#154 Fixed FixedWidthInteger.toHexadecimal() support for Embedded S…

…wift

Sources/Bluetooth/Extensions/Hexadecimal.swift

@@ -9,12 +9,26 @@
 internal extension FixedWidthInteger {
 
     func toHexadecimal() -> String {
-
-        var string = String(self, radix: 16)
-        while string.utf8.count < (MemoryLayout<Self>.size * 2) {
+        let length = MemoryLayout<Self>.size * 2
+        var string: String
+        #if hasFeature(Embedded) || (canImport(Darwin) && DEBUG)
+        string = ""
+        string.reserveCapacity(length)
+        self.bigEndian.bytes.forEach { byte in
+            string.append(String(format: "%02X", length: 2, byte)!)
+        }
+        #else // Linux and non-Embedded release builds use Swift StdLib
+        string = String(self, radix: 16, uppercase: true)
+        // Add Zero padding
+        while string.utf8.count < length {
             string = "0" + string
         }
-        return string.uppercased()
+        #endif
+        assert(string.utf8.count == length)
+        #if !hasFeature(Embedded)
+        assert(string == string.uppercased(), "String should be uppercased")
+        #endif
+        return string
     }
 }
 

Sources/Bluetooth/Extensions/String.swift

@@ -5,6 +5,10 @@
 //  Created by Alsey Coleman Miller on 11/4/24.
 //
 
+#if canImport(Darwin)
+import Darwin
+#endif
+
 internal extension String {
 
     /// Initialize from UTF8 data.
@@ -19,4 +23,28 @@ internal extension String {
         }
         #endif
     }
+
+    #if hasFeature(Embedded)
+    // Can't use `CVarArg` in Embedded Swift
+    init?(format: String, length: Int, _ value: UInt8) {
+        var cString: [CChar] = .init(repeating: 0, count: length + 1)
+        guard _snprintf_uint8_t(&cString, cString.count, format, value) >= 0 else {
+            return nil
+        }
+        self.init(cString: cString)
+    }
+    #elseif canImport(Darwin)
+    init?<T: CVarArg>(format: String, length: Int, _ value: T) {
+        var cString: [CChar] = .init(repeating: 0, count: length + 1)
+        guard snprintf(ptr: &cString, cString.count, format, value) >= 0 else {
+            return nil
+        }
+        self.init(cString: cString)
+    }
+    #endif
 }
+
+#if hasFeature(Embedded)
+@_silgen_name("snprintf")
+internal func _snprintf_uint8_t(_ pointer: UnsafeMutablePointer<CChar>, _ length: Int, _ format: UnsafePointer<CChar>, _ arg: UInt8) -> Int32
+#endif