mp_pack.c

   1 #include "tommath_private.h"
   2 #ifdef MP_PACK_C
   3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
   4 /* SPDX-License-Identifier: Unlicense */
   5
   6 /* based on gmp's mpz_export.
   7  * see http://gmplib.org/manual/Integer-Import-and-Export.html
   8  */
   9 mp_err mp_pack(void *rop, size_t maxcount, size_t *written, mp_order order, size_t size,
  10                mp_endian endian, size_t nails, const mp_int *op)
  11 {
  12    mp_err err;
  13    size_t odd_nails, nail_bytes, i, j, count;
  14    uint8_t odd_nail_mask;
  15
  16    mp_int t;
  17
  18    count = mp_pack_count(op, nails, size);
  19
  20    if (count > maxcount) {
  21       return MP_BUF;
  22    }
  23
  24    if ((err = mp_init_copy(&t, op)) != MP_OKAY) {
  25       return err;
  26    }
  27
  28    if (endian == MP_NATIVE_ENDIAN) {
  29       MP_GET_ENDIANNESS(endian);
  30    }
  31
  32    odd_nails = (nails % 8u);
  33    odd_nail_mask = 0xff;
  34    for (i = 0u; i < odd_nails; ++i) {
  35       odd_nail_mask ^= (uint8_t)(1u << (7u - i));
  36    }
  37    nail_bytes = nails / 8u;
  38
  39    for (i = 0u; i < count; ++i) {
  40       for (j = 0u; j < size; ++j) {
  41          uint8_t *byte = (uint8_t *)rop +
  42                          (((order == MP_LSB_FIRST) ? i : ((count - 1u) - i)) * size) +
  43                          ((endian == MP_LITTLE_ENDIAN) ? j : ((size - 1u) - j));
  44
  45          if (j >= (size - nail_bytes)) {
  46             *byte = 0;
  47             continue;
  48          }
  49
  50          *byte = (uint8_t)((j == ((size - nail_bytes) - 1u)) ? (t.dp[0] & odd_nail_mask) : (t.dp[0] & 0xFFuL));
  51
  52          if ((err = mp_div_2d(&t, (j == ((size - nail_bytes) - 1u)) ? (int)(8u - odd_nails) : 8, &t, NULL)) != MP_OKAY) {
  53             goto LBL_ERR;
  54          }
  55
  56       }
  57    }
  58
  59    if (written != NULL) {
  60       *written = count;
  61    }
  62    err = MP_OKAY;
  63
  64 LBL_ERR:
  65    mp_clear(&t);
  66    return err;
  67 }
  68
  69 #endif