Create KojimaHash1.swift

Author: STREGA

Sources/GateUtilities/KojimaHash1.swift

@@ -0,0 +1,102 @@
+/*
+ * Copyright © 2025 Dustin Collins (Strega's Gate)
+ * All Rights Reserved.
+ *
+ * http://stregasgate.com
+ */
+
+/**
+ Create a unique identifier from a file name.
+ 
+ This hashing function was used by Metal Gear Solid 1 to efficiently reference files at reduced performance cost and 
+ memory usage compared to string comparisons. 
+ This hashing method has been dubbed "KojimaHash" by the MGS reversing community.
+ 
+ - warning: Due to the lower bit width (16bit), this hash is more likeley to have collisions. 
+ Keep track of the generated hashes to ensure there are no collisions. 
+ */
+public struct KojimaHash1 {
+    public let value: UInt16
+    
+    public init(_ hash: UInt16) {
+        self.value = hash
+    }
+    
+    public init?(hexString: String) {
+        self.value = Self.hash(from: hexString)
+    }
+    
+    public init?(filename: String) {
+        self.value = Self.hash(from: filename)
+    }
+    
+    /// Create a hash value from a filename string
+    public static func hash(from filename: String) -> UInt16 {
+        var hash: UInt16 = 0
+        for c in filename.split(separator: ".")[0].utf8 {
+            hash = (( hash >> 11 ) | ( hash << 5 ))
+            hash = hash &+ UInt16(c)
+        }
+        return hash
+    }
+    
+    public static func hash(from hexString: String) -> UInt16? {
+        return UInt16(hexString, radix: 16)
+    }
+    
+    public static func string(from hashValue: UInt16) -> String {
+        return String(hashValue, radix: 16, uppercase: true)
+    }
+}
+
+extension KojimaHash1: Codable {}
+extension KojimaHash1: Sendable {}
+
+extension KojimaHash1: Identifiable {
+    public var id: UInt16 {
+        return self.value
+    }
+}
+
+extension KojimaHash1: Comparable {
+    public static func < (lhs: KojimaHash1, rhs: KojimaHash1) -> Bool {
+        return lhs.value < rhs.value
+    }
+}
+
+extension KojimaHash1: Equatable {
+    public static func == (lhs: KojimaHash1, rhs: KojimaHash1) -> Bool {
+        return lhs.value == rhs.value
+    }
+}
+
+extension KojimaHash1: Hashable {
+    public func hash(into hasher: inout Hasher) {
+        hasher.combine(self.value)
+    }
+}
+
+extension KojimaHash1: CustomStringConvertible, CustomDebugStringConvertible {
+    public var description: String {
+        return Self.string(from: self.value)
+    }
+    public var debugDescription: String {
+        return "0x" + Self.string(from: self.value)
+    }
+}
+
+extension KojimaHash1: BinaryCodable {
+    public func encode(into data: inout ContiguousArray<UInt8>, version: BinaryCodableVersion) throws {
+        try self.value.encode(into: &data, version: version)
+    }
+    public init(decoding data: UnsafeRawBufferPointer, at offset: inout Int, version: BinaryCodableVersion) throws {
+        self.value = try .init(decoding: data, at: &offset, version: version)
+    }
+}
+
+extension KojimaHash1: ExpressibleByIntegerLiteral {
+    public typealias IntegerLiteralType = UInt16
+    public init(integerLiteral value: UInt16) {
+        self.init(value)
+    }
+}