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+#include <tommath.h>
+#ifdef BN_S_MP_SQR_C
+/* 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, tomstdenis@gmail.com, http://math.libtomcrypt.com
+ */
+
+/* low level squaring, b = a*a, HAC pp.596-597, Algorithm 14.16 */
+int s_mp_sqr (mp_int * a, mp_int * b)
+{
+ mp_int t;
+ int res, ix, iy, pa;
+ mp_word r;
+ mp_digit u, tmpx, *tmpt;
+
+ pa = a->used;
+ if ((res = mp_init_size (&t, 2*pa + 1)) != MP_OKAY) {
+ return res;
+ }
+
+ /* default used is maximum possible size */
+ t.used = 2*pa + 1;
+
+ for (ix = 0; ix < pa; ix++) {
+ /* first calculate the digit at 2*ix */
+ /* calculate double precision result */
+ r = ((mp_word) t.dp[2*ix]) +
+ ((mp_word)a->dp[ix])*((mp_word)a->dp[ix]);
+
+ /* store lower part in result */
+ t.dp[ix+ix] = (mp_digit) (r & ((mp_word) MP_MASK));
+
+ /* get the carry */
+ u = (mp_digit)(r >> ((mp_word) DIGIT_BIT));
+
+ /* left hand side of A[ix] * A[iy] */
+ tmpx = a->dp[ix];
+
+ /* alias for where to store the results */
+ tmpt = t.dp + (2*ix + 1);
+
+ for (iy = ix + 1; iy < pa; iy++) {
+ /* first calculate the product */
+ r = ((mp_word)tmpx) * ((mp_word)a->dp[iy]);
+
+ /* now calculate the double precision result, note we use
+ * addition instead of *2 since it's easier to optimize
+ */
+ r = ((mp_word) *tmpt) + r + r + ((mp_word) u);
+
+ /* store lower part */
+ *tmpt++ = (mp_digit) (r & ((mp_word) MP_MASK));
+
+ /* get carry */
+ u = (mp_digit)(r >> ((mp_word) DIGIT_BIT));
+ }
+ /* propagate upwards */
+ while (u != ((mp_digit) 0)) {
+ r = ((mp_word) *tmpt) + ((mp_word) u);
+ *tmpt++ = (mp_digit) (r & ((mp_word) MP_MASK));
+ u = (mp_digit)(r >> ((mp_word) DIGIT_BIT));
+ }
+ }
+
+ mp_clamp (&t);
+ mp_exch (&t, b);
+ mp_clear (&t);
+ return MP_OKAY;
+}
+#endif