+ BN_CTX_end(ctx);
+ return (ret);
+}
+
+#ifdef MONT_WORD
+static int BN_from_montgomery_word(BIGNUM *ret, BIGNUM *r, BN_MONT_CTX *mont)
+{
+ BIGNUM *n;
+ BN_ULONG *ap, *np, *rp, n0, v, carry;
+ int nl, max, i;
+
+ n = &(mont->N);
+ nl = n->top;
+ if (nl == 0) {
+ ret->top = 0;
+ return (1);
+ }
+
+ max = (2 * nl); /* carry is stored separately */
+ if (bn_wexpand(r, max) == NULL)
+ return (0);
+
+ r->neg ^= n->neg;
+ np = n->d;
+ rp = r->d;
+
+ /* clear the top words of T */
+ i = max - r->top;
+ if (i)
+ memset(&rp[r->top], 0, sizeof(*rp) * i);
+
+ r->top = max;
+ n0 = mont->n0[0];
+
+ for (carry = 0, i = 0; i < nl; i++, rp++) {
+ v = bn_mul_add_words(rp, np, nl, (rp[0] * n0) & BN_MASK2);
+ v = (v + carry + rp[nl]) & BN_MASK2;
+ carry |= (v != rp[nl]);
+ carry &= (v <= rp[nl]);
+ rp[nl] = v;
+ }
+
+ if (bn_wexpand(ret, nl) == NULL)
+ return (0);
+ ret->top = nl;
+ ret->neg = r->neg;
+
+ rp = ret->d;
+ ap = &(r->d[nl]);
+
+# define BRANCH_FREE 1
+# if BRANCH_FREE
+ {
+ BN_ULONG *nrp;
+ size_t m;
+
+ v = bn_sub_words(rp, ap, np, nl) - carry;
+ /*
+ * if subtraction result is real, then trick unconditional memcpy
+ * below to perform in-place "refresh" instead of actual copy.
+ */
+ m = (0 - (size_t)v);
+ nrp =
+ (BN_ULONG *)(((PTR_SIZE_INT) rp & ~m) | ((PTR_SIZE_INT) ap & m));
+
+ for (i = 0, nl -= 4; i < nl; i += 4) {
+ BN_ULONG t1, t2, t3, t4;
+
+ t1 = nrp[i + 0];
+ t2 = nrp[i + 1];
+ t3 = nrp[i + 2];
+ ap[i + 0] = 0;
+ t4 = nrp[i + 3];
+ ap[i + 1] = 0;
+ rp[i + 0] = t1;
+ ap[i + 2] = 0;
+ rp[i + 1] = t2;
+ ap[i + 3] = 0;
+ rp[i + 2] = t3;
+ rp[i + 3] = t4;
+ }
+ for (nl += 4; i < nl; i++)
+ rp[i] = nrp[i], ap[i] = 0;
+ }
+# else
+ if (bn_sub_words(rp, ap, np, nl) - carry)
+ memcpy(rp, ap, nl * sizeof(BN_ULONG));
+# endif
+ bn_correct_top(r);
+ bn_correct_top(ret);
+ bn_check_top(ret);
+
+ return (1);
+}
+#endif /* MONT_WORD */
+
+int BN_from_montgomery(BIGNUM *ret, const BIGNUM *a, BN_MONT_CTX *mont,
+ BN_CTX *ctx)
+{
+ int retn = 0;
+#ifdef MONT_WORD
+ BIGNUM *t;
+
+ BN_CTX_start(ctx);
+ if ((t = BN_CTX_get(ctx)) && BN_copy(t, a))
+ retn = BN_from_montgomery_word(ret, t, mont);
+ BN_CTX_end(ctx);
+#else /* !MONT_WORD */
+ BIGNUM *t1, *t2;
+
+ BN_CTX_start(ctx);
+ t1 = BN_CTX_get(ctx);
+ t2 = BN_CTX_get(ctx);
+ if (t1 == NULL || t2 == NULL)
+ goto err;
+
+ if (!BN_copy(t1, a))
+ goto err;
+ BN_mask_bits(t1, mont->ri);
+
+ if (!BN_mul(t2, t1, &mont->Ni, ctx))
+ goto err;
+ BN_mask_bits(t2, mont->ri);
+
+ if (!BN_mul(t1, t2, &mont->N, ctx))
+ goto err;
+ if (!BN_add(t2, a, t1))
+ goto err;
+ if (!BN_rshift(ret, t2, mont->ri))
+ goto err;
+
+ if (BN_ucmp(ret, &(mont->N)) >= 0) {
+ if (!BN_usub(ret, ret, &(mont->N)))
+ goto err;
+ }
+ retn = 1;
+ bn_check_top(ret);
+ err:
+ BN_CTX_end(ctx);
+#endif /* MONT_WORD */
+ return (retn);
+}