gmp-4.3.1/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 3 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.  If not, see http://www.gnu.org/licenses/.  */

#include <stdio.h>  /* for NULL */
#include "gmp.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;
}