path: root/src/fpif.c

/* mpfr_fpif -- Binary export & import of MPFR numbers
   (floating-point interchange format)

Copyright 2012-2017 Free Software Foundation, Inc.
Contributed by Olivier Demengeon.

This file is part of the GNU MPFR Library.

The GNU MPFR 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 MPFR 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 MPFR Library; see the file COPYING.LESSER.  If not, see
http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */

#define MPFR_USE_FILE
#include "mpfr-impl.h"

#if !defined (HAVE_BIG_ENDIAN) && !defined (HAVE_LITTLE_ENDIAN)
#error "Endianness is unknown. Not supported yet."
#endif

/* The format is described as follows. Any multi-byte number is encoded
   in little endian.

   1. We first store the precision p (this format is able to represent
      any precision from 1 to 2^64 + 248).
      Let B be the first byte (0 <= B <= 255).
        * If B >= 8, the precision p is B-7.
          Here, the condition is equivalent to 1 <= p <= 248.
        * If B <= 7, the next B+1 bytes contain p-249.
          Here, the condition is equivalent to 249 <= p <= 2^64 + 248.
      We will use the following macros:
        * MPFR_MAX_PRECSIZE = 7
        * MPFR_MAX_EMBEDDED_PRECISION = 255 - 7 = 248

   2. Then we store the sign bit and exponent related information
      (possibly a special value). We first have byte A = [seeeeeee],
      where s is the sign bit and E = [eeeeeee] such that:
        * If 0 <= E <= 94, then the exponent e is E-47 (-47 <= e <= 47).
        * If 95 <= E <= 110, the exponent is stored in the next E-94 bytes
          (1 to 16 bytes) in sign + absolute value representation.
        * If 111 <= E <= 118, the exponent size S is stored in the next
          E-110 bytes (1 to 8), then the exponent itself is stored in the
          next S bytes. [Not implemented yet]
        * If 119 <= E <= 127, we have a special value:
          E = 119 (MPFR_KIND_ZERO) for a signed zero;
          E = 120 (MPFR_KIND_INF) for a signed infinity;
          E = 121 (MPFR_KIND_NAN) for NaN.
          *** FIXME *** Decide whether the sign bit of NaN matters here
          (the sign is currently transmitted before checking the value,
          so that the code would not need to be changed).
          It seems important that for export, the sign bit of NaN be
          specified in some way (to ease things like binary diffs or
          hashes).

   3. Then we store the significand (for regular values).

   Note: When a size is stored, it must be minimal, i.e. a number cannot
   start with a null byte. Otherwise the import may fail.
*/

#define MPFR_MAX_PRECSIZE 7
#define MPFR_MAX_EMBEDDED_PRECISION (255 - MPFR_MAX_PRECSIZE)

#define MPFR_KIND_ZERO 119
#define MPFR_KIND_INF 120
#define MPFR_KIND_NAN 121
#define MPFR_MAX_EMBEDDED_EXPONENT 47
#define MPFR_EXTERNAL_EXPONENT 94

/* Begin: Low level helper functions */

/* storage must have an unsigned type */
#define COUNT_NB_BYTE(storage, size)            \
  do                                            \
    {                                           \
      (storage) >>= 8;                          \
      (size)++;                                 \
    }                                           \
  while ((storage) != 0)

#define ALLOC_RESULT(buffer, buffer_size, wanted_size)                  \
  do                                                                    \
    {                                                                   \
      if ((buffer) == NULL || *(buffer_size) < (wanted_size))           \
        {                                                               \
          (buffer) = (unsigned char *) mpfr_reallocate_func             \
            ((buffer), *(buffer_size), (wanted_size));                  \
          if ((buffer) == NULL)                                         \
            {                                                           \
              *(buffer_size) = 0;                                       \
              return NULL;                                              \
            }                                                           \
        }                                                               \
      *(buffer_size) = (wanted_size);                                   \
    }                                                                   \
  while (0)

