/* -*-c-*-
*
- * $Id: mp-jacobi.c,v 1.2 1999/12/10 23:19:02 mdw Exp $
+ * $Id: mp-jacobi.c,v 1.4 2000/12/06 20:31:33 mdw Exp $
*
* Compute Jacobi symbol
*
/*----- Revision history --------------------------------------------------*
*
* $Log: mp-jacobi.c,v $
+ * Revision 1.4 2000/12/06 20:31:33 mdw
+ * Add assertion to prevent crapness.
+ *
+ * Revision 1.3 2000/07/20 17:14:34 mdw
+ * Simplify by using @mp_odd@.
+ *
* Revision 1.2 1999/12/10 23:19:02 mdw
* Improve error-checking.
*
{
int s = 1;
+ assert(((void)"n must be odd in mp_jacobi", MP_LEN(n) && (n->v[0] & 1)));
+
/* --- Take copies of the arguments --- */
a = MP_COPY(a);
/* --- Main recursive mess, flattened out into something nice --- */
for (;;) {
+ mpw nn;
+ size_t e;
/* --- Some simple special cases --- */
MP_SHRINK(a);
-
if (MP_LEN(a) == 0) {
s = 0;
goto done;
}
- /* --- Find the power-of-two factor in @a@ --- */
-
- {
- mpscan sc;
- mpw nn;
- unsigned e;
-
- /* --- Scan for a set bit --- */
-
- MP_SCAN(&sc, a);
- e = 0;
- while (MP_STEP(&sc) && !MP_BIT(&sc))
- e++;
+ /* --- Main case with powers of two --- */
- /* --- Do the shift --- */
-
- if (e)
- a = mp_lsr(a, a, e);
-
- /* --- Maybe adjust the sign of @s@ --- */
-
- nn = n->v[0] & 7;
- if ((e & 1) && (nn == 3 || nn == 5))
- s = -s;
-
- if (MP_LEN(a) == 1 && a->v[0] == 1)
- goto done;
-
- if ((nn & 3) == 3 && (a->v[0] & 3) == 3)
- s = -s;
- }
+ a = mp_odd(a, a, &e);
+ nn = n->v[0] & 7;
+ if ((e & 1) && (nn == 3 || nn == 5))
+ s = -s;
+ if (MP_LEN(a) == 1 && a->v[0] == 1)
+ goto done;
+ if ((nn & 3) == 3 && (a->v[0] & 3) == 3)
+ s = -s;
/* --- Reduce and swap --- */