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Diff for /OpenXM_contrib/gmp/mpz/Attic/tstbit.c between version 1.1.1.1 and 1.1.1.2

version 1.1.1.1, 2000/09/09 14:13:00 version 1.1.1.2, 2003/08/25 16:06:34
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 /* mpz_tstbit -- test a specified bit.  Simulate 2's complement representation.  /* mpz_tstbit -- test a specified bit.
   
 Copyright (C) 1997 Free Software Foundation, Inc.  Copyright 2000, 2002 Free Software Foundation, Inc.
   
 This file is part of the GNU MP Library.  This file is part of the GNU MP Library.
   
Line 22  MA 02111-1307, USA. */
Line 22  MA 02111-1307, USA. */
 #include "gmp.h"  #include "gmp.h"
 #include "gmp-impl.h"  #include "gmp-impl.h"
   
   
   /* For negatives the effective twos complement is achieved by negating the
      limb tested, either with a ones or twos complement.  Twos complement
      ("-") is used if there's only zero limbs below the one being tested.
      Ones complement ("~") is used if there's a non-zero below.  Note that "-"
      is correct even if the limb examined is 0 (and the true beginning of twos
      complement is further up).
   
      Testing the limbs below p is unavoidable on negatives, but will usually
      need to examine only *(p-1).  The search is done from *(p-1) down to
      *u_ptr, since that might give better cache locality, and because a
      non-zero limb is perhaps a touch more likely in the middle of a number
      than at the low end.
   
      Bits past the end of available data simply follow sign of u.  Notice that
      the limb_index >= abs_size test covers u=0 too.  */
   
 int  int
 #if __STDC__  mpz_tstbit (mpz_srcptr u, unsigned long bit_index)
 mpz_tstbit (mpz_srcptr d, unsigned long int bit_index)  
 #else  
 mpz_tstbit (d, bit_index)  
      mpz_srcptr d;  
      unsigned long int bit_index;  
 #endif  
 {  {
   mp_size_t dsize = d->_mp_size;    mp_srcptr      u_ptr      = PTR(u);
   mp_ptr dp = d->_mp_d;    mp_size_t      size       = SIZ(u);
   mp_size_t limb_index;    unsigned       abs_size   = ABS(size);
     unsigned long  limb_index = bit_index / GMP_NUMB_BITS;
     mp_srcptr      p          = u_ptr + limb_index;
     mp_limb_t      limb;
   
   limb_index = bit_index / BITS_PER_MP_LIMB;    if (limb_index >= abs_size)
   if (dsize >= 0)      return (size < 0);
   
     limb = *p;
     if (size < 0)
     {      {
       if (limb_index < dsize)        limb = -limb;     /* twos complement */
         return (dp[limb_index] >> (bit_index % BITS_PER_MP_LIMB)) & 1;  
       else  
         /* Testing a bit outside of a positive number.  */  
         return 0;  
     }  
   else  
     {  
       mp_size_t zero_bound;  
   
       dsize = -dsize;        while (p != u_ptr)
           {
       /* Locate the least significant non-zero limb.  */            p--;
       for (zero_bound = 0; dp[zero_bound] == 0; zero_bound++)            if (*p != 0)
         ;              {
                 limb--;   /* make it a ones complement instead */
       if (limb_index > zero_bound)                break;
         {              }
           if (limb_index < dsize)          }
             return (~dp[limb_index] >> (bit_index % BITS_PER_MP_LIMB)) & 1;  
           else  
             /* Testing a bit outside of a negative number.  */  
             return 1;  
         }  
       else if (limb_index == zero_bound)  
         return (-dp[limb_index] >> (bit_index % BITS_PER_MP_LIMB)) & 1;  
       else  
         return 0;  
     }      }
   
     return (limb >> (bit_index % GMP_NUMB_BITS)) & 1;
 }  }
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