* mpz/jacobi.c: Don't retaining old behaviour of mpz_jacobi on even b

	(it wasn't documented in 3.1.1).
	* mpz/jacobi.c, gmp.h (mpz_kronecker, mpz_legendre): Remove separate
	entrypoints, just #define to mpz_jacobi.

The old behaviour of ignoring factors of 2 on b was never documented
and doesn't seem particularly useful, so there's really no need to
keep it, better just make one kronecker style function and share it.

With respect to gmp 3.1.1 we've now got mpz_jacobi fixed to allow
negative b, and mpz_kronecker added.

Could have just told applications mpz_jacobi now has the kronecker
extension, but it matches mpz_kronecker_ui etc better if there's an
mpz_kronecker alias.

__gmpz_jacobi is kept as the primary library entrypoint and
__gmpz_legendre just for compatibility.  Done this way around on the
assumption existing binaries are more likely to be using mpz_jacobi
than mpz_legendre.  Obviously a recompile moves it to the right one if
this is not so.

1 files changed, 26 insertions, 38 deletions

diff --git a/mpz/jacobi.c b/mpz/jacobi.c
index 4998d4f42..76188551d 100644
--- a/mpz/jacobi.c
+++ b/mpz/jacobi.c
@@ -41,11 +41,23 @@ MA 02111-1307, USA. */
   } while (0)
 
 
-/* After some setups this is just a simple binary GCD with the jacobi symbol
-   result tracked during the reduction.
+/* This code does triple duty as mpz_jacobi, mpz_legendre and mpz_kronecker.
+
+   mpz_jacobi could assume b is odd, but the improvements from that seem
+   small compared to other operations, and anything significant should be
+   checked at run-time since we'd like odd b to go fast in mpz_kronecker
+   too.
+
+   mpz_legendre could assume b is an odd prime, but knowing that doesn't
+   present any obvious benefits.  Result 0 wouldn't arise (unless "a" is a
+   multiple of b), but the checking for that takes little time compared to
+   other operations.
+
+   The main loop is just a simple binary GCD with the jacobi symbol result
+   tracked during the reduction.
 
    The special cases for a or b fitting in one limb let mod_1 or modexact_1
-   get used without any copying, and end up just as efficient as the mixed
+   get used, without any copying, and end up just as efficient as the mixed
    precision mpz_kronecker_ui etc.
 
    When tdiv_qr is called it's not necessary to make "a" odd or make a
@@ -76,11 +88,8 @@ Error, error, need BITS_PER_MP_LIMB even
 #endif
 
 
-static int __gmpz_jac_or_kron _PROTO ((REGPARM_2_1 (mpz_srcptr a, mpz_srcptr b, int kronecker))) REGPARM_ATTR (1);
-#define jac_or_kron(a,b,k)  __gmpz_jac_or_kron (REGPARM_2_1 (a,b,k))
-
-static int
-jac_or_kron (mpz_srcptr a, mpz_srcptr b, int kronecker)
+int
+mpz_jacobi (mpz_srcptr a, mpz_srcptr b)
 {
   mp_srcptr  asrcp, bsrcp;
   mp_size_t  asize, bsize;
@@ -108,8 +117,8 @@ jac_or_kron (mpz_srcptr a, mpz_srcptr b, int kronecker)
   if (asize == 0)
     return JACOBI_0LS (blow, bsize);  /* (0/b) */
 
-  /* for mpz_kronecker, (even/even)=0 */
-  if (kronecker && ((alow | blow) & 1) == 0)
+  /* (even/even)=0 */
+  if (((alow | blow) & 1) == 0)
     return 0;
 
   /* account for effect of sign of b, then ignore it */
@@ -137,11 +146,10 @@ jac_or_kron (mpz_srcptr a, mpz_srcptr b, int kronecker)
           
   if (bsize == 1 || (bsize == 2 && (bsecond >> btwos) == 0))
     {
-      /* special case handled with modexact and no copying */
+      /* special case one limb b, use modexact and no copying */
 
-      /* for mpz_kronecker, (a/2)=(2/a) with a odd, and if b is even then a
-         is odd here */
-      result_bit1 ^= kronecker & JACOBI_TWOS_U_BIT1 (btwos, alow);
+      /* (a/2)=(2/a) with a odd, and if b is even then a is odd here */
+      result_bit1 ^= JACOBI_TWOS_U_BIT1 (btwos, alow);
 
       if (blow == 1)   /* (a/1)=1 always */
         return JACOBI_BIT1_TO_PN (result_bit1);
@@ -152,8 +160,8 @@ jac_or_kron (mpz_srcptr a, mpz_srcptr b, int kronecker)
       return mpn_jacobi_base (alow, blow, result_bit1);
     }
 
-  /* Low zero limbs on a can be discarded.  No need to do this for bsize==1,
-     as it's expected to strip anything only very rarely.  */
+  /* Discard low zero limbs of a.  Usually there won't be anything to
+     strip, hence not bothering with it for the bsize==1 case.  */
   MPN_STRIP_LOW_ZEROS_NOT_ZERO (asrcp, asize, alow);
 
   count_trailing_zeros (atwos, alow);
@@ -169,9 +177,8 @@ jac_or_kron (mpz_srcptr a, mpz_srcptr b, int kronecker)
         alow |= asecond << (BITS_PER_MP_LIMB-atwos);
     }
   
-  /* for mpz_kronecker, (a/2)=(2/a) with a odd
-     for mpz_jacobi, ignore btwos */
-  result_bit1 ^= kronecker & JACOBI_TWOS_U_BIT1 (btwos, alow);
+  /* (a/2)=(2/a) with a odd */
+  result_bit1 ^= JACOBI_TWOS_U_BIT1 (btwos, alow);
 
   if (asize == 1 || (asize == 2 && (asecond >> atwos) == 0))
     {
@@ -314,22 +321,3 @@ jac_or_kron (mpz_srcptr a, mpz_srcptr b, int kronecker)
   TMP_FREE (marker);
   return 0;
 }
-
-
-int
-mpz_jacobi (mpz_srcptr a, mpz_srcptr b)
-{
-  return jac_or_kron (a, b, 0);
-}
-
-int
-mpz_legendre (mpz_srcptr a, mpz_srcptr b)
-{
-  return jac_or_kron (a, b, 0);
-}
-
-int
-mpz_kronecker (mpz_srcptr a, mpz_srcptr b)
-{
-  return jac_or_kron (a, b, -1);
-}