bitfield: minor documentation and function tweaks (#10549)

vlib/bitfield/bitfield.v

@@ -340,6 +340,8 @@ pub fn (instance BitField) clone() BitField {
 
 // cmp compares two bit arrays bit by bit and returns 'true' if they are
 // identical by length and contents and 'false' otherwise.
+[deprecated: 'use a == b instead']
+[deprecated_after: '2021-06-29']
 pub fn (instance BitField) cmp(input BitField) bool {
 	if instance.size != input.size {
 		return false
@@ -352,6 +354,18 @@ pub fn (instance BitField) cmp(input BitField) bool {
 	return true
 }
 
+pub fn (a BitField) == (b BitField) bool {
+	if a.size != b.size {
+		return false
+	}
+	for i in 0 .. zbitnslots(a.size) {
+		if a.field[i] != b.field[i] {
+			return false
+		}
+	}
+	return true
+}
+
 // pop_count returns the number of set bits (ones) in the array.
 pub fn (instance BitField) pop_count() int {
 	size := instance.size
@@ -391,7 +405,7 @@ pub fn (haystack BitField) pos(needle BitField) int {
 	}
 	for i := 0; i <= diff; i++ {
 		needle_candidate := haystack.slice(i, needle_size + i)
-		if needle_candidate.cmp(needle) {
+		if needle_candidate == needle {
 			// needle matches a sub-array of haystack; return starting position of the sub-array
 			return i
 		}