Changeset 9cd697 in git

Timestamp:

Mar 21, 2011, 4:17:15 PM (13 years ago)

Author:

Frank Seelisch <seelisch@…>

Branches:

(u'spielwiese', 'fe61d9c35bf7c61f2b6cbf1b56e25e2f08d536cc')

Children:

45159ae4c7be1c7c2ec22897b2201afc05c0a81f

Parents:

a8b44d7ae81df1f427913b6461535b6f2a111997

Message:

changed (corrected) nDivBy over 2^m

git-svn-id: file:///usr/local/Singular/svn/trunk@14023 2c84dea3-7e68-4137-9b89-c4e89433aadc

File:

• kernel/rmodulo2m.cc (modified) (3 diffs)

kernel/rmodulo2m.cc

@@ -208 +208 @@
 }
 
-/* This does not seem to be the predicate whether a
-   is divisible by b in Z/2^m: if a is NULL then
-   the answer is not necessarily TRUE. */
+/* Is a divisible by b? There are two cases:
+   1) a = 0 mod 2^m; then TRUE iff b = 0 or b is a power of 2
+   2) a, b <> 0; then TRUE iff b/gcd(a, b) is a unit mod 2^m
+   TRUE iff b(gcd(a, b) is a unit */
 BOOLEAN nr2mDivBy (number a, number b)
 {
@@ -221 +222 @@
     {
       /* overflow: we need to check whether b
-         is a power of 2: */
+         is zero or a power of 2: */
       c = (NATNUMBER)b;
       while (c != 0)
@@ -232 +233 @@
   }
   else
-    return ((NATNUMBER)a % (NATNUMBER)b) == 0;
+  {
+    number n = nr2mGcd(a, b, currRing);
+    n = nr2mDiv(b, n);
+    return nr2mIsUnit(n);
+  }
 }