/*
 * size in byte of a MPFR number in a binary object of a variable size
 */
#define MAX_VARIABLE_STORAGE(exponent_size, precision) \
  ((size_t)(((precision) >> 3) + (exponent_size) +     \
            ((precision) > 248 ? sizeof(mpfr_prec_t) : 0) + 3))

/* copy in result[] the values in data[] with a different endianness,
   where data_size might be smaller than data_max_size, so that we only
   copy data_size bytes from the end of data[]. */
static void
#if defined (HAVE_BIG_ENDIAN)
putLittleEndianData (unsigned char *result, unsigned char *data,
                     size_t data_max_size, size_t data_size)
#elif defined (HAVE_LITTLE_ENDIAN)
putBigEndianData (unsigned char *result, unsigned char *data,
                  size_t data_max_size, size_t data_size)
#endif
{
  size_t j;

  MPFR_ASSERTD (data_size <= data_max_size);
  for (j = 0; j < data_size; j++)
    result[j] = data[data_max_size - j - 1];
}

/* copy in result[] the values in data[] with the same endianness */
static void
#if defined (HAVE_BIG_ENDIAN)
putBigEndianData (unsigned char *result, unsigned char *data,
                  size_t data_max_size, size_t data_size)
#elif defined (HAVE_LITTLE_ENDIAN)
putLittleEndianData (unsigned char *result, unsigned char *data,
                     size_t data_max_size, size_t data_size)
#endif
{
  MPFR_ASSERTD (data_size <= data_max_size);
  memcpy (result, data, data_size);
}

/* copy in result[] the values in data[] with a different endianness;
   the data are written at the end of the result[] buffer (if
   data_size < data_max_size, the first bytes of result[] are
   left untouched). */
static void
#if defined (HAVE_BIG_ENDIAN)
getLittleEndianData (unsigned char *result, unsigned char *data,
                     size_t data_max_size, size_t data_size)
#elif defined (HAVE_LITTLE_ENDIAN)
getBigEndianData (unsigned char *result, unsigned char *data,
                  size_t data_max_size, size_t data_size)
#endif
{
  size_t j;

  MPFR_ASSERTD (data_size <= data_max_size);
  for (j = 0; j < data_size; j++)
    result[data_max_size - j - 1] = data[j];
}

/* copy in result[] the values in data[] with the same endianness */
static void
#if defined (HAVE_BIG_ENDIAN)
getBigEndianData (unsigned char *result, unsigned char *data,
                  size_t data_max_size, size_t data_size)
#elif defined (HAVE_LITTLE_ENDIAN)
getLittleEndianData (unsigned char *result, unsigned char *data,
                     size_t data_max_size, size_t data_size)
#endif
{
  MPFR_ASSERTD (data_size <= data_max_size);
  memcpy (result, data, data_size);
}

/* End: Low level helper functions */

/* Internal Function */
/*
 * buffer : OUT : store the precision in binary format, can be null
 *               (may be reallocated if too small)
 * buffer_size : IN/OUT : size of the buffer => size used in the buffer
 * precision : IN : precision to store
 * return pointer to a buffer storing the precision in binary format
 */
static unsigned char *
mpfr_fpif_store_precision (unsigned char *buffer, size_t *buffer_size,
                           mpfr_prec_t precision)
{
  unsigned char *result;
  size_t size_precision;

  MPFR_ASSERTD (precision >= 1);
  size_precision = 0;

  if (precision > MPFR_MAX_EMBEDDED_PRECISION)
    {
      mpfr_uprec_t copy_precision;

      copy_precision = precision - (MPFR_MAX_EMBEDDED_PRECISION + 1);
      COUNT_NB_BYTE(copy_precision, size_precision);
    }

  result = buffer;
  ALLOC_RESULT(result, buffer_size, size_precision + 1);

