[Guile-commits] GNU Guile branch, stable-2.0, updated. v2.0.7-145-ga2dead1

[Mark H Weaver]

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http://git.savannah.gnu.org/cgit/guile.git/commit/?id=a2dead1b0fb6523598e3acbbe91127eaf47fe98c

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- Log -----------------------------------------------------------------
commit a2dead1b0fb6523598e3acbbe91127eaf47fe98c
Author: Mark H Weaver <address@hidden>
Date:   Sun Mar 3 04:34:17 2013 -0500

    Improve code in scm_gcd for inum/inum case
    
    * libguile/numbers.c (scm_gcd): Improve implementation of inum/inum case
      to be more clear and efficient.

-----------------------------------------------------------------------

Summary of changes:
 libguile/numbers.c |   54 ++++++++++++++++++++++++++++-----------------------
 1 files changed, 30 insertions(+), 24 deletions(-)

diff --git a/libguile/numbers.c b/libguile/numbers.c
index 66c95db..9c28a79 100644
--- a/libguile/numbers.c
+++ b/libguile/numbers.c
@@ -3889,52 +3889,58 @@ SCM_PRIMITIVE_GENERIC (scm_i_gcd, "gcd", 0, 2, 1,
 SCM
 scm_gcd (SCM x, SCM y)
 {
-  if (SCM_UNBNDP (y))
+  if (SCM_UNLIKELY (SCM_UNBNDP (y)))
     return SCM_UNBNDP (x) ? SCM_INUM0 : scm_abs (x);
   
-  if (SCM_I_INUMP (x))
+  if (SCM_LIKELY (SCM_I_INUMP (x)))
     {
-      if (SCM_I_INUMP (y))
+      if (SCM_LIKELY (SCM_I_INUMP (y)))
         {
           scm_t_inum xx = SCM_I_INUM (x);
           scm_t_inum yy = SCM_I_INUM (y);
           scm_t_inum u = xx < 0 ? -xx : xx;
           scm_t_inum v = yy < 0 ? -yy : yy;
           scm_t_inum result;
-          if (xx == 0)
+          if (SCM_UNLIKELY (xx == 0))
            result = v;
-         else if (yy == 0)
+         else if (SCM_UNLIKELY (yy == 0))
            result = u;
          else
            {
-             scm_t_inum k = 1;
-             scm_t_inum t;
+             int k = 0;
              /* Determine a common factor 2^k */
-             while (!(1 & (u | v)))
+             while (((u | v) & 1) == 0)
                {
-                 k <<= 1;
+                 k++;
                  u >>= 1;
                  v >>= 1;
                }
              /* Now, any factor 2^n can be eliminated */
-             if (u & 1)
-               t = -v;
+             if ((u & 1) == 0)
+               while ((u & 1) == 0)
+                 u >>= 1;
              else
+               while ((v & 1) == 0)
+                 v >>= 1;
+             /* Both u and v are now odd.  Subtract the smaller one
+                from the larger one to produce an even number, remove
+                more factors of two, and repeat. */
+             while (u != v)
                {
-                 t = u;
-               b3:
-                 t = SCM_SRS (t, 1);
+                 if (u > v)
+                   {
+                     u -= v;
+                     while ((u & 1) == 0)
+                       u >>= 1;
+                   }
+                 else
+                   {
+                     v -= u;
+                     while ((v & 1) == 0)
+                       v >>= 1;
+                   }
                }
-             if (!(1 & t))
-               goto b3;
-             if (t > 0)
-               u = t;
-             else
-               v = -t;
-             t = u - v;
-             if (t != 0)
-               goto b3;
-             result = u * k;
+             result = u << k;
            }
           return (SCM_POSFIXABLE (result)
                  ? SCM_I_MAKINUM (result)


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