tommath/bn_mp_import.c

#include <tommath_private.h>
#ifdef BN_MP_IMPORT_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis
 *
 * LibTomMath is a library that provides multiple-precision
 * integer arithmetic as well as number theoretic functionality.
 *
 * The library was designed directly after the MPI library by
 * Michael Fromberger but has been written from scratch with
 * additional optimizations in place.
 *
 * The library is free for all purposes without any express
 * guarantee it works.
 *
 * Tom St Denis, tstdenis82@gmail.com, http://libtom.org
 */

/* based on gmp's mpz_import.
 * see http://gmplib.org/manual/Integer-Import-and-Export.html
 */
int mp_import(mp_int* rop, size_t count, int order, size_t size,
                            int endian, size_t nails, const void* op) {
   int result;
   size_t odd_nails, nail_bytes, i, j;
   unsigned char odd_nail_mask;

   mp_zero(rop);

   if (endian == 0) {
      union {
         unsigned int i;
         char c[4];
      } lint;
      lint.i = 0x01020304;

      endian = (lint.c[0] == 4) ? -1 : 1;
   }

   odd_nails = (nails % 8);
   odd_nail_mask = 0xff;
   for (i = 0; i < odd_nails; ++i) {
      odd_nail_mask ^= (1 << (7 - i));
   }
   nail_bytes = nails / 8;

   for (i = 0; i < count; ++i) {
      for (j = 0; j < (size - nail_bytes); ++j) {
         unsigned char byte = *(
               (unsigned char*)op +
               (((order == 1) ? i : ((count - 1) - i)) * size) +
               ((endian == 1) ? (j + nail_bytes) : (((size - 1) - j) - nail_bytes))
            );

         if (
            (result = mp_mul_2d(rop, ((j == 0) ? (8 - odd_nails) : 8), rop)) != MP_OKAY) {
            return result;
         }

         rop->dp[0] |= (j == 0) ? (byte & odd_nail_mask) : byte;
         rop->used  += 1;
      }
   }

   mp_clamp(rop);

   return MP_OKAY;
}

#endif

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