--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/bn_mp_jacobi.c	Mon May 31 18:25:22 2004 +0000
@@ -0,0 +1,99 @@
+/* LibTomMath, multiple-precision integer library -- Tom St Denis
+ *
+ * LibTomMath is a library that provides multiple-precision
+ * integer arithmetic as well as number theoretic functionality.
+ *
+ * The library was designed directly after the MPI library by
+ * Michael Fromberger but has been written from scratch with
+ * additional optimizations in place.
+ *
+ * The library is free for all purposes without any express
+ * guarantee it works.
+ *
+ * Tom St Denis, [email protected], http://math.libtomcrypt.org
+ */
+#include <tommath.h>
+
+/* computes the jacobi c = (a | n) (or Legendre if n is prime)
+ * HAC pp. 73 Algorithm 2.149
+ */
+int mp_jacobi (mp_int * a, mp_int * p, int *c)
+{
+  mp_int  a1, p1;
+  int     k, s, r, res;
+  mp_digit residue;
+
+  /* if p <= 0 return MP_VAL */
+  if (mp_cmp_d(p, 0) != MP_GT) {
+     return MP_VAL;
+  }
+
+  /* step 1.  if a == 0, return 0 */
+  if (mp_iszero (a) == 1) {
+    *c = 0;
+    return MP_OKAY;
+  }
+
+  /* step 2.  if a == 1, return 1 */
+  if (mp_cmp_d (a, 1) == MP_EQ) {
+    *c = 1;
+    return MP_OKAY;
+  }
+
+  /* default */
+  s = 0;
+
+  /* step 3.  write a = a1 * 2**k  */
+  if ((res = mp_init_copy (&a1, a)) != MP_OKAY) {
+    return res;
+  }
+
+  if ((res = mp_init (&p1)) != MP_OKAY) {
+    goto __A1;
+  }
+
+  /* divide out larger power of two */
+  k = mp_cnt_lsb(&a1);
+  if ((res = mp_div_2d(&a1, k, &a1, NULL)) != MP_OKAY) {
+     goto __P1;
+  }
+
+  /* step 4.  if e is even set s=1 */
+  if ((k & 1) == 0) {
+    s = 1;
+  } else {
+    /* else set s=1 if p = 1/7 (mod 8) or s=-1 if p = 3/5 (mod 8) */
+    residue = p->dp[0] & 7;
+
+    if (residue == 1 || residue == 7) {
+      s = 1;
+    } else if (residue == 3 || residue == 5) {
+      s = -1;
+    }
+  }
+
+  /* step 5.  if p == 3 (mod 4) *and* a1 == 3 (mod 4) then s = -s */
+  if ( ((p->dp[0] & 3) == 3) && ((a1.dp[0] & 3) == 3)) {
+    s = -s;
+  }
+
+  /* if a1 == 1 we're done */
+  if (mp_cmp_d (&a1, 1) == MP_EQ) {
+    *c = s;
+  } else {
+    /* n1 = n mod a1 */
+    if ((res = mp_mod (p, &a1, &p1)) != MP_OKAY) {
+      goto __P1;
+    }
+    if ((res = mp_jacobi (&p1, &a1, &r)) != MP_OKAY) {
+      goto __P1;
+    }
+    *c = s * r;
+  }
+
+  /* done */
+  res = MP_OKAY;
+__P1:mp_clear (&p1);
+__A1:mp_clear (&a1);
+  return res;
+}