contrib/mpfr/mul_ui.c

   1 /* mpfr_mul_ui -- multiply a floating-point number by a machine integer
   2    mpfr_mul_si -- multiply a floating-point number by a machine integer
   3
   4 Copyright 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
   5 Contributed by the Arenaire and Cacao projects, INRIA.
   6
   7 This file is part of the GNU MPFR Library.
   8
   9 The GNU MPFR Library is free software; you can redistribute it and/or modify
  10 it under the terms of the GNU Lesser General Public License as published by
  11 the Free Software Foundation; either version 2.1 of the License, or (at your
  12 option) any later version.
  13
  14 The GNU MPFR Library is distributed in the hope that it will be useful, but
  15 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  16 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  17 License for more details.
  18
  19 You should have received a copy of the GNU Lesser General Public License
  20 along with the GNU MPFR Library; see the file COPYING.LIB.  If not, write to
  21 the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,
  22 MA 02110-1301, USA. */
  23
  24 #define MPFR_NEED_LONGLONG_H
  25 #include "mpfr-impl.h"
  26
  27 int
  28 mpfr_mul_ui (mpfr_ptr y, mpfr_srcptr x, unsigned long int u, mp_rnd_t rnd_mode)
  29 {
  30   mp_limb_t *yp;
  31   mp_size_t xn;
  32   int cnt, inexact;
  33   MPFR_TMP_DECL (marker);
  34
  35   if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (x)))
  36     {
  37       if (MPFR_IS_NAN (x))
  38         {
  39           MPFR_SET_NAN (y);
  40           MPFR_RET_NAN;
  41         }
  42       else if (MPFR_IS_INF (x))
  43         {
  44           if (u != 0)
  45             {
  46               MPFR_SET_INF (y);
  47               MPFR_SET_SAME_SIGN (y, x);
  48               MPFR_RET (0); /* infinity is exact */
  49             }
  50           else /* 0 * infinity */
  51             {
  52               MPFR_SET_NAN (y);
  53               MPFR_RET_NAN;
  54             }
  55         }
  56       else /* x is zero */
  57         {
  58           MPFR_ASSERTD (MPFR_IS_ZERO (x));
  59           MPFR_SET_ZERO (y);
  60           MPFR_SET_SAME_SIGN (y, x);
  61           MPFR_RET (0); /* zero is exact */
  62         }
  63     }
  64   else if (MPFR_UNLIKELY (u <= 1))
  65     {
  66       if (u < 1)
  67         {
  68           MPFR_SET_ZERO (y);
  69           MPFR_SET_SAME_SIGN (y, x);
  70           MPFR_RET (0); /* zero is exact */
  71         }
  72       else
  73         return mpfr_set (y, x, rnd_mode);
  74     }
  75   else if (MPFR_UNLIKELY (IS_POW2 (u)))
  76     return mpfr_mul_2si (y, x, MPFR_INT_CEIL_LOG2 (u), rnd_mode);
  77
  78   yp = MPFR_MANT (y);
  79   xn = MPFR_LIMB_SIZE (x);
  80
  81   MPFR_ASSERTD (xn < MP_SIZE_T_MAX);
  82   MPFR_TMP_MARK(marker);
  83   yp = (mp_ptr) MPFR_TMP_ALLOC ((size_t) (xn + 1) * BYTES_PER_MP_LIMB);
  84
  85   MPFR_ASSERTN (u == (mp_limb_t) u);
  86   yp[xn] = mpn_mul_1 (yp, MPFR_MANT (x), xn, u);
  87
  88   /* x * u is stored in yp[xn], ..., yp[0] */
  89
  90   /* since the case u=1 was treated above, we have u >= 2, thus
  91      yp[xn] >= 1 since x was msb-normalized */
  92   MPFR_ASSERTD (yp[xn] != 0);
  93   if (MPFR_LIKELY (MPFR_LIMB_MSB (yp[xn]) == 0))
  94     {
  95       count_leading_zeros (cnt, yp[xn]);
  96       mpn_lshift (yp, yp, xn + 1, cnt);
  97     }
  98   else
  99     {
 100       cnt = 0;
 101     }
 102
 103   /* now yp[xn], ..., yp[0] is msb-normalized too, and has at most
 104      PREC(x) + (BITS_PER_MP_LIMB - cnt) non-zero bits */
 105   MPFR_RNDRAW (inexact, y, yp, (mp_prec_t) (xn + 1) * BITS_PER_MP_LIMB,
 106                rnd_mode, MPFR_SIGN (x), cnt -- );
 107
 108   MPFR_TMP_FREE (marker);
 109
 110   cnt = BITS_PER_MP_LIMB - cnt;
 111   if (MPFR_UNLIKELY (__gmpfr_emax < MPFR_EMAX_MIN + cnt
 112                      || MPFR_GET_EXP (x) > __gmpfr_emax - cnt))
 113     return mpfr_overflow (y, rnd_mode, MPFR_SIGN(x));
 114
 115   MPFR_SET_EXP (y, MPFR_GET_EXP (x) + cnt);
 116   MPFR_SET_SAME_SIGN (y, x);
 117
 118   return inexact;
 119 }
 120
 121 int mpfr_mul_si (mpfr_ptr y, mpfr_srcptr x, long int u, mp_rnd_t rnd_mode)
 122 {
 123   int res;
 124
 125   if (u >= 0)
 126     res = mpfr_mul_ui (y, x, u, rnd_mode);
 127   else
 128     {
 129       res = -mpfr_mul_ui (y, x, -u, MPFR_INVERT_RND (rnd_mode));
 130       MPFR_CHANGE_SIGN (y);
 131     }
 132   return res;
 133 }