New mini-gmp macro GMP_CMP?

[Niels Möller]

I was looking at how to simplify mini-gmp's mpz_cmp_si. I considered
using mpz_cmpabs_ui to handle the case of both inputs negative, which
made it more consice but perhaps not clearer. Then I came up with the
following. 

The pattern (un == 0) ? 0 : u->_mp_d[0] and variants are replaced by
calls to mpz_get_ui which does the same thing, and the pattern (a > b) -
(a < b) is replaced by a GMP_CMP macro.

Resulting context patch below, reducing the code size by a dozen of
lines. Do you think this is also an improvement in clarity?

/Niels

*** /tmp/extdiff.RPnb3V/gmp.afda1bbf3ee3/mini-gmp/mini-gmp.c	2016-11-22 09:18:29.455237339 +0100
--- /home/nisse/hack/gmp/mini-gmp/mini-gmp.c	2016-11-22 08:54:54.290548487 +0100
*************** see https://www.gnu.org/licenses/.  */
*** 70,73 ****
--- 70,75 ----
  #define GMP_MAX(a, b) ((a) > (b) ? (a) : (b))
  
+ #define GMP_CMP(a,b) (((a) > (b)) - ((a) < (b)))
+ 
  #define gmp_assert_nocarry(x) do { \
      mp_limb_t __cy = (x);	   \
*************** int
*** 1778,1784 ****
  mpz_sgn (const mpz_t u)
  {
!   mp_size_t usize = u->_mp_size;
! 
!   return (usize > 0) - (usize < 0);
  }
  
--- 1780,1784 ----
  mpz_sgn (const mpz_t u)
  {
!   return GMP_CMP (u->_mp_size, 0);
  }
  
*************** mpz_cmp_si (const mpz_t u, long v)
*** 1795,1805 ****
      return 1;
    else /* usize == -1 */
!     {
!       mp_limb_t ul = u->_mp_d[0];
!       if ((mp_limb_t)GMP_NEG_CAST (unsigned long int, v) < ul)
! 	return -1;
!       else
! 	return (mp_limb_t)GMP_NEG_CAST (unsigned long int, v) > ul;
!     }
  }
  
--- 1795,1799 ----
      return 1;
    else /* usize == -1 */
!     return GMP_CMP (GMP_NEG_CAST (mp_limb_t, v), u->_mp_d[0]);
  }
  
*************** mpz_cmp_ui (const mpz_t u, unsigned long
*** 1814,1821 ****
      return -1;
    else
!     {
!       mp_limb_t ul = (usize > 0) ? u->_mp_d[0] : 0;
!       return (ul > v) - (ul < v);
!     }
  }
  
--- 1808,1812 ----
      return -1;
    else
!     return GMP_CMP (mpz_get_ui (u), v);
  }
  
*************** int
*** 1837,1849 ****
  mpz_cmpabs_ui (const mpz_t u, unsigned long v)
  {
!   mp_size_t un = GMP_ABS (u->_mp_size);
!   mp_limb_t ul;
! 
!   if (un > 1)
      return 1;
! 
!   ul = (un == 1) ? u->_mp_d[0] : 0;
! 
!   return (ul > v) - (ul < v);
  }
  
--- 1828,1835 ----
  mpz_cmpabs_ui (const mpz_t u, unsigned long v)
  {
!   if (GMP_ABS (u->_mp_size) > 1)
      return 1;
!   else
!     return GMP_CMP (mpz_get_ui (u), v);
  }
  

-- 
Niels Möller. PGP-encrypted email is preferred. Keyid 368C6677.
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