-#include <tommath.h>
+#include "tommath_private.h"
#ifdef BN_MP_MONTGOMERY_REDUCE_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://libtom.org
- */
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
/* computes xR**-1 == x (mod N) via Montgomery Reduction */
-int
-mp_montgomery_reduce (mp_int * x, mp_int * n, mp_digit rho)
+mp_err mp_montgomery_reduce(mp_int *x, const mp_int *n, mp_digit rho)
{
- int ix, res, digs;
- 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) &&
- n->used <
- (1 << ((CHAR_BIT * sizeof (mp_word)) - (2 * DIGIT_BIT)))) {
- return fast_mp_montgomery_reduce (x, n, rho);
- }
-
- /* grow the input as required */
- if (x->alloc < digs) {
- if ((res = mp_grow (x, digs)) != MP_OKAY) {
- return res;
- }
- }
- 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 */
- {
- register int iy;
- register mp_digit *tmpn, *tmpx, u;
- register 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) DIGIT_BIT));
-
- /* fix digit */
- *tmpx++ = (mp_digit)(r & ((mp_word) MP_MASK));
+ 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;
}
- /* At this point the ix'th digit of x should be zero */
+ }
+ 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.
+ */
- /* propagate carries upwards as required*/
- while (u) {
- *tmpx += u;
- u = *tmpx >> 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;
+ /* 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
-
-/* $Source: /cvs/libtom/libtommath/bn_mp_montgomery_reduce.c,v $ */
-/* $Revision: 1.4 $ */
-/* $Date: 2006/12/28 01:25:13 $ */
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