  if (precision > MPFR_MAX_EMBEDDED_PRECISION)
    {
      result[0] = size_precision - 1;
      precision -= (MPFR_MAX_EMBEDDED_PRECISION + 1);
      putLittleEndianData (result + 1, (unsigned char *) &precision,
                           sizeof(mpfr_prec_t), size_precision);
    }
  else
    result[0] = precision + MPFR_MAX_PRECSIZE;

  return result;
}

#define BUFFER_SIZE 8

/*
 * fh : IN : file handler
 * return the precision stored in the binary buffer, 0 in case of error
 */
static mpfr_prec_t
mpfr_fpif_read_precision_from_file (FILE *fh)
{
  mpfr_prec_t precision;
  size_t precision_size;
  unsigned char buffer[BUFFER_SIZE];

  if (fh == NULL)
    return 0;

  if (fread (buffer, 1, 1, fh) != 1)
    return 0;

  precision_size = buffer[0];
  if (precision_size > MPFR_MAX_PRECSIZE)
    return precision_size - MPFR_MAX_PRECSIZE;

  precision_size++;
  MPFR_ASSERTD (precision_size <= BUFFER_SIZE);

  /* Read the precision in little-endian format. */
  if (fread (buffer, precision_size, 1, fh) != 1)
    return 0;

  while (precision_size > sizeof(mpfr_prec_t))
    {
      if (buffer[precision_size-1] != 0)
        return 0;  /* the read precision doesn't fit in a mpfr_prec_t */
      precision_size--;
    }

  if (precision_size == sizeof(mpfr_prec_t) &&
      buffer[precision_size-1] >= 0x80)
    return 0;  /* the read precision doesn't fit in a mpfr_prec_t */

  precision = 0;  /* to pad with 0's if data_size < data_max_size */

  /* On big-endian machines, the data must be copied at the end of the
     precision object in the memory; thus data_max_size (3rd argument)
     must be sizeof(mpfr_prec_t). */
  getLittleEndianData ((unsigned char *) &precision, buffer,
                       sizeof(mpfr_prec_t), precision_size);

  return precision + (MPFR_MAX_EMBEDDED_PRECISION + 1);
}

/*
 * buffer : OUT : store the kind of the MPFR number x, its sign, the size of
 *                its exponent and its exponent value in a binary format,
 *                can be null (may be reallocated if too small)
 * buffer_size : IN/OUT : size of the buffer => size used in the buffer
 * x : IN : MPFR number
 * return pointer to a buffer storing the kind of the MPFR number x, its sign,
 *        the size of its exponent and its exponent value in a binary format,
 */
/* TODO
 *   Exponents that use more than 16 bytes are not managed (not an issue
 *   until one has integer types larger than 128 bits).
 */
static unsigned char*
mpfr_fpif_store_exponent (unsigned char *buffer, size_t *buffer_size, mpfr_t x)
{
  unsigned char *result;
  mpfr_uexp_t uexp;
  size_t exponent_size;

  exponent_size = 0;

  if (MPFR_IS_PURE_FP (x))
    {
      mpfr_exp_t exponent = MPFR_GET_EXP (x);

      if (exponent > MPFR_MAX_EMBEDDED_EXPONENT ||
          exponent < -MPFR_MAX_EMBEDDED_EXPONENT)
        {
          mpfr_uexp_t copy_exponent, exp_sign_bit;

          uexp = SAFE_ABS (mpfr_uexp_t, exponent)
            - MPFR_MAX_EMBEDDED_EXPONENT;

          /* Shift uexp to take the sign bit of the exponent into account.
             Because of constraints on the valid exponents, this cannot
             overflow (check with an MPFR_ASSERTD). */
          copy_exponent = uexp << 1;
          MPFR_ASSERTD (copy_exponent > uexp);
          COUNT_NB_BYTE(copy_exponent, exponent_size);
          MPFR_ASSERTN (exponent_size <= 16);  /* see TODO */

