1 files changed, 102 insertions, 0 deletions
diff --git a/third_party/heimdal/lib/hcrypto/libtommath/bn_mp_montgomery_reduce.c b/third_party/heimdal/lib/hcrypto/libtommath/bn_mp_montgomery_reduce.c
new file mode 100644
index 0000000..ffe8341
--- /dev/null
+++ b/third_party/heimdal/lib/hcrypto/libtommath/bn_mp_montgomery_reduce.c
@@ -0,0 +1,102 @@
+#include "tommath_private.h"
+#ifdef BN_MP_MONTGOMERY_REDUCE_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+/* computes xR**-1 == x (mod N) via Montgomery Reduction */
+mp_err mp_montgomery_reduce(mp_int *x, const mp_int *n, mp_digit rho)
+{
+   int      ix, digs;
+   mp_err   err;
+   mp_digit mu;
+
+   /* can the fast reduction [comba] method be used?
+    *
+    * Note that unlike in mul you're safely allowed *less*
+    * than the available columns [255 per default] since carries
+    * are fixed up in the inner loop.
+    */
+   digs = (n->used * 2) + 1;
+   if ((digs < MP_WARRAY) &&
+       (x->used <= MP_WARRAY) &&
+       (n->used < MP_MAXFAST)) {
+      return s_mp_montgomery_reduce_fast(x, n, rho);
+   }
+
+   /* grow the input as required */
+   if (x->alloc < digs) {
+      if ((err = mp_grow(x, digs)) != MP_OKAY) {
+         return err;
+      }
+   }
+   x->used = digs;
+
+   for (ix = 0; ix < n->used; ix++) {
+      /* mu = ai * rho mod b
+       *
+       * The value of rho must be precalculated via
+       * montgomery_setup() such that
+       * it equals -1/n0 mod b this allows the
+       * following inner loop to reduce the
+       * input one digit at a time
+       */
+      mu = (mp_digit)(((mp_word)x->dp[ix] * (mp_word)rho) & MP_MASK);
+
+      /* a = a + mu * m * b**i */
+      {
+         int iy;
+         mp_digit *tmpn, *tmpx, u;
+         mp_word r;
+
+         /* alias for digits of the modulus */
+         tmpn = n->dp;
+
+         /* alias for the digits of x [the input] */
+         tmpx = x->dp + ix;
+
+         /* set the carry to zero */
+         u = 0;
+
+         /* Multiply and add in place */
+         for (iy = 0; iy < n->used; iy++) {
+            /* compute product and sum */
+            r       = ((mp_word)mu * (mp_word)*tmpn++) +
+                      (mp_word)u + (mp_word)*tmpx;
+
+            /* get carry */
+            u       = (mp_digit)(r >> (mp_word)MP_DIGIT_BIT);
+
+            /* fix digit */
+            *tmpx++ = (mp_digit)(r & (mp_word)MP_MASK);
+         }
+         /* At this point the ix'th digit of x should be zero */
+
+
+         /* propagate carries upwards as required*/
+         while (u != 0u) {
+            *tmpx   += u;
+            u        = *tmpx >> MP_DIGIT_BIT;
+            *tmpx++ &= MP_MASK;
+         }
+      }
+   }
+
+   /* at this point the n.used'th least
+    * significant digits of x are all zero
+    * which means we can shift x to the
+    * right by n.used digits and the
+    * residue is unchanged.
+    */
+
+   /* x = x/b**n.used */
+   mp_clamp(x);
+   mp_rshd(x, n->used);
+
+   /* if x >= n then x = x - n */
+   if (mp_cmp_mag(x, n) != MP_LT) {
+      return s_mp_sub(x, n, x);
+   }
+
+   return MP_OKAY;
+}
+#endif