A-M baby

Task/Fibonacci-sequence/D/fibonacci-sequence-2.d

@@ -0,0 +1,30 @@
+import std.stdio, std.bigint;
+
+T fibonacciMatrix(T=BigInt)(size_t n) {
+    int[size_t.sizeof * 8] binDigits;
+    size_t nBinDigits;
+    while (n > 0) {
+        binDigits[nBinDigits] = n % 2;
+        n /= 2;
+        nBinDigits++;
+    }
+
+    T x=1, y, z=1;
+    foreach_reverse (b; binDigits[0 .. nBinDigits]) {
+        if (b) {
+            x = (x + z) * y;
+            y = y ^^ 2 + z ^^ 2;
+        } else {
+            auto x_old = x;
+            x = x ^^ 2 + y ^^ 2;
+            y = (x_old + z) * y;
+        }
+        z = x + y;
+    }
+
+    return y;
+}
+
+void main() {
+    writeln(fibonacciMatrix(1_000_000));
+}