Created
April 18, 2011 14:21
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O(log(N)) な フィボナッチ数の計算方法ベンチマーク
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object FibImpModule { | |
/** リファレンス実装 */ | |
val fibRef: Stream[BigInt] = | |
BigInt(0) #:: fibRef.scanLeft(BigInt(1)){_ + _} | |
/** 逐次平方変換系の実装 */ | |
// Generic な実装 (しかし、JVMの型消去のため、実力よりずいぶん遅くなったため | |
// 公正なベンチマークにならないのでボツ。。。) | |
def fibSqr[IntT](n: Int)(implicit num: Integral[IntT]): IntT = { | |
import num._ | |
@scala.annotation.tailrec // 末尾再帰最適化を保証するためのアノーテーション | |
def rec(a: IntT, b: IntT, p: IntT, q: IntT, count: Int): IntT = { | |
if (count == 0) b | |
else (count % 2) match { | |
case 0 => rec(a, b, p*p+q*q, num.fromInt(2)*p*q+q*q, count / 2) | |
case 1 => rec(b*q+a*q+a*p, b*p+a*q, p, q, count - 1) | |
} | |
} | |
rec(one, one, zero, one, n) | |
} | |
// Int 専用 | |
def fibSqrInt(n: Int): Int = { | |
@scala.annotation.tailrec // 末尾再帰最適化を保証するためのアノーテーション | |
def rec(a: Int, b: Int, p: Int, q: Int, count: Int): Int = { | |
if (count == 0) b | |
else (count % 2) match { | |
case 0 => rec(a, b, p*p+q*q, 2*p*q+q*q, count / 2) | |
case 1 => rec(b*q+a*q+a*p, b*p+a*q, p, q, count - 1) | |
} | |
} | |
rec(1, 1, 0, 1, n) | |
} | |
// Long 専用 | |
def fibSqrLong(n: Int): Long = { | |
@scala.annotation.tailrec // 末尾再帰最適化を保証するためのアノーテーション | |
def rec(a: Long, b: Long, p: Long, q: Long, count: Long): Long = { | |
if (count == 0) b | |
else (count % 2) match { | |
case 0 => rec(a, b, p*p+q*q, 2*p*q+q*q, count / 2) | |
case 1 => rec(b*q+a*q+a*p, b*p+a*q, p, q, count - 1) | |
} | |
} | |
rec(1, 1, 0, 1, n) | |
} | |
// BigInt 専用 | |
def fibSqrBigInt(n: Int): BigInt = { | |
@scala.annotation.tailrec // 末尾再帰最適化を保証するためのアノーテーション | |
def rec(a: BigInt, b: BigInt, p: BigInt, q: BigInt, count: Int): BigInt = { | |
if (count == 0) b | |
else (count % 2) match { | |
case 0 => rec(a, b, p*p+q*q, p*q*2+q*q, count / 2) | |
case 1 => rec(b*q+a*q+a*p, b*p+a*q, p, q, count - 1) | |
} | |
} | |
rec(1, 1, 0, 1, n) | |
} | |
/** 対角要素冪の実装 */ | |
// pow を使った | |
def fibDigDoublePow(n: Int): Long = | |
math.round(0.4472135954999579 * math.pow(1.618033988749895, n)) | |
// exp を使った | |
def fibDigDoubleExp(n: Int): Long = | |
(0.4472135954999579 * math.exp(0.48121182505960347 * n) + 0.5).asInstanceOf[Long] | |
/** LF 系 */ | |
// Luca number & Fibonacci number | |
// http://en.wikipedia.org/wiki/Lucas_number | |
def fibLucaInt(n: Int): Int = { | |
@annotation.tailrec | |
def rec(l: Int, f: Int, bitmask: Int): Int = | |
if (bitmask == 0) f | |
else { | |
val ll = (l * l + 5 * f * f) >> 1 | |
val ff = l * f | |
if ((n & bitmask) == 0) rec(ll, ff, bitmask >> 1) | |
else rec((ll + 5 * ff) >> 1, (ll + ff) >> 1, bitmask >> 1) | |
} | |
rec(1, 1, Integer.highestOneBit(n) >> 1) | |
} | |
} |
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