libtommath/mp_unpack.c
2019-10-29 17:40:59 +01:00

50 lines
1.3 KiB
C

#include "tommath_private.h"
#ifdef 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;
uint8_t 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 ^= (uint8_t)(1u << (7u - i));
}
nail_bytes = nails / 8u;
for (i = 0; i < count; ++i) {
for (j = 0; j < (size - nail_bytes); ++j) {
uint8_t byte = *((const uint8_t *)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