/* Test file for mpfr_sub_ui

Copyright 2000-2025 Free Software Foundation, Inc.
Contributed by the Pascaline and Caramba projects, INRIA.

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 <https://www.gnu.org/licenses/>. */

#include <float.h>

#include "mpfr-test.h"

/* checks that x-y gives the right results with 53 bits of precision */
static void
check3 (const char *xs, unsigned long y, mpfr_rnd_t rnd_mode, const char *zs)
{
  mpfr_t xx,zz;

  mpfr_inits2 (53, xx, zz, (mpfr_ptr) 0);
  mpfr_set_str1 (xx, xs);
  mpfr_sub_ui (zz, xx, y, rnd_mode);
  if (mpfr_cmp_str1(zz, zs))
    {
      printf ("expected sum is %s, got ", zs);
      mpfr_dump (zz);
      printf ("mpfr_sub_ui failed for x=%s y=%lu with rnd_mode=%s\n",
              xs, y, mpfr_print_rnd_mode (rnd_mode));
      exit (1);
    }
  mpfr_clears (xx, zz, (mpfr_ptr) 0);
}

/* FastTwoSum: if EXP(x) >= EXP(y), u = o(x+y), v = o(u-x), w = o(y-v),
               then x + y = u + w
thus if u = o(y-x), v = o(u+x), w = o(v-y), then y-x = u-w */
static void
check_two_sum (mpfr_prec_t p)
{
  unsigned int x;
  mpfr_t y, u, v, w;
  mpfr_rnd_t rnd;
  int inexact;

  mpfr_inits2 (p, y, u, v, w, (mpfr_ptr) 0);
  do
    {
      x = randlimb ();
    }
  while (x < 1);
  mpfr_urandomb (y, RANDS);
  rnd = MPFR_RNDN;
  inexact = mpfr_sub_ui (u, y, x, rnd);
  mpfr_add_ui (v, u, x, rnd);
  mpfr_sub (w, v, y, rnd);
  /* as u - (y-x) = w, we should have inexact and w of same sign */
  if (((inexact == 0) && mpfr_cmp_ui (w, 0)) ||
      ((inexact > 0) && (mpfr_cmp_ui (w, 0) <= 0)) ||
      ((inexact < 0) && (mpfr_cmp_ui (w, 0) >= 0)))
    {
      printf ("Wrong inexact flag for prec=%u, rnd=%s\n",
              (unsigned int) p, mpfr_print_rnd_mode (rnd));
      printf ("x=%u\n", x);
      printf ("y="); mpfr_dump (y);
      printf ("u="); mpfr_dump (u);
      printf ("v="); mpfr_dump (v);
      printf ("w="); mpfr_dump (w);
      printf ("inexact = %d\n", inexact);
      exit (1);
    }
  mpfr_clears (y, u, v, w, (mpfr_ptr) 0);
}

static void
check_nans (void)
{
  mpfr_t  x, y;

  mpfr_init2 (x, 123L);
  mpfr_init2 (y, 123L);

  /* nan - 1 == nan */
  mpfr_set_nan (x);
  mpfr_clear_nanflag ();
  mpfr_sub_ui (y, x, 1L, MPFR_RNDN);
  MPFR_ASSERTN (mpfr_nanflag_p ());
  MPFR_ASSERTN (mpfr_nan_p (y));

  /* +inf - 1 == +inf */
  mpfr_set_inf (x, 1);
  mpfr_sub_ui (y, x, 1L, MPFR_RNDN);
  MPFR_ASSERTN (mpfr_inf_p (y));
  MPFR_ASSERTN (mpfr_sgn (y) > 0);

  /* -inf - 1 == -inf */
  mpfr_set_inf (x, -1);
  mpfr_sub_ui (y, x, 1L, MPFR_RNDN);
  MPFR_ASSERTN (mpfr_inf_p (y));
  MPFR_ASSERTN (mpfr_sgn (y) < 0);

  mpfr_clear (x);
  mpfr_clear (y);
}

#define TEST_FUNCTION mpfr_sub_ui
#define ULONG_ARG2
#define RAND_FUNCTION(x) mpfr_random2(x, MPFR_LIMB_SIZE (x), 1, RANDS)
#include "tgeneric.c"

int
main (int argc, char *argv[])
{
  mpfr_prec_t p;
  int k;

  tests_start_mpfr ();

  check_nans ();

  for (p=2; p<200; p++)
    for (k=0; k<200; k++)
      check_two_sum (p);

  check3 ("0.9999999999", 1, MPFR_RNDN,
          "-10000000827403709990903735160827636718750e-50");

  test_generic (MPFR_PREC_MIN, 1000, 100);

  tests_end_mpfr ();
  return 0;
}
