diff --git a/bithack.go b/bithack.go
index be13d69..19847d7 100644
--- a/bithack.go
+++ b/bithack.go
@@ -22,6 +22,12 @@ func makeUint64BucketArray(size int) unsafe.Pointer {
 }
 
 func matchTopHash(tophash [bucketCnt]uint8, top uint8) bitmask64 {
+	// For the technique, see:
+	// http://graphics.stanford.edu/~seander/bithacks.html##ValueInWord
+	// (Determine if a word has a byte equal to n).
+	//
+	// The idea comes from SwissTable C++ version:
+	// https://github.com/abseil/abseil-cpp/blob/master/absl/container/internal/raw_hash_set.h#L661
 	ctrl := littleEndianBytesToUint64(tophash)
 	cmp := ctrl ^ (lsbs * uint64(top))
 	return bitmask64((cmp - lsbs) & ^cmp & msbs)
diff --git a/readme.md b/readme.md
index 087fa86..51593d5 100644
--- a/readme.md
+++ b/readme.md
@@ -2,7 +2,7 @@
 
 umap is a fast, reliable, simple hashmap that only supports the uint64 key/value pair. It is faster than the runtime hashmap in most cases.
 
-The umap is mainly based on the SwissTable(https://github.com/abseil/abseil-cpp/blob/master/absl/container/internal/raw_hash_set.h).
+The umap is mainly based on the SwissTable(https://github.com/abseil/abseil-cpp/blob/master/absl/container/internal/raw_hash_set.h), it is portable for all platforms and doesn't require SSE or AVX.
 
 ## QuickStart