mpir/mpq/cmp.c

/* mpq_cmp(u,v) -- Compare U, V.  Return positive, zero, or negative
   based on if U > V, U == V, or U < V.

Copyright 1991, 1994, 1996, 2001, 2002, 2005, 2015 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 "mpir.h"
#include "gmp-impl.h"
#include "longlong.h"

static int
mpq_cmp_numden (mpq_srcptr op1, mpz_srcptr num_op2, mpz_srcptr den_op2)
{
  mp_size_t num1_size = SIZ(NUM(op1));
  mp_size_t den1_size = SIZ(DEN(op1));
  mp_size_t num2_size = SIZ(num_op2);
  mp_size_t den2_size = SIZ(den_op2);
  int op2_is_int;
  mp_limb_t d1h, d2h;
  mp_size_t tmp1_size, tmp2_size;
  mp_ptr tmp1_ptr, tmp2_ptr;
  mp_size_t num1_sign;
  int cc;
  TMP_DECL;

  /* need canonical signs to get right result */
  ASSERT (den1_size > 0);
  ASSERT (den2_size > 0);

  if (num1_size == 0)
    return -num2_size;
  if (num2_size == 0)
    return num1_size;
  if ((num1_size ^ num2_size) < 0) /* I.e. are the signs different? */
    return num1_size;

  num1_sign = num1_size;
  num1_size = ABS (num1_size);

  /* THINK: Does storing d1h and d2h make sense? */
  d1h = PTR(DEN(op1))[den1_size - 1];
  d2h = PTR(den_op2)[den2_size - 1];
  op2_is_int = (den2_size | d2h) == 1;
  if (op2_is_int == (den1_size | d1h)) /* Both ops are integers */
    /* return mpz_cmp (NUM (op1), num_op2); */
    {
      int cmp;

      if (num1_sign != num2_size)
	return num1_sign - num2_size;

      cmp = mpn_cmp (PTR(NUM(op1)), PTR(num_op2), num1_size);
      return (num1_sign > 0 ? cmp : -cmp);
    }

  num2_size = ABS (num2_size);

  tmp1_size = num1_size + den2_size;
  tmp2_size = num2_size + den1_size;

  /* 1. Check to see if we can tell which operand is larger by just looking at
     the number of limbs.  */

  /* NUM1 x DEN2 is either TMP1_SIZE limbs or TMP1_SIZE-1 limbs.
     Same for NUM1 x DEN1 with respect to TMP2_SIZE.  */
  if (tmp1_size > tmp2_size + 1)
    /* NUM1 x DEN2 is surely larger in magnitude than NUM2 x DEN1.  */
    return num1_sign;
  if (tmp2_size + op2_is_int > tmp1_size + 1)
    /* NUM1 x DEN2 is surely smaller in magnitude than NUM2 x DEN1.  */
    return -num1_sign;

  /* 2. Same, but compare the number of significant bits.  */
  {
    int cnt1, cnt2;
    mp_bitcnt_t bits1, bits2;

    count_leading_zeros (cnt1, PTR(NUM(op1))[num1_size - 1]);
    count_leading_zeros (cnt2, d2h);
    bits1 = (mp_bitcnt_t) tmp1_size * GMP_NUMB_BITS - cnt1 - cnt2 + 2 * GMP_NAIL_BITS;

    count_leading_zeros (cnt1, PTR(num_op2)[num2_size - 1]);
    count_leading_zeros (cnt2, d1h);
    bits2 = (mp_bitcnt_t) tmp2_size * GMP_NUMB_BITS - cnt1 - cnt2 + 2 * GMP_NAIL_BITS;

    if (bits1 > bits2 + 1)
      return num1_sign;
    if (bits2 + op2_is_int > bits1 + 1)
      return -num1_sign;
  }

  /* 3. Finally, cross multiply and compare.  */

  TMP_MARK;
  if (op2_is_int)
    {
      tmp2_ptr = TMP_ALLOC_LIMBS (tmp2_size);
      tmp1_ptr = PTR(NUM(op1));
      --tmp1_size;
    }
  else
    {
  TMP_ALLOC_LIMBS_2 (tmp1_ptr,tmp1_size, tmp2_ptr,tmp2_size);

  if (num1_size >= den2_size)
    tmp1_size -= 0 == mpn_mul (tmp1_ptr,
			       PTR(NUM(op1)), num1_size,
			       PTR(den_op2), den2_size);
  else
    tmp1_size -= 0 == mpn_mul (tmp1_ptr,
			       PTR(den_op2), den2_size,
			       PTR(NUM(op1)), num1_size);
    }

   if (num2_size >= den1_size)
     tmp2_size -= 0 == mpn_mul (tmp2_ptr,
				PTR(num_op2), num2_size,
				PTR(DEN(op1)), den1_size);
   else
     tmp2_size -= 0 == mpn_mul (tmp2_ptr,
				PTR(DEN(op1)), den1_size,
				PTR(num_op2), num2_size);


  cc = tmp1_size - tmp2_size != 0
    ? tmp1_size - tmp2_size : mpn_cmp (tmp1_ptr, tmp2_ptr, tmp1_size);
  TMP_FREE;
  return num1_sign < 0 ? -cc : cc;
}

int
mpq_cmp (mpq_srcptr op1, mpq_srcptr op2)
{
  return mpq_cmp_numden (op1, NUM(op2), DEN(op2));
}

int
mpq_cmp_z (mpq_srcptr op1, mpz_srcptr op2)
{
  const static mp_limb_t one = 1;
  const static mpz_t den = MPZ_ROINIT_N ((mp_limb_t *) &one, 1);

  return mpq_cmp_numden (op1, op2, den);
}