Add a way to readSignedBits

Author: Cosmo

Sources/BinaryKit/Binary.swift

@@ -327,3 +327,12 @@ public struct Binary {
         bytesStore.append(contentsOf: int.bytes)
     }
 }
+
+
+extension Binary {
+    mutating func readSignedBits(_ quantity: UInt8) throws -> Int {
+        let multiplicationFactor = (try readBit() == 1) ? -1 : 1
+        let value = try readBits(quantity - 1)
+        return value * multiplicationFactor
+    }
+}

Tests/BinaryKitTests/BinaryKitTests.swift

@@ -314,6 +314,18 @@ final class BinaryKitTests: XCTestCase {
         XCTAssertEqual(try bin.readBits(13), 0x11ff)
     }
 
+    func testSignedBits() {
+        var binary = Binary(bytes: [0xFF, 0x7F, 0x00, 0xFF, 0x77, 0xFF, 0xFF])
+        XCTAssertEqual(try binary.readSignedBits(8), -127)
+        XCTAssertEqual(try binary.readSignedBits(8), 127)
+        XCTAssertEqual(try binary.readSignedBits(8), 0)
+        XCTAssertEqual(try binary.readSignedBits(4), -7)
+        XCTAssertEqual(try binary.readSignedBits(4), -7)
+        XCTAssertEqual(try binary.readSignedBits(4), 7)
+        XCTAssertEqual(try binary.readSignedBits(4), 7)
+        XCTAssertEqual(try binary.readSignedBits(16), -32767)
+    }
+    
     // MARK: -
 
     static var allTests = [