--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/bn_fast_s_mp_sqr.c	Mon May 31 18:25:22 2004 +0000
@@ -0,0 +1,139 @@
+/* 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>
+
+/* fast squaring
+ *
+ * This is the comba method where the columns of the product
+ * are computed first then the carries are computed.  This
+ * has the effect of making a very simple inner loop that
+ * is executed the most
+ *
+ * W2 represents the outer products and W the inner.
+ *
+ * A further optimizations is made because the inner
+ * products are of the form "A * B * 2".  The *2 part does
+ * not need to be computed until the end which is good
+ * because 64-bit shifts are slow!
+ *
+ * Based on Algorithm 14.16 on pp.597 of HAC.
+ *
+ */
+int fast_s_mp_sqr (mp_int * a, mp_int * b)
+{
+  int     olduse, newused, res, ix, pa;
+  mp_word W2[MP_WARRAY], W[MP_WARRAY];
+
+  /* calculate size of product and allocate as required */
+  pa = a->used;
+  newused = pa + pa + 1;
+  if (b->alloc < newused) {
+    if ((res = mp_grow (b, newused)) != MP_OKAY) {
+      return res;
+    }
+  }
+
+  /* zero temp buffer (columns)
+   * Note that there are two buffers.  Since squaring requires
+   * a outer and inner product and the inner product requires
+   * computing a product and doubling it (a relatively expensive
+   * op to perform n**2 times if you don't have to) the inner and
+   * outer products are computed in different buffers.  This way
+   * the inner product can be doubled using n doublings instead of
+   * n**2
+   */
+  memset (W,  0, newused * sizeof (mp_word));
+  memset (W2, 0, newused * sizeof (mp_word));
+
+  /* This computes the inner product.  To simplify the inner N**2 loop
+   * the multiplication by two is done afterwards in the N loop.
+   */
+  for (ix = 0; ix < pa; ix++) {
+    /* compute the outer product
+     *
+     * Note that every outer product is computed
+     * for a particular column only once which means that
+     * there is no need todo a double precision addition
+     * into the W2[] array.
+     */
+    W2[ix + ix] = ((mp_word)a->dp[ix]) * ((mp_word)a->dp[ix]);
+
+    {
+      register mp_digit tmpx, *tmpy;
+      register mp_word *_W;
+      register int iy;
+
+      /* copy of left side */
+      tmpx = a->dp[ix];
+
+      /* alias for right side */
+      tmpy = a->dp + (ix + 1);
+
+      /* the column to store the result in */
+      _W = W + (ix + ix + 1);
+
+      /* inner products */
+      for (iy = ix + 1; iy < pa; iy++) {
+          *_W++ += ((mp_word)tmpx) * ((mp_word)*tmpy++);
+      }
+    }
+  }
+
+  /* setup dest */
+  olduse  = b->used;
+  b->used = newused;
+
+  /* now compute digits
+   *
+   * We have to double the inner product sums, add in the
+   * outer product sums, propagate carries and convert
+   * to single precision.
+   */
+  {
+    register mp_digit *tmpb;
+
+    /* double first value, since the inner products are
+     * half of what they should be
+     */
+    W[0] += W[0] + W2[0];
+
+    tmpb = b->dp;
+    for (ix = 1; ix < newused; ix++) {
+      /* double/add next digit */
+      W[ix] += W[ix] + W2[ix];
+
+      /* propagate carry forwards [from the previous digit] */
+      W[ix] = W[ix] + (W[ix - 1] >> ((mp_word) DIGIT_BIT));
+
+      /* store the current digit now that the carry isn't
+       * needed
+       */
+      *tmpb++ = (mp_digit) (W[ix - 1] & ((mp_word) MP_MASK));
+    }
+    /* set the last value.  Note even if the carry is zero
+     * this is required since the next step will not zero
+     * it if b originally had a value at b->dp[2*a.used]
+     */
+    *tmpb++ = (mp_digit) (W[(newused) - 1] & ((mp_word) MP_MASK));
+
+    /* clear high digits of b if there were any originally */
+    for (; ix < olduse; ix++) {
+      *tmpb++ = 0;
+    }
+  }
+
+  mp_clamp (b);
+  return MP_OKAY;
+}