@ -438,6 +486,31 @@ static int tdiv(dstr *v)
   return (ok);
 }
 
+static int todd(dstr *v)
+{
+  mp *a = *(mp **)v[0].buf;
+  size_t rs = *(uint32 *)v[1].buf;
+  mp *rt = *(mp **)v[2].buf;
+  int ok = 1;
+  mp *t;
+  size_t s;
+  t = mp_odd(MP_NEW, a, &s);
+  if (s != rs || MP_CMP(t, !=, rt)) {
+    ok = 0;
+    fprintf(stderr, "\n*** odd failed");
+    fputs("\n*** a  = ", stderr); mp_writefile(a, stderr, 10);
+    fprintf(stderr, "\n*** s  = %lu", (unsigned long)s);
+    fputs("\n*** t  = ", stderr); mp_writefile(t, stderr, 10);
+    fprintf(stderr, "\n*** rs = %lu", (unsigned long)rs);
+    fputs("\n*** rt = ", stderr); mp_writefile(rt, stderr, 10);
+    fputc('\n', stderr);
+  }
+  mp_drop(a);
+  mp_drop(rt);
+  mp_drop(t);
+  return (ok);
+}
+
 static test_chunk tests[] = {
   { "lsl", tlsl, { &type_mp, &type_mp, &type_mp, 0 } },
   { "lsr", tlsr, { &type_mp, &type_mp, &type_mp, 0 } },
@@ -445,6 +518,7 @@ static test_chunk tests[] = {
   { "sub", tsub, { &type_mp, &type_mp, &type_mp, 0 } },
   { "mul", tmul, { &type_mp, &type_mp, &type_mp, 0 } },
   { "div", tdiv, { &type_mp, &type_mp, &type_mp, &type_mp, 0 } },
+  { "odd", todd, { &type_mp, &type_uint32, &type_mp, 0 } },
   { 0, 0, { 0 } },
 };