          /* Sign bit of the exponent. */
          exp_sign_bit = (mpfr_uexp_t) 1 << (8 * exponent_size - 1);
          MPFR_ASSERTD (uexp < exp_sign_bit);
          if (exponent < 0)
            uexp |= exp_sign_bit;
        }
      else
        uexp = exponent + MPFR_MAX_EMBEDDED_EXPONENT;
    }

  result = buffer;
  ALLOC_RESULT(result, buffer_size, exponent_size + 1);

  if (MPFR_IS_PURE_FP (x))
    {
      if (exponent_size == 0)
        result[0] = uexp;
      else
        {
          result[0] = MPFR_EXTERNAL_EXPONENT + exponent_size;

          putLittleEndianData (result + 1, (unsigned char *) &uexp,
                               sizeof(mpfr_exp_t), exponent_size);
        }
    }
  else if (MPFR_IS_ZERO (x))
    result[0] = MPFR_KIND_ZERO;
  else if (MPFR_IS_INF (x))
    result[0] = MPFR_KIND_INF;
  else
    {
      MPFR_ASSERTD (MPFR_IS_NAN (x));
      result[0] = MPFR_KIND_NAN;
    }

  /* Set the sign, even for NaN. */
  if (MPFR_IS_NEG (x))
    result[0] |= 0x80;

  return result;
}

/*
 * x : OUT : MPFR number extracted from the binary buffer
 * fh : IN : file handler
 * return 0 if successful
 */
/* TODO
 *   Exponents that use more than 16 bytes are not managed (this is not
 *   an issue if the data were written by MPFR with mpfr_exp_t not larger
 *   than 128 bits).
 */
static int
mpfr_fpif_read_exponent_from_file (mpfr_t x, FILE * fh)
{
  mpfr_exp_t exponent;
  mpfr_uexp_t uexp;
  size_t exponent_size;
  int sign;
  unsigned char buffer[sizeof(mpfr_exp_t)];

  if (fh == NULL)
    return 1;

  if (fread (buffer, 1, 1, fh) != 1)
    return 1;

  /* sign value that can be used with MPFR_SET_SIGN,
     mpfr_set_zero and mpfr_set_inf */
  sign = (buffer[0] & 0x80) ? MPFR_SIGN_NEG : MPFR_SIGN_POS;
  /* Set the sign, even for NaN. */
  MPFR_SET_SIGN (x, sign);

  exponent = buffer[0] & 0x7F;
  exponent_size = 1;

  if (exponent > MPFR_EXTERNAL_EXPONENT && exponent < MPFR_KIND_ZERO)
    {
      mpfr_uexp_t exp_sign_bit;

      exponent_size = exponent - MPFR_EXTERNAL_EXPONENT;

      /* A failure is acceptable when the exponent starts with leading zeros,
         even if it would fit in mpfr_exp_t (see format description). */
      if (MPFR_UNLIKELY (exponent_size > 16 /* see TODO */ ||
                         exponent_size > sizeof(mpfr_exp_t)))
        return 1;

      if (MPFR_UNLIKELY (fread (buffer, exponent_size, 1, fh) != 1))
        return 1;

      uexp = 0;
      getLittleEndianData ((unsigned char *) &uexp, buffer,
                           sizeof(mpfr_exp_t), exponent_size);

      /* Sign bit of the exponent. */
      exp_sign_bit = uexp & ((mpfr_uexp_t) 1 << (8 * exponent_size - 1));

      uexp &= ~exp_sign_bit;
      uexp += MPFR_MAX_EMBEDDED_EXPONENT;
      if (MPFR_UNLIKELY (uexp > MPFR_EMAX_MAX && uexp > -MPFR_EMIN_MIN))
        return 1;

      exponent = exp_sign_bit ? - (mpfr_exp_t) uexp : (mpfr_exp_t) uexp;
      if (MPFR_UNLIKELY (! MPFR_EXP_IN_RANGE (exponent)))
        return 1;
      MPFR_SET_EXP (x, exponent);

