use std lib function in pmmr for all_ones() and most_significant_pos() (#924)

* use std lib function in pmmr for all_ones() and most_significant_pos()

* fix all_ones() edge case with 0 and add comparison tests with old functions

core/src/core/pmmr.rs

@@ -987,28 +987,13 @@ fn bintree_jump_left(num: u64) -> u64 {
 
 // Check if the binary representation of a number is all ones.
 fn all_ones(num: u64) -> bool {
-	if num == 0 {
-		return false;
-	}
-	let mut bit = 1;
-	while num >= bit {
-		if num & bit == 0 {
-			return false;
-		}
-		bit = bit << 1;
-	}
-	true
+	let ones = num.count_ones();
+	num.leading_zeros() + ones == 64 && ones > 0
 }
 
 // Get the position of the most significant bit in a number.
 fn most_significant_pos(num: u64) -> u64 {
-	let mut pos = 0;
-	let mut bit = 1;
-	while num >= bit {
-		bit = bit << 1;
-		pos += 1;
-	}
-	pos
+	64 - u64::from(num.leading_zeros())
 }
 
 #[cfg(test)]
@@ -1140,7 +1125,7 @@ mod test {
 		for n in vec![1, 7, 255] {
 			assert!(all_ones(n), "{} should be all ones", n);
 		}
-		for n in vec![6, 9, 128] {
+		for n in vec![0, 6, 9, 128] {
 			assert!(!all_ones(n), "{} should not be all ones", n);
 		}
 	}
@@ -1915,4 +1900,45 @@ mod test {
 		assert_eq!(n_leaves(9), 6);
 		assert_eq!(n_leaves(10), 6);
 	}
+
+
+	#[test]
+	fn check_all_ones() {
+		for i in 0..1000000 {
+			assert_eq!(old_all_ones(i),all_ones(i));
+		}
+	}
+
+	// Check if the binary representation of a number is all ones.
+	fn old_all_ones(num: u64) -> bool {
+		if num == 0 {
+			return false;
+		}
+		let mut bit = 1;
+		while num >= bit {
+			if num & bit == 0 {
+				return false;
+			}
+			bit = bit << 1;
+		}
+		true
+	}
+
+	#[test]
+	fn check_most_significant_pos() {
+		for i in 0u64..1000000 {
+			assert_eq!(old_most_significant_pos(i),most_significant_pos(i));
+		}
+	}
+
+	// Get the position of the most significant bit in a number.
+	fn old_most_significant_pos(num: u64) -> u64 {
+		let mut pos = 0;
+		let mut bit = 1;
+		while num >= bit {
+			bit = bit << 1;
+			pos += 1;
+		}
+		pos
+	}
 }