mpir/mpz/export.c

/* mpz_export -- create word data from mpz.

Copyright 2002, 2003 Free Software Foundation, Inc.

This file is part of the GNU MP Library.

The GNU MP Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or (at your
option) any later version.

The GNU MP Library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
License for more details.

You should have received a copy of the GNU Lesser General Public License
along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
MA 02110-1301, USA. */

#include <stdio.h>  /* for NULL */
#include "mpir.h"
#include "gmp-impl.h"
#include "longlong.h"


#if HAVE_LIMB_BIG_ENDIAN
#define HOST_ENDIAN     1
#endif
#if HAVE_LIMB_LITTLE_ENDIAN
#define HOST_ENDIAN     (-1)
#endif
#ifndef HOST_ENDIAN
static const mp_limb_t  endian_test = (CNST_LIMB(1) << (GMP_LIMB_BITS-7)) - 1;
#define HOST_ENDIAN     (* (signed char *) &endian_test)
#endif


#define MPN_SIZEINBASE_2EXP(result, ptr, size, base2exp)                \
  do {                                                                  \
    int            __cnt;                                               \
    unsigned long  __totbits;                                           \
    ASSERT ((size) > 0);                                                \
    ASSERT ((ptr)[(size)-1] != 0);                                      \
    count_leading_zeros (__cnt, (ptr)[(size)-1]);                       \
    __totbits = (size) * GMP_NUMB_BITS - (__cnt - GMP_NAIL_BITS);       \
    (result) = (__totbits + (base2exp)-1) / (base2exp);                 \
  } while (0)


void *
mpz_export (void *data, size_t *countp, int order,
            size_t size, int endian, size_t nail, mpz_srcptr z)
{
  mp_size_t      zsize;
  mp_srcptr      zp;
  size_t         count, dummy;
  unsigned long  numb;
  unsigned       align;

  ASSERT (order == 1 || order == -1);
  ASSERT (endian == 1 || endian == 0 || endian == -1);
  ASSERT (nail <= 8*size);
  ASSERT (8*size-nail > 0);

  if (countp == NULL)
    countp = &dummy;

  zsize = SIZ(z);
  if (zsize == 0)
    {
      *countp = 0;
      return data;
    }

  zsize = ABS (zsize);
  zp = PTR(z);
  numb = 8*size - nail;
  MPN_SIZEINBASE_2EXP (count, zp, zsize, numb);
  *countp = count;

  if (data == NULL)
    data = (*__gmp_allocate_func) (count*size);

  if (endian == 0)
    endian = HOST_ENDIAN;

  align = ((char *) data - (char *) NULL) % sizeof (mp_limb_t);

  if (nail == GMP_NAIL_BITS)
    {
      if (size == sizeof (mp_limb_t) && align == 0)
        {
          if (order == -1 && endian == HOST_ENDIAN)
            {
              MPN_COPY ((mp_ptr) data, zp, (mp_size_t) count);
              return data;
            }
          if (order == 1 && endian == HOST_ENDIAN)
            {
              MPN_REVERSE ((mp_ptr) data, zp, (mp_size_t) count);
              return data;
            }

          if (order == -1 && endian == -HOST_ENDIAN)
            {
              MPN_BSWAP ((mp_ptr) data, zp, (mp_size_t) count);
              return data;
            }
          if (order == 1 && endian == -HOST_ENDIAN)
            {
              MPN_BSWAP_REVERSE ((mp_ptr) data, zp, (mp_size_t) count);
              return data;
            }
        }
    }

  {
    mp_limb_t      limb, wbitsmask;
    size_t         i, numb;
    mp_size_t      j, wbytes, woffset;
    unsigned char  *dp;
    int            lbits, wbits;
    mp_srcptr      zend;

    numb = size * 8 - nail;

    /* whole bytes per word */
    wbytes = numb / 8;

    /* possible partial byte */
    wbits = numb % 8;
    wbitsmask = (CNST_LIMB(1) << wbits) - 1;

    /* offset to get to the next word */
    woffset = (endian >= 0 ? size : - (mp_size_t) size)
      + (order < 0 ? size : - (mp_size_t) size);

    /* least significant byte */
    dp = (unsigned char *) data
      + (order >= 0 ? (count-1)*size : 0) + (endian >= 0 ? size-1 : 0);

#define EXTRACT(N, MASK)                                \
    do {                                                \
      if (lbits >= (N))                                 \
        {                                               \
          *dp = limb MASK;                              \
          limb >>= (N);                                 \
          lbits -= (N);                                 \
        }                                               \
      else                                              \
        {                                               \
          mp_limb_t  newlimb;                           \
          newlimb = (zp == zend ? 0 : *zp++);           \
          *dp = (limb | (newlimb << lbits)) MASK;       \
          limb = newlimb >> ((N)-lbits);                \
          lbits += GMP_NUMB_BITS - (N);                 \
        }                                               \
    } while (0)

    zend = zp + zsize;
    lbits = 0;
    limb = 0;
    for (i = 0; i < count; i++)
      {
        for (j = 0; j < wbytes; j++)
          {
            EXTRACT (8, + 0);
            dp -= endian;
          }
        if (wbits != 0)
          {
            EXTRACT (wbits, & wbitsmask);
            dp -= endian;
            j++;
          }
        for ( ; j < size; j++)
          {
            *dp = '\0';
            dp -= endian;
          }
        dp += woffset;
      }

    ASSERT (zp == PTR(z) + ABSIZ(z));

    /* low byte of word after most significant */
    ASSERT (dp == (unsigned char *) data
            + (order < 0 ? count*size : - (mp_size_t) size)
            + (endian >= 0 ? (mp_size_t) size - 1 : 0));
  }
  return data;
}