      exponent_size++;
    }
  else if (exponent == MPFR_KIND_ZERO)
    MPFR_SET_ZERO (x);
  else if (exponent == MPFR_KIND_INF)
    MPFR_SET_INF (x);
  else if (exponent == MPFR_KIND_NAN)
    MPFR_SET_NAN (x);
  else if (exponent <= MPFR_EXTERNAL_EXPONENT)
    {
      exponent -= MPFR_MAX_EMBEDDED_EXPONENT;
      if (MPFR_UNLIKELY (! MPFR_EXP_IN_RANGE (exponent)))
        return 1;
      MPFR_SET_EXP (x, exponent);
    }
  else
    return 1;

  return 0;
}

/*
 * buffer : OUT : store the limb of the MPFR number x in a binary format,
 *                can be null (may be reallocated if too small)
 * buffer_size : IN/OUT : size of the buffer => size used in the buffer
 * x : IN : MPFR number
 * return pointer to a buffer storing the limb of the MPFR number x in a binary
 *        format
 */
static unsigned char*
mpfr_fpif_store_limbs (unsigned char *buffer, size_t *buffer_size, mpfr_t x)
{
  unsigned char *result;
  mpfr_prec_t precision;
  size_t nb_byte;
  size_t nb_limb, mp_bytes_per_limb;
  size_t nb_partial_byte;
  size_t i, j;

  precision = mpfr_get_prec (x);
  nb_byte = (precision + 7) >> 3;
  mp_bytes_per_limb = mp_bits_per_limb >> 3;
  nb_partial_byte = nb_byte % mp_bytes_per_limb;
  nb_limb = (nb_byte + mp_bytes_per_limb - 1) / mp_bytes_per_limb;

  result = buffer;
  ALLOC_RESULT(result, buffer_size, nb_byte);

  putBigEndianData (result, (unsigned char*) MPFR_MANT(x),
                    sizeof(mp_limb_t), nb_partial_byte);
  for (i = nb_partial_byte, j = (nb_partial_byte == 0) ? 0 : 1; j < nb_limb;
       i += mp_bytes_per_limb, j++)
    putLittleEndianData (result + i, (unsigned char*) (MPFR_MANT(x) + j),
                         sizeof(mp_limb_t), sizeof(mp_limb_t));

  return result;
}

/*
 * x : OUT : MPFR number extracted from the binary buffer, should have the same
 *           precision than the number in the binary format
 * buffer : IN : limb of the MPFR number x in a binary format,
 * buffer_size : IN/OUT : size of the buffer => size used in the buffer
 * return 0 if successful
 */
static int
mpfr_fpif_read_limbs (mpfr_t x, unsigned char *buffer, size_t *buffer_size)
{
  mpfr_prec_t precision;
  size_t nb_byte;
  size_t mp_bytes_per_limb;
  size_t nb_partial_byte;
  size_t i, j;

  precision = mpfr_get_prec (x);
  nb_byte = (precision + 7) >> 3;
  mp_bytes_per_limb = mp_bits_per_limb >> 3;
  nb_partial_byte = nb_byte % mp_bytes_per_limb;

  if ((buffer == NULL) || (*buffer_size < nb_byte))
    {
      *buffer_size = 0;
      return 1;
    }
  *buffer_size = nb_byte;

  if (nb_partial_byte > 0)
    {
      memset (MPFR_MANT(x), 0, sizeof(mp_limb_t));
      getBigEndianData ((unsigned char*) MPFR_MANT(x), buffer,
                        sizeof(mp_limb_t), nb_partial_byte);
    }
  for (i = nb_partial_byte, j = (nb_partial_byte == 0) ? 0 : 1; i < nb_byte;
       i += mp_bytes_per_limb, j++)
    getLittleEndianData ((unsigned char*) (MPFR_MANT(x) + j), buffer + i,
                         sizeof(mp_limb_t), sizeof(mp_limb_t));

  return 0;
}

/* External Function */
/*
 * fh : IN : file hander
 * x : IN : MPFR number to put in the file
 * return 0 if successful
 */
int
mpfr_fpif_export (FILE *fh, mpfr_t x)
{
  int status;
  unsigned char *buf;
  unsigned char *bufResult;
  size_t used_size, buf_size;

