February 2017
Intermediate to advanced
368 pages
8h 21m
Japanese
Content preview from Optimized C++ ―最適化、高速化のためのプログラミングテクニック
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57
3.5 ホットなコードを探し出すためにコードのコストを見積もる
Stopwatch sw("function_to_be_timed()");
for (counter_t i = 0; i < iterations; ++i) {
result = function_to_be_timed();
}
}
反復回数はだいたいで求めるしかない。全実行時間は、デスクトッププロセッサで
Stopwatch
の
使う
tick
カウンタが
10
ミリ秒の分解能なら、数百から数千ミリ秒であるべきだ。
十分に簡単な関数については、変数が
64
ビットの
unsigned long long
型でないといけないこ
とがあるので、私は
unsigned
や
unsigned long
ではなく
counter_t
型を使う。
typedef
を使うの
に慣れれば、戻ってすべての型名を書き換えるのに比べればずっと容易だ。最適化プロセスそのも
のの最適化である。
波括弧の外側のものは重要だ。
Stopwatch
クラスのインスタンス
sw
のスコープを定義するから
だ。
Stopwatch
が
RAII
イディオムを使うので、
sw
コンストラクタは開始
tick
カウントを、デスト
ラクタは最終
tick
カウントを得て、標準出力ストリームに結果を出す。
3.5
ホットなコードを探し出すためにコードのコストを見積もる
プロファイルと実行時間計測が最適化候補を見つけるために効果的だということは経験から学ん
だ。プロファイラは、非常に多く呼ばれる関数や全体の処理時間のかなりの部分を占める関数を指 ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.