Re: Please test pari-2.5.1 prerelease 2

[Bill Allombert <Bill.Allombert@math.u-bordeaux1.fr>]

On Fri, Feb 10, 2012 at 09:34:52PM +0100, Bill Allombert wrote:
> On Fri, Feb 10, 2012 at 07:37:02PM +0100, Leonardo Cangelmi wrote:
> > 
> > I tested pari-2.5.1 (the prerelease 2 and then the stable version). There
> > are no problems in compilation and tests. However, the total time taken by
> > test-all is longer than in version 2.5.0 (see the attached bench files).
> 
> Thanks for your careful tests!
> 
> Note that when we fix a bug in 2.5.1, we generally add a new test, so it is
> expected that the new testsuite takes more time. However, in this case the
> difference is large and is indeed a regression.
> 
> The largest slowdown is in test-resultant. It was introduced by
> the commit 5301c466d2 which fixes this bug:
>     18- subst(Y/X,X,x) -> 0
> 
> We will try to address that in 2.5.2.

I found out that the unstable branch is not affected due to the second half of
961d38a24ef improving substvec speed tremendously. Unfortunately I only applied
the first half to PARI 2.5.1 (since the second half is not a bug fix).

Please find a patch which apply the second half, which I am considering to apply
to 2.5.2.

Cheers,
Bill.

>From c325dedd4d680dd95a6e8622d4d69c04135f40c2 Mon Sep 17 00:00:00 2001
From: Karim Belabas <Karim.Belabas@math.u-bordeaux1.fr>
Date: Tue, 23 Aug 2011 13:19:27 +0000
Subject: [PATCH] improve substvec speed.

---
 src/basemath/gen3.c |   27 ++++++++++++++++-----------
 1 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/src/basemath/gen3.c b/src/basemath/gen3.c
index 4f86849..5673bc1 100644
--- a/src/basemath/gen3.c
+++ b/src/basemath/gen3.c
@@ -1453,24 +1453,29 @@ GEN
 gsubstvec(GEN e, GEN v, GEN r)
 {
   pari_sp ltop=avma;
-  long i,l=lg(v);
+  long i, j, l = lg(v);
   GEN w,z;
-  if ( !is_vec_t(typ(v)) || !is_vec_t(typ(r)) )
-    pari_err(typeer,"substvec");
+  if ( !is_vec_t(typ(v)) || !is_vec_t(typ(r)) ) pari_err(typeer,"substvec");
   if (lg(r)!=l)
     pari_err(talker,"different number of variables and values in substvec");
-  w=cgetg(l,t_VECSMALL);
-  z=cgetg(l,t_VECSMALL);
-  for(i=1;i<l;i++)
+  w = cgetg(l,t_VECSMALL);
+  z = cgetg(l,t_VECSMALL);
+  for(i=j=1;i<l;i++)
   {
     GEN T = gel(v,i);
     if (!gcmpX(T)) pari_err(talker,"not a variable in substvec (%Ps)", T);
-    w[i]=varn(T);
-    z[i]=fetch_var();
+    if (gvar(gel(r,i)) == NO_VARIABLE) /* no need to take precautions */
+      e = gsubst(e, varn(T), gel(r,i));
+    else
+    {
+      w[j]=varn(T);
+      z[j]=fetch_var();
+      j++;
+    }
   }
-  for(i=1;i<l;i++) e = gsubst(e,w[i],pol_x(z[i]));
-  for(i=1;i<l;i++) e = gsubst(e,z[i],gel(r,i));
-  for(i=1;i<l;i++) (void)delete_var();
+  for(i=1;i<j;i++) e = gsubst(e,w[i],pol_x(z[i]));
+  for(i=1;i<j;i++) e = gsubst(e,z[i],gel(r,i));
+  for(i=1;i<j;i++) (void)delete_var();
   return gerepileupto(ltop,e);
 }
 
-- 
1.7.2.5