X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/d34decd2b2b88240cf4ca68a2a5feb7bf36de6e7..22bab86c9df047bdd258283c6567821319ba7a6f:/mp-arith.c

diff --git a/mp-arith.c b/mp-arith.c
index fe6a45d..96fdeb8 100644
--- 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 1.8 2000/10/08 12:02:21 mdw Exp $
  *
  * Basic arithmetic on multiprecision integers
  *
@@ -30,6 +30,14 @@
 /*----- Revision history --------------------------------------------------* 
  *
  * $Log: mp-arith.c,v $
+ * Revision 1.8  2000/10/08 12:02:21  mdw
+ * Use @MP_EQ@ instead of @MP_CMP@.
+ *
+ * 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
@@ -138,6 +146,15 @@ mp *mp_lsr(mp *d, mp *a, size_t n)
   return (d);
 }
 
+/* --- @mp_eq@ --- *
+ *
+ * Arguments:	@const mp *a, *b@ = two numbers
+ *
+ * Returns:	Nonzero if the numbers are equal.
+ */
+
+int mp_eq(const mp *a, const mp *b) { return (MP_EQ(a, b)); }
+
 /* --- @mp_cmp@ --- *
  *
  * Arguments:	@const mp *a, *b@ = two numbers
@@ -364,13 +381,56 @@ 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
 
 static int verify(const char *op, mp *expect, mp *result, mp *a, mp *b)
 {
-  if (MP_CMP(expect, !=, result)) {
+  if (!MP_EQ(expect, result)) {
     fprintf(stderr, "\n*** %s failed", op);
     fputs("\n*** a      = ", stderr); mp_writefile(a, stderr, 10);
     fputs("\n*** b      = ", stderr); mp_writefile(b, stderr, 10);
@@ -438,6 +498,31 @@ 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_EQ(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 +530,7 @@ 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 } },
 };