1 files changed, 83 insertions, 0 deletions
diff --git a/third_party/heimdal/lib/hcrypto/libtommath/bn_mp_reduce.c b/third_party/heimdal/lib/hcrypto/libtommath/bn_mp_reduce.c
new file mode 100644
index 00000000000..3c669d491de
--- /dev/null
+++ b/third_party/heimdal/lib/hcrypto/libtommath/bn_mp_reduce.c
@@ -0,0 +1,83 @@
+#include "tommath_private.h"
+#ifdef BN_MP_REDUCE_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+/* reduces x mod m, assumes 0 < x < m**2, mu is
+ * precomputed via mp_reduce_setup.
+ * From HAC pp.604 Algorithm 14.42
+ */
+mp_err mp_reduce(mp_int *x, const mp_int *m, const mp_int *mu)
+{
+   mp_int  q;
+   mp_err  err;
+   int     um = m->used;
+
+   /* q = x */
+   if ((err = mp_init_copy(&q, x)) != MP_OKAY) {
+      return err;
+   }
+
+   /* q1 = x / b**(k-1)  */
+   mp_rshd(&q, um - 1);
+
+   /* according to HAC this optimization is ok */
+   if ((mp_digit)um > ((mp_digit)1 << (MP_DIGIT_BIT - 1))) {
+      if ((err = mp_mul(&q, mu, &q)) != MP_OKAY) {
+         goto CLEANUP;
+      }
+   } else if (MP_HAS(S_MP_MUL_HIGH_DIGS)) {
+      if ((err = s_mp_mul_high_digs(&q, mu, &q, um)) != MP_OKAY) {
+         goto CLEANUP;
+      }
+   } else if (MP_HAS(S_MP_MUL_HIGH_DIGS_FAST)) {
+      if ((err = s_mp_mul_high_digs_fast(&q, mu, &q, um)) != MP_OKAY) {
+         goto CLEANUP;
+      }
+   } else {
+      err = MP_VAL;
+      goto CLEANUP;
+   }
+
+   /* q3 = q2 / b**(k+1) */
+   mp_rshd(&q, um + 1);
+
+   /* x = x mod b**(k+1), quick (no division) */
+   if ((err = mp_mod_2d(x, MP_DIGIT_BIT * (um + 1), x)) != MP_OKAY) {
+      goto CLEANUP;
+   }
+
+   /* q = q * m mod b**(k+1), quick (no division) */
+   if ((err = s_mp_mul_digs(&q, m, &q, um + 1)) != MP_OKAY) {
+      goto CLEANUP;
+   }
+
+   /* x = x - q */
+   if ((err = mp_sub(x, &q, x)) != MP_OKAY) {
+      goto CLEANUP;
+   }
+
+   /* If x < 0, add b**(k+1) to it */
+   if (mp_cmp_d(x, 0uL) == MP_LT) {
+      mp_set(&q, 1uL);
+      if ((err = mp_lshd(&q, um + 1)) != MP_OKAY) {
+         goto CLEANUP;
+      }
+      if ((err = mp_add(x, &q, x)) != MP_OKAY) {
+         goto CLEANUP;
+      }
+   }
+
+   /* Back off if it's too big */
+   while (mp_cmp(x, m) != MP_LT) {
+      if ((err = s_mp_sub(x, m, x)) != MP_OKAY) {
+         goto CLEANUP;
+      }
+   }
+
+CLEANUP:
+   mp_clear(&q);
+
+   return err;
+}
+#endif