Implement bit shift operations in BitSet

Author: Heraldk

Bit Set/BitSet.playground/Contents.swift

@@ -89,3 +89,23 @@ z.all1()        // false
 
 //var bigBits = BitSet(size: 10000)
 //print(bigBits)
+
+var smallBitSet = BitSet(size: 16)
+smallBitSet[5] = true
+smallBitSet[10] = true
+print( smallBitSet >> 3 )
+print( smallBitSet << 6 ) // one bit shifts off the end
+
+var bigBitSet = BitSet( size: 120 )
+bigBitSet[1] = true
+bigBitSet[3] = true
+bigBitSet[7] = true
+bigBitSet[32] = true
+bigBitSet[55] = true
+bigBitSet[64] = true
+bigBitSet[80] = true
+print( bigBitSet )
+print( bigBitSet << 32 )
+print( bigBitSet << 64 )
+print( bigBitSet >> 32 )
+print( bigBitSet >> 64 )

Bit Set/BitSet.playground/Sources/BitSet.swift

@@ -9,7 +9,7 @@ public struct BitSet {
     We store the bits in a list of unsigned 64-bit integers.
     The first entry, `words[0]`, is the least significant word.
   */
-  private let N = 64
+  fileprivate let N = 64
   public typealias Word = UInt64
   fileprivate(set) public var words: [Word]
 
@@ -221,6 +221,50 @@ prefix public func ~ (rhs: BitSet) -> BitSet {
   return out
 }
 
+// MARK: - Bit shift operations
+
+/*
+ Note: For bitshift operations, the assumption is that any bits that are
+ shifted off the end of the end of the declared size are not still set.
+ In other words, we are maintaining the original number of bits.
+ */
+
+public func << (lhs: BitSet, numBitsLeft: Int) -> BitSet {
+    var out = lhs
+    let offset = numBitsLeft / lhs.N
+    let shift = numBitsLeft % lhs.N
+    for i in 0..<lhs.words.count {
+        out.words[i] = 0
+        if( i - offset >= 0 ) {
+            out.words[i] = lhs.words[i - offset] << shift
+        }
+        if( i - offset - 1 >= 0 ) {
+            out.words[i] |= lhs.words[i - offset - 1] >> (lhs.N - shift)
+        }
+    }
+    
+    out.clearUnusedBits()
+    return out
+}
+
+public func >> (lhs: BitSet, numBitsRight: Int) -> BitSet {
+    var out = lhs
+    let offset = numBitsRight / lhs.N
+    let shift = numBitsRight % lhs.N
+    for i in 0..<lhs.words.count {
+        out.words[i] = 0
+        if( i + offset < lhs.words.count ) {
+            out.words[i] = lhs.words[i + offset] >> shift
+        }
+        if( i + offset + 1 < lhs.words.count ) {
+            out.words[i] |= lhs.words[i + offset + 1] << (lhs.N - shift)
+        }
+    }
+    
+    out.clearUnusedBits()
+    return out
+}
+
 // MARK: - Debugging
 
 extension UInt64 {

Bit Set/BitSet.swift

@@ -9,7 +9,7 @@ public struct BitSet {
    We store the bits in a list of unsigned 64-bit integers.
    The first entry, `words[0]`, is the least significant word.
    */
-  private let N = 64
+  fileprivate let N = 64
   public typealias Word = UInt64
   fileprivate(set) public var words: [Word]
 
@@ -221,6 +221,51 @@ prefix public func ~ (rhs: BitSet) -> BitSet {
   return out
 }
 
+// MARK: - Bit shift operations
+
+/*
+ Note: For bitshift operations, the assumption is that any bits that are
+ shifted off the end of the end of the declared size are not still set.
+ In other words, we are maintaining the original number of bits.
+ */
+
+public func << (lhs: BitSet, numBitsLeft: Int) -> BitSet {
+    var out = lhs
+    let offset = numBitsLeft / lhs.N
+    let shift = numBitsLeft % lhs.N
+    for i in 0..<lhs.words.count {
+        out.words[i] = 0
+        if( i - offset >= 0 ) {
+            out.words[i] = lhs.words[i - offset] << shift
+        }
+        if( i - offset - 1 >= 0 ) {
+            out.words[i] |= lhs.words[i - offset - 1] >> (lhs.N - shift)
+        }
+    }
+    
+    out.clearUnusedBits()
+    return out
+}
+
+public func >> (lhs: BitSet, numBitsRight: Int) -> BitSet {
+    var out = lhs
+    let offset = numBitsRight / lhs.N
+    let shift = numBitsRight % lhs.N
+    for i in 0..<lhs.words.count {
+        out.words[i] = 0
+        if( i + offset < lhs.words.count ) {
+            out.words[i] = lhs.words[i + offset] >> shift
+        }
+        if( i + offset + 1 < lhs.words.count ) {
+            out.words[i] |= lhs.words[i + offset + 1] << (lhs.N - shift)
+        }
+    }
+    
+    out.clearUnusedBits()
+    return out
+}
+
+
 // MARK: - Debugging
 
 extension UInt64 {