handle zero corner case

breandan · May 25, 2024 · 8471026 · 8471026
1 parent 4fe1d5f
commit 8471026
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Showing 2 changed files with 5 additions and 4 deletions.
diff --git a/src/commonMain/kotlin/ai/hypergraph/kaliningraph/parsing/SeqValiant.kt b/src/commonMain/kotlin/ai/hypergraph/kaliningraph/parsing/SeqValiant.kt
@@ -145,11 +145,12 @@ class PTree(val root: String = ".ε", val branches: List<Π2A<PTree>> = listOf()
     }
 
   fun sampleStrWithoutReplacement(stride: Int = 1, offset: Int = 0): Sequence<String> =
-    if (totalTrees.bitLength() < 5) sequence {
+    if (6 < totalTrees.bitLength())
+      bigLFSRSequence(totalTrees).mapIndexedNotNull { index, i -> if (index % stride == offset) newDecoder(i) else null }
+    else sequence {
       var i = BigInteger.ZERO
       while (i < totalTrees) { yield(newDecoder(i)); i++}
-    } else bigLFSRSequence(totalTrees)
-      .mapIndexedNotNull { index, i -> if (index % stride == offset) newDecoder(i) else null }
+    }
 
   fun sampleStrWithPCFG5(pcfgTable: Map<Int, Int>): Sequence<String> =
     sequence { while (true) yield(samplePCFG5(pcfgTable)) }

diff --git a/src/commonMain/kotlin/ai/hypergraph/kaliningraph/sampling/Samplers.kt b/src/commonMain/kotlin/ai/hypergraph/kaliningraph/sampling/Samplers.kt
@@ -297,7 +297,7 @@ class BigLFSR(primitivePoly: BigInteger, val start: BigInteger = BigInteger.ONE)
       val shiftedOutA1: Boolean = last.bitAt(0)
       next = last.shr(1)
       if (shiftedOutA1) { next = next.xor(taps) }
-      if (next == start) break else yield(next)
+      if (next == start) { yield(BigInteger.ZERO); break } else yield(next)
       last = next
     }
   }