Generalize BCD helpers to FixedWidthInteger; add encoder + tests

Author: mickeyl

Sources/CornucopiaCore/Extensions/FixedWidthInteger/FixedWidthInteger+BCD.swift

@@ -0,0 +1,27 @@
+//
+//  Cornucopia – (C) Dr. Lauer Information Technology
+//
+public extension FixedWidthInteger {
+
+    /// Returns the corresponding BCD-decoded decimal, or `-1`, if the encoding is invalid.
+    /// NOTE: Only values in the range `0x00`...`0x99` are considered valid.
+    var CC_BCD: Int {
+        guard self >= 0 && self <= 0xFF else { return -1 }
+        let value = UInt8(truncatingIfNeeded: self)
+        let highNibble = value >> 4
+        guard highNibble < 10 else { return -1 }
+        let loNibble = value & 0x0F
+        guard loNibble < 10 else { return -1 }
+        return Int(highNibble * 10 + loNibble)
+    }
+
+    /// Returns the BCD-encoded byte for a decimal value (00...99), or `nil` if out of range.
+    func CC_toBCD() -> Self? {
+        guard self >= 0 && self <= 99 else { return nil }
+        let value = UInt8(truncatingIfNeeded: self)
+        let highNibble = (value / 10) << 4
+        let loNibble = value % 10
+        let encoded = Int(highNibble | loNibble)
+        return Self(exactly: encoded)
+    }
+}

Sources/CornucopiaCore/Extensions/UInt8/UInt8+BCD.swift

@@ -0,0 +1,37 @@
+import XCTest
+
+import CornucopiaCore
+
+class FixedWidthInteger_BCD_Tests: XCTestCase {
+
+    func testDecodeValid() {
+
+        XCTAssertEqual(UInt8(0x00).CC_BCD, 0)
+        XCTAssertEqual(UInt8(0x42).CC_BCD, 42)
+        XCTAssertEqual(UInt16(0x99).CC_BCD, 99)
+        XCTAssertEqual(Int(0x10).CC_BCD, 10)
+    }
+
+    func testDecodeInvalid() {
+
+        XCTAssertEqual(UInt8(0xFA).CC_BCD, -1)
+        XCTAssertEqual(UInt16(0x12A).CC_BCD, -1)
+        XCTAssertEqual(Int(0x0F).CC_BCD, -1)
+        XCTAssertEqual(Int(-1).CC_BCD, -1)
+    }
+
+    func testEncodeValid() {
+
+        XCTAssertEqual(UInt8(45).CC_toBCD(), 0x45)
+        XCTAssertEqual(UInt16(90).CC_toBCD(), 0x90)
+        XCTAssertEqual(Int(99).CC_toBCD(), 0x99)
+    }
+
+    func testEncodeInvalid() {
+
+        XCTAssertNil(Int(-1).CC_toBCD())
+        XCTAssertNil(Int(100).CC_toBCD())
+        XCTAssertNil(UInt16(120).CC_toBCD())
+        XCTAssertNil(Int8(80).CC_toBCD())
+    }
+}