  if (fh == NULL)
    return -1;

  buf_size = MAX_VARIABLE_STORAGE(sizeof(mpfr_exp_t), mpfr_get_prec (x));
  buf = (unsigned char*) mpfr_allocate_func (buf_size);
  if (buf == NULL)
    return -1;

  used_size = buf_size;
  buf = mpfr_fpif_store_precision (buf, &used_size, mpfr_get_prec (x));
  used_size > buf_size ? buf_size = used_size : 0;
  status = fwrite (buf, used_size, 1, fh);
  if (status != 1)
    {
      mpfr_free_func (buf, buf_size);
      return -1;
    }
  used_size = buf_size;
  bufResult = mpfr_fpif_store_exponent (buf, &used_size, x);
  if (bufResult == NULL)
    {
      mpfr_free_func (buf, buf_size);
      return -1;
    }
  buf = bufResult;
  used_size > buf_size ? buf_size = used_size : 0;
  status = fwrite (buf, used_size, 1, fh);
  if (status != 1)
    {
      mpfr_free_func (buf, buf_size);
      return -1;
    }

  if (mpfr_regular_p (x))
    {
      used_size = buf_size;
      buf = mpfr_fpif_store_limbs (buf, &used_size, x);
      used_size > buf_size ? buf_size = used_size : 0;
      status = fwrite (buf, used_size, 1, fh);
      if (status != 1)
        {
          mpfr_free_func (buf, buf_size);
          return -1;
        }
    }

  mpfr_free_func (buf, buf_size);
  return 0;
}

/*
 * x : IN/OUT : MPFR number extracted from the file, its precision is reset to
 *              be able to hold the number
 * fh : IN : file hander
 * Return 0 if the import was successful.
 */
int
mpfr_fpif_import (mpfr_t x, FILE *fh)
{
  int status;
  mpfr_prec_t precision;
  unsigned char *buffer;
  size_t used_size;

  precision = mpfr_fpif_read_precision_from_file (fh);
  if (precision == 0) /* precision = 0 means an error */
    return -1;
  if (precision > MPFR_PREC_MAX)
    return -1;
  MPFR_STAT_STATIC_ASSERT (MPFR_PREC_MIN == 1);  /* as specified */
  mpfr_set_prec (x, precision);

  status = mpfr_fpif_read_exponent_from_file (x, fh);
  if (status != 0)
    {
      mpfr_set_nan (x);
      return -1;
    }

  /* Warning! The significand of x is not set yet. Thus use MPFR_IS_SINGULAR
     for the test. */
  if (!MPFR_IS_SINGULAR (x))
    {
      /* For portability, we need to consider bytes with only 8 significant
         bits in the interchange format. That's OK because CHAR_BIT >= 8.
         But the implementation is currently not clear when CHAR_BIT > 8.
         This may have never been tested. For safety, require CHAR_BIT == 8,
         and test/adapt the code if this ever fails. */
      MPFR_STAT_STATIC_ASSERT (CHAR_BIT == 8);
      MPFR_STAT_STATIC_ASSERT ((MPFR_PREC_MAX + 7) >> 3 <= (size_t) -1);
      used_size = (precision + 7) >> 3; /* ceil(precision/8) */
      buffer = (unsigned char*) mpfr_allocate_func (used_size);
      if (buffer == NULL)
        {
          mpfr_set_nan (x);
          return -1;
        }
      status = fread (buffer, used_size, 1, fh);
      if (status != 1)
        {
          mpfr_free_func (buffer, used_size);
          mpfr_set_nan (x);
          return -1;
        }
      status = mpfr_fpif_read_limbs (x, buffer, &used_size);
      mpfr_free_func (buffer, used_size);
      if (status != 0)
        {
          mpfr_set_nan (x);
          return -1;
        }
    }

  return 0;
}