map seed calculation (#3)

pkg/utils/map_seed_hash.go

@@ -0,0 +1,37 @@
+package utils
+
+import "math"
+
+const mapHashDivisor = 1 << 16
+
+func GetMapSeed(initHashSeed, endHashSeed uint) (uint, bool) {
+	var gameSeedXor uint = 0
+	seed, found := reverseMapSeedHash(endHashSeed)
+	if found {
+		gameSeedXor = initHashSeed ^ seed
+	}
+
+	if gameSeedXor == 0 {
+		return 0, false
+	}
+
+	return seed, true
+}
+
+func reverseMapSeedHash(hash uint) (uint, bool) {
+	incrementalValue := uint(1)
+
+	for startValue := uint(0); startValue < math.MaxUint; startValue += incrementalValue {
+		seedResult := (uint(startValue)*0x6AC690C5 + 666) & 0xFFFFFFFF
+
+		if seedResult == hash {
+			return startValue, true
+		}
+
+		if incrementalValue == 1 && (seedResult%mapHashDivisor) == (hash%mapHashDivisor) {
+			incrementalValue = mapHashDivisor
+		}
+	}
+
+	return 0, false
+}