Add faster, optional sqr routine for internal LibTomMath

[libeap.git] / src / tls / libtommath.c

diff --git a/src/tls/libtommath.c b/src/tls/libtommath.c
index 374feb0..ea000f0 100644 (file)
--- a/src/tls/libtommath.c
+++ b/src/tls/libtommath.c
@@ -36,6 +36,11 @@
 #define BN_MP_MUL_2_C
 #endif /* LTM_FAST_EXPTMOD */
 
+#ifdef LTM_FAST_SQR
+/* Include faster sqr at the cost of about 0.5 kB in code */
+#define BN_FAST_S_MP_SQR_C
+#endif /* LTM_FAST_SQR */
+
 /* Current uses do not require support for negative exponent in exptmod, so we
  * can save about 1.5 kB in leaving out invmod. */
 #define LTM_NO_NEG_EXP
@@ -153,6 +158,9 @@ static int mp_init_size(mp_int * a, int size);
 #ifdef BN_MP_EXPTMOD_FAST_C
 static int mp_exptmod_fast (mp_int * G, mp_int * X, mp_int * P, mp_int * Y, int redmode);
 #endif /* BN_MP_EXPTMOD_FAST_C */
+#ifdef BN_FAST_S_MP_SQR_C
+static int fast_s_mp_sqr (mp_int * a, mp_int * b);
+#endif /* BN_FAST_S_MP_SQR_C */
 
 
 
@@ -2988,3 +2996,99 @@ LBL_M:
   return err;
 }
 #endif
+
+
+#ifdef BN_FAST_S_MP_SQR_C
+/* the jist of squaring...
+ * you do like mult except the offset of the tmpx [one that 
+ * starts closer to zero] can't equal the offset of tmpy.  
+ * So basically you set up iy like before then you min it with
+ * (ty-tx) so that it never happens.  You double all those 
+ * you add in the inner loop
+
+After that loop you do the squares and add them in.
+*/
+
+static int fast_s_mp_sqr (mp_int * a, mp_int * b)
+{
+  int       olduse, res, pa, ix, iz;
+  mp_digit   W[MP_WARRAY], *tmpx;
+  mp_word   W1;
+
+  /* grow the destination as required */
+  pa = a->used + a->used;
+  if (b->alloc < pa) {
+    if ((res = mp_grow (b, pa)) != MP_OKAY) {
+      return res;
+    }
+  }
+
+  /* number of output digits to produce */
+  W1 = 0;
+  for (ix = 0; ix < pa; ix++) { 
+      int      tx, ty, iy;
+      mp_word  _W;
+      mp_digit *tmpy;
+
+      /* clear counter */
+      _W = 0;
+
+      /* get offsets into the two bignums */
+      ty = MIN(a->used-1, ix);
+      tx = ix - ty;
+
+      /* setup temp aliases */
+      tmpx = a->dp + tx;
+      tmpy = a->dp + ty;
+
+      /* this is the number of times the loop will iterrate, essentially
+         while (tx++ < a->used && ty-- >= 0) { ... }
+       */
+      iy = MIN(a->used-tx, ty+1);
+
+      /* now for squaring tx can never equal ty 
+       * we halve the distance since they approach at a rate of 2x
+       * and we have to round because odd cases need to be executed
+       */
+      iy = MIN(iy, (ty-tx+1)>>1);
+
+      /* execute loop */
+      for (iz = 0; iz < iy; iz++) {
+         _W += ((mp_word)*tmpx++)*((mp_word)*tmpy--);
+      }
+
+      /* double the inner product and add carry */
+      _W = _W + _W + W1;
+
+      /* even columns have the square term in them */
+      if ((ix&1) == 0) {
+         _W += ((mp_word)a->dp[ix>>1])*((mp_word)a->dp[ix>>1]);
+      }
+
+      /* store it */
+      W[ix] = (mp_digit)(_W & MP_MASK);
+
+      /* make next carry */
+      W1 = _W >> ((mp_word)DIGIT_BIT);
+  }
+
+  /* setup dest */
+  olduse  = b->used;
+  b->used = a->used+a->used;
+
+  {
+    mp_digit *tmpb;
+    tmpb = b->dp;
+    for (ix = 0; ix < pa; ix++) {
+      *tmpb++ = W[ix] & MP_MASK;
+    }
+
+    /* clear unused digits [that existed in the old copy of c] */
+    for (; ix < olduse; ix++) {
+      *tmpb++ = 0;
+    }
+  }
+  mp_clamp (b);
+  return MP_OKAY;
+}
+#endif