Better heuristics for univariate factorization over Z

PoslavskySV · May 2, 2022 · 8097385 · 8097385
1 parent cfd6722
commit 8097385
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Showing 4 changed files with 17 additions and 5 deletions.
diff --git a/rings.repl/rings.repl b/rings.repl/rings.repl
@@ -51,7 +51,7 @@ case $os in
     ;;
 esac
 
-ringsVersion=2.5.7
+ringsVersion=2.5.8
 ammArgs=()
 javaArgs=()
 

diff --git a/rings.scaladsl/build.sbt b/rings.scaladsl/build.sbt
@@ -4,11 +4,11 @@ organization := "cc.redberry"
 
 name := "rings.scaladsl"
 
-version := "2.5.7"
+version := "2.5.8"
 
 scalaVersion := "2.13.5"
 
-crossScalaVersions := Seq("2.11.12", "2.12.13", "2.13.5")
+crossScalaVersions := Seq("2.12.13", "2.13.5")
 
 moduleName := name.value
 

diff --git a/rings/src/main/java/cc/redberry/rings/poly/univar/UnivariateFactorization.java b/rings/src/main/java/cc/redberry/rings/poly/univar/UnivariateFactorization.java
@@ -391,7 +391,9 @@ private static int next32BitPrime(int val) {
     final static int
             N_MIN_MODULAR_FACTORIZATION_TRIALS = 2, // minimal number of modular trials
             N_SIMPLE_MOD_PATTERN_FACTORS = 12, // number of modular factors sufficient small enough to proceed to reconstruction
-            N_MODULAR_FACTORIZATION_TRIALS = 4; // maximal number of modular trials
+            N_MODULAR_FACTORIZATION_TRIALS = 4, // maximal number of modular trials
+            N_TOO_MUCH_FACTORS_COUNT = 22, // if there are more modular factors, then we will use more modular factorization attempts
+            N_MODULAR_FACTORIZATION_TRIALS_TOO_MUCH_FACTORS = 12; // maximal number of modular trials if there are too many factors
 
     /**
      * Factors primitive square-free polynomial using Hensel lifting
@@ -414,9 +416,13 @@ static PolynomialFactorDecomposition<UnivariatePolynomial<BigInteger>> FactorSqu
         UnivariatePolynomialZp64 moduloImage;
         PolynomialFactorDecomposition<UnivariatePolynomialZp64> lModularFactors = null;
 
-        for (int attempt = 0; attempt < N_MODULAR_FACTORIZATION_TRIALS; attempt++) {
+        for (int attempt = 0; ; attempt++) {
             if (attempt >= N_MIN_MODULAR_FACTORIZATION_TRIALS && lModularFactors.size() <= N_SIMPLE_MOD_PATTERN_FACTORS)
                 break;
+            if (attempt >= N_MODULAR_FACTORIZATION_TRIALS)
+                if (lModularFactors.size() < N_TOO_MUCH_FACTORS_COUNT
+                        || attempt >= N_MODULAR_FACTORIZATION_TRIALS_TOO_MUCH_FACTORS)
+                    break;
 
             long tmpModulus;
             do {

diff --git a/rings/src/test/java/cc/redberry/rings/poly/univar/UnivariateFactorizationTest.java b/rings/src/test/java/cc/redberry/rings/poly/univar/UnivariateFactorizationTest.java
@@ -553,4 +553,10 @@ public void test7() {
         UnivariatePolynomial<BigInteger> poly = UnivariatePolynomial.parse("x^259 - 1", Z, "x");
         assertEquals(4, Factor(poly).size());
     }
+
+    @Test(timeout = 100_000)
+    public void test10() {
+        UnivariatePolynomial<BigInteger> poly = UnivariatePolynomial.parse("x^70 + 1", Z, "x");
+        assertEquals(4, Factor(poly).size());
+    }
 }