--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtommath/bn_mp_pack.c	Fri Jun 26 21:07:34 2020 +0800
@@ -0,0 +1,69 @@
+#include "tommath_private.h"
+#ifdef BN_MP_PACK_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+/* based on gmp's mpz_export.
+ * see http://gmplib.org/manual/Integer-Import-and-Export.html
+ */
+mp_err mp_pack(void *rop, size_t maxcount, size_t *written, mp_order order, size_t size,
+               mp_endian endian, size_t nails, const mp_int *op)
+{
+   mp_err err;
+   size_t odd_nails, nail_bytes, i, j, count;
+   unsigned char odd_nail_mask;
+
+   mp_int t;
+
+   count = mp_pack_count(op, nails, size);
+
+   if (count > maxcount) {
+      return MP_BUF;
+   }
+
+   if ((err = mp_init_copy(&t, op)) != MP_OKAY) {
+      return err;
+   }
+
+   if (endian == MP_NATIVE_ENDIAN) {
+      MP_GET_ENDIANNESS(endian);
+   }
+
+   odd_nails = (nails % 8u);
+   odd_nail_mask = 0xff;
+   for (i = 0u; i < odd_nails; ++i) {
+      odd_nail_mask ^= (unsigned char)(1u << (7u - i));
+   }
+   nail_bytes = nails / 8u;
+
+   for (i = 0u; i < count; ++i) {
+      for (j = 0u; j < size; ++j) {
+         unsigned char *byte = (unsigned char *)rop +
+                               (((order == MP_LSB_FIRST) ? i : ((count - 1u) - i)) * size) +
+                               ((endian == MP_LITTLE_ENDIAN) ? j : ((size - 1u) - j));
+
+         if (j >= (size - nail_bytes)) {
+            *byte = 0;
+            continue;
+         }
+
+         *byte = (unsigned char)((j == ((size - nail_bytes) - 1u)) ? (t.dp[0] & odd_nail_mask) : (t.dp[0] & 0xFFuL));
+
+         if ((err = mp_div_2d(&t, (j == ((size - nail_bytes) - 1u)) ? (int)(8u - odd_nails) : 8, &t, NULL)) != MP_OKAY) {
+            goto LBL_ERR;
+         }
+
+      }
+   }
+
+   if (written != NULL) {
+      *written = count;
+   }
+   err = MP_OKAY;
+
+LBL_ERR:
+   mp_clear(&t);
+   return err;
+}
+
+#endif