X-Git-Url: http://git.subgeniuskitty.com/surreal-numbers/.git/blobdiff_plain/c3b4805541f68c1dccc4e7007fdb7c828bb86f8f..8be725f2ca1fc13ac01f8f3a553e6a8803d08d91:/chapter-1-experiments/ch1-breeding-numbers.go

diff --git a/chapter-1-experiments/ch1-breeding-numbers.go b/chapter-1-experiments/ch1-breeding-numbers.go
index 58576cc..fc1c397 100644
--- a/chapter-1-experiments/ch1-breeding-numbers.go
+++ b/chapter-1-experiments/ch1-breeding-numbers.go
@@ -300,7 +300,11 @@ func main() {
 // right sets. This covers all the reduced form permutations. Any longer
 // permutations will be similar to one of the reduced forms.
 func permuteExistingNumbers(generation int, universe surrealUniverse) []surrealNumber {
-    var numbers []surrealNumber
+    // Profiling indicates that most calls to growSlice() and memMove()
+    // originate in this function. Allocating a sufficiently large slice
+    // upfront results in 2x speed improvement and 1/3 reduction in heap usage.
+    numberOfPermutations := ((universe.cardinality()+1) * (universe.cardinality()+1)) - 1
+    numbers := make([]surrealNumber, 0, numberOfPermutations)
 
     // First build permutations with 1 element in each set.
     for i := 0; i < universe.cardinality(); i++ {