--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtommath/bn_mp_unpack.c	Thu Oct 15 19:55:15 2020 +0800
@@ -0,0 +1,49 @@
+#include "tommath_private.h"
+#ifdef BN_MP_UNPACK_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+/* based on gmp's mpz_import.
+ * see http://gmplib.org/manual/Integer-Import-and-Export.html
+ */
+mp_err mp_unpack(mp_int *rop, size_t count, mp_order order, size_t size,
+                 mp_endian endian, size_t nails, const void *op)
+{
+   mp_err err;
+   size_t odd_nails, nail_bytes, i, j;
+   unsigned char odd_nail_mask;
+
+   mp_zero(rop);
+
+   if (endian == MP_NATIVE_ENDIAN) {
+      MP_GET_ENDIANNESS(endian);
+   }
+
+   odd_nails = (nails % 8u);
+   odd_nail_mask = 0xff;
+   for (i = 0; i < odd_nails; ++i) {
+      odd_nail_mask ^= (unsigned char)(1u << (7u - i));
+   }
+   nail_bytes = nails / 8u;
+
+   for (i = 0; i < count; ++i) {
+      for (j = 0; j < (size - nail_bytes); ++j) {
+         unsigned char byte = *((const unsigned char *)op +
+                                (((order == MP_MSB_FIRST) ? i : ((count - 1u) - i)) * size) +
+                                ((endian == MP_BIG_ENDIAN) ? (j + nail_bytes) : (((size - 1u) - j) - nail_bytes)));
+
+         if ((err = mp_mul_2d(rop, (j == 0u) ? (int)(8u - odd_nails) : 8, rop)) != MP_OKAY) {
+            return err;
+         }
+
+         rop->dp[0] |= (j == 0u) ? (mp_digit)(byte & odd_nail_mask) : (mp_digit)byte;
+         rop->used  += 1;
+      }
+   }
+
+   mp_clamp(rop);
+
+   return MP_OKAY;
+}
+
+#endif