[gcc] GCC 4.5.0=>4.5.1

gcc/gmp/mpf/div_2exp.c

-/* mpf_div_2exp -- Divide a float by 2^n.
-
-Copyright 1993, 1994, 1996, 2000, 2001, 2002, 2004 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 "gmp.h"
-#include "gmp-impl.h"
-
-
-/* Multiples of GMP_NUMB_BITS in exp simply mean an amount subtracted from
-   EXP(u) to set EXP(r).  The remainder exp%GMP_NUMB_BITS is then a right
-   shift for the limb data.
-
-   If exp%GMP_NUMB_BITS == 0 then there's no shifting, we effectively just
-   do an mpz_set with changed EXP(r).  Like mpz_set we take prec+1 limbs in
-   this case.  Although just prec would suffice, it's nice to have
-   mpf_div_2exp with exp==0 come out the same as mpz_set.
-
-   When shifting we take up to prec many limbs from the input.  Our shift is
-   cy = mpn_rshift (PTR(r)+1, PTR(u)+k, ...), where k is the number of low
-   limbs dropped from u, and the carry out is stored to PTR(r)[0].  We don't
-   try to work extra bits from PTR(u)[k-1] (when k>=1 makes it available)
-   into that low carry limb.  Just prec limbs (with the high non-zero) from
-   the input is enough bits for the application requested precision, no need
-   to do extra work.
-
-   If r==u the shift will have overlapping operands.  When k>=1 (ie. when
-   usize > prec), the overlap is in the style supported by rshift (ie. dst
-   <= src).
-
-   But when r==u and k==0 (ie. usize <= prec), we would have an invalid
-   overlap (mpn_rshift (rp+1, rp, ...)).  In this case we must instead use
-   mpn_lshift (PTR(r), PTR(u), size, NUMB-shift).  An lshift by NUMB-shift
-   bits gives identical data of course, it's just its overlap restrictions
-   which differ.
-
-   In both shift cases, the resulting data is abs_usize+1 limbs.  "adj" is
-   used to add +1 to that size if the high is non-zero (it may of course
-   have become zero by the shifting).  EXP(u) is the exponent just above
-   those abs_usize+1 limbs, so it gets -1+adj, which means -1 if the high is
-   zero, or no change if the high is non-zero.
-
-   Enhancements:
-
-   The way mpn_lshift is used means successive mpf_div_2exp calls on the
-   same operand will accumulate low zero limbs, until prec+1 limbs is
-   reached.  This is wasteful for subsequent operations.  When abs_usize <=
-   prec, we should test the low exp%GMP_NUMB_BITS many bits of PTR(u)[0],
-   ie. those which would be shifted out by an mpn_rshift.  If they're zero
-   then use that mpn_rshift.  */
-
-void
-mpf_div_2exp (mpf_ptr r, mpf_srcptr u, unsigned long int exp)
-{
-  mp_srcptr up;
-  mp_ptr rp = r->_mp_d;
-  mp_size_t usize;
-  mp_size_t abs_usize;
-  mp_size_t prec = r->_mp_prec;
-  mp_exp_t uexp = u->_mp_exp;
-
-  usize = u->_mp_size;
-
-  if (UNLIKELY (usize == 0))
-    {
-      r->_mp_size = 0;
-      r->_mp_exp = 0;
-      return;
-    }
-
-  abs_usize = ABS (usize);
-  up = u->_mp_d;
-
-  if (exp % GMP_NUMB_BITS == 0)
-    {
-      prec++;                   /* retain more precision here as we don't need
-                                   to account for carry-out here */
-      if (abs_usize > prec)
-        {
-          up += abs_usize - prec;
-          abs_usize = prec;
-        }
-      if (rp != up)
-        MPN_COPY_INCR (rp, up, abs_usize);
-      r->_mp_exp = uexp - exp / GMP_NUMB_BITS;
-    }
-  else
-    {
-      mp_limb_t cy_limb;
-      mp_size_t adj;
-      if (abs_usize > prec)
-        {
-          up += abs_usize - prec;
-          abs_usize = prec;
-          /* Use mpn_rshift since mpn_lshift operates downwards, and we
-             therefore would clobber part of U before using that part, in case
-             R is the same variable as U.  */
-          cy_limb = mpn_rshift (rp + 1, up, abs_usize, exp % GMP_NUMB_BITS);
-          rp[0] = cy_limb;
-          adj = rp[abs_usize] != 0;
-        }
-      else
-        {
-          cy_limb = mpn_lshift (rp, up, abs_usize,
-                                GMP_NUMB_BITS - exp % GMP_NUMB_BITS);
-          rp[abs_usize] = cy_limb;
-          adj = cy_limb != 0;
-        }
-
-      abs_usize += adj;
-      r->_mp_exp = uexp - exp / GMP_NUMB_BITS - 1 + adj;
-    }
-  r->_mp_size = usize >= 0 ? abs_usize : -abs_usize;
-}