The 'extendMaybe' function is seemingly *not* inlined in Go. Yet it

is systematically called when we set values, to check whether the backing
array need to be extended.

By bringing the check (the branch) in the calling function, we reduce the
number of function calls.

This leads to a ~10% performance gain in some  benchmarks.

bitset.go

@@ -135,24 +135,22 @@ func (b *BitSet) Len() uint {
 	return b.length
 }
 
-// extendSetMaybe adds additional words to incorporate new bits if needed
-func (b *BitSet) extendSetMaybe(i uint) {
-	if i >= b.length { // if we need more bits, make 'em
-		if i >= Cap() {
-			panic("You are exceeding the capacity")
-		}
-		nsize := wordsNeeded(i + 1)
-		if b.set == nil {
-			b.set = make([]uint64, nsize)
-		} else if cap(b.set) >= nsize {
-			b.set = b.set[:nsize] // fast resize
-		} else if len(b.set) < nsize {
-			newset := make([]uint64, nsize, 2*nsize) // increase capacity 2x
-			copy(newset, b.set)
-			b.set = newset
-		}
-		b.length = i + 1
+// extendSet adds additional words to incorporate new bits if needed
+func (b *BitSet) extendSet(i uint) {
+	if i >= Cap() {
+		panic("You are exceeding the capacity")
 	}
+	nsize := wordsNeeded(i + 1)
+	if b.set == nil {
+		b.set = make([]uint64, nsize)
+	} else if cap(b.set) >= nsize {
+		b.set = b.set[:nsize] // fast resize
+	} else if len(b.set) < nsize {
+		newset := make([]uint64, nsize, 2*nsize) // increase capacity 2x
+		copy(newset, b.set)
+		b.set = newset
+	}
+	b.length = i + 1
 }
 
 // Test whether bit i is set.
@@ -170,7 +168,9 @@ func (b *BitSet) Test(i uint) bool {
 // may lead to a memory shortage and a panic: the caller is responsible
 // for providing sensible parameters in line with their memory capacity.
 func (b *BitSet) Set(i uint) *BitSet {
-	b.extendSetMaybe(i)
+	if i >= b.length { // if we need more bits, make 'em
+		b.extendSet(i)
+	}
 	b.set[i>>log2WordSize] |= 1 << (i & (wordSize - 1))
 	return b
 }
@@ -218,8 +218,9 @@ func (b *BitSet) FlipRange(start, end uint) *BitSet {
 	if start >= end {
 		return b
 	}
-
-	b.extendSetMaybe(end - 1)
+	if end-1 >= b.length { // if we need more bits, make 'em
+		b.extendSet(end - 1)
+	}
 	var startWord uint = start >> log2WordSize
 	var endWord uint = end >> log2WordSize
 	b.set[startWord] ^= ^(^uint64(0) << (start & (wordSize - 1)))
@@ -671,7 +672,9 @@ func (b *BitSet) InPlaceIntersection(compare *BitSet) {
 		b.set[i] = 0
 	}
 	if compare.length > 0 {
-		b.extendSetMaybe(compare.length - 1)
+		if compare.length-1 >= b.length {
+			b.extendSet(compare.length - 1)
+		}
 	}
 }
 
@@ -710,8 +713,8 @@ func (b *BitSet) InPlaceUnion(compare *BitSet) {
 	if l > int(b.wordCount()) {
 		l = int(b.wordCount())
 	}
-	if compare.length > 0 {
-		b.extendSetMaybe(compare.length - 1)
+	if compare.length > 0 && compare.length-1 >= b.length {
+		b.extendSet(compare.length - 1)
 	}
 	for i := 0; i < l; i++ {
 		b.set[i] |= compare.set[i]
@@ -758,8 +761,8 @@ func (b *BitSet) InPlaceSymmetricDifference(compare *BitSet) {
 	if l > int(b.wordCount()) {
 		l = int(b.wordCount())
 	}
-	if compare.length > 0 {
-		b.extendSetMaybe(compare.length - 1)
+	if compare.length > 0 && compare.length-1 >= b.length {
+		b.extendSet(compare.length - 1)
 	}
 	for i := 0; i < l; i++ {
 		b.set[i] ^= compare.set[i]