[libmath-prime-util-perl] 15/23: Tweak MR test, add environment variables to disable XS and GMP

[Partha P. Mukherjee]

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ppm-guest pushed a commit to annotated tag v0.14
in repository libmath-prime-util-perl.

commit 3e5a8b2eda5466f1126a7039b06ae11947daae1d
Author: Dana Jacobsen <dana at acm.org>
Date:   Wed Nov 28 22:28:21 2012 -0800

    Tweak MR test, add environment variables to disable XS and GMP
---
 Changes                |  3 +++
 TODO                   |  7 +++++--
 factor.c               | 25 ++++++++++++-------------
 lib/Math/Prime/Util.pm |  6 ++++--
 4 files changed, 24 insertions(+), 17 deletions(-)

diff --git a/Changes b/Changes
index 72b964e..86c6544 100644
--- a/Changes
+++ b/Changes
@@ -16,6 +16,9 @@ Revision history for Perl extension Math::Prime::Util.
            jordan_totient          generalization of Euler Totient
            divisor_sum             run coderef for every divisor
 
+    - Allow environment variables MPU_NO_XS and MPU_NO_GMP to turn off XS and
+      GMP support respectively if they are defined and equal to 1.
+
 0.13  19 November 2012
 
     - Fix an issue with prime count, and make prime count available as a
diff --git a/TODO b/TODO
index e317e7f..daade6c 100644
--- a/TODO
+++ b/TODO
@@ -29,8 +29,6 @@
 
 - Make proper pminus1 in PP code, like factor.c.
 
-- Add Lehmer in PP (I have a version, just needs some polishing).
-
 - For bignums, RiemannZeta and RiemmannR are slow and give questionable
   precision.  We should be able to do better.  One problem is the accuracy
   bug in Math::BigFloat.  Perhaps check for Math::MPFR installed and use it?
@@ -47,3 +45,8 @@
    is_provable_prime
    RiemannZeta
    RiemannR
+
+- Add Lehmer in PP (I have a version, just needs some polishing).  This is a
+  high priority, as the test suite now assumes prime_count is fast for large
+  inputs.
+
diff --git a/factor.c b/factor.c
index deedbae..a032cbe 100644
--- a/factor.c
+++ b/factor.c
@@ -142,9 +142,9 @@ static int is_perfect_square(UV n, UV* sqrtn)
  */
 int _XS_miller_rabin(UV n, const UV *bases, int nbases)
 {
-  int b;
-  int s = 0;
+  UV const nm1 = n-1;
   UV d = n-1;
+  int b, r, s = 0;
 
   MPUassert(n > 3, "MR called with n <= 3");
 
@@ -153,15 +153,18 @@ int _XS_miller_rabin(UV n, const UV *bases, int nbases)
     d >>= 1;
   }
   for (b = 0; b < nbases; b++) {
-    int r;
-    UV a = bases[b];
-    UV x;
+    UV x, a = bases[b];
 
     if (a < 2)
       croak("Base %"UVuf" is invalid", a);
 #if 0
     if (a > (n-2))
       croak("Base %"UVuf" is invalid for input %"UVuf, a, n);
+#else
+    if (a >= n)
+      a %= n;
+    if ( (a <= 1) || (a == nm1) )
+      continue;
 #endif
 
     /* n is a strong pseudoprime to this base if either
@@ -170,19 +173,15 @@ int _XS_miller_rabin(UV n, const UV *bases, int nbases)
      */
 
     x = powmod(a, d, n);
-    if ( (x == 1) || (x == (n-1)) )  continue;
+    if ( (x == 1) || (x == nm1) )  continue;
 
     /* cover r = 1 to s-1, r=0 was just done */
     for (r = 1; r < s; r++) {
       x = sqrmod(x, n);
-      if (x == 1) {
-        return 0;
-      } else if (x == (n-1)) {
-        a = 0;
-        break;
-      }
+      if ( x == nm1 )  break;
+      if ( x == 1   )  return 0;
     }
-    if (a != 0)
+    if (r >= s)
       return 0;
   }
   return 1;
diff --git a/lib/Math/Prime/Util.pm b/lib/Math/Prime/Util.pm
index e40c547..0df6425 100644
--- a/lib/Math/Prime/Util.pm
+++ b/lib/Math/Prime/Util.pm
@@ -59,6 +59,7 @@ BEGIN {
   require Math::Prime::Util::PP;  Math::Prime::Util::PP->import();
 
   eval {
+    return 0 if defined $ENV{MPU_NO_XS} && $ENV{MPU_NO_XS} == 1;
     require XSLoader;
     XSLoader::load(__PACKAGE__, $Math::Prime::Util::VERSION);
     prime_precalc(0);
@@ -276,8 +277,9 @@ sub primes {
     } elsif (($high <= (65536*30)) || ($high <= _get_prime_cache_size())) {
       $method = 'Sieve';
 
-    # More memory than we should reasonably use for base sieve?
-    } elsif ($high > (32*1024*1024*30)) {
+    # At some point the segmented sieve is faster than the base sieve, not
+    # to mention using much less memory.
+    } elsif ($high > (1024*1024*30)) {
       $method = 'Segment';
       # The segment sieve doesn't itself use a segmented sieve for the base,
       # so it will slow down for very large endpoints (larger than 10^16).

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