November 2017
Beginner to intermediate
344 pages
7h 2m
Chinese
Content preview from 深入理解運算原理｜從簡單的機器到無所不能的程式
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318
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第 9 章
我們從型別系統獲得的任何資訊都不能盡信，而且在決定要相信多少的時候，也必須注
意它的極限。成功執行程式的靜態語意並不代表『這個程式一定能運作』，只是『這個
程式的確不會以特定的方式失敗』。能有這樣的自動化系統的確很棒，因為它可以告訴
我們程式沒有任何可能的臭蟲或錯誤，但正如我們在第 8 章所看到的，事情偏偏就是那
麼不巧。
應用
本章描繪了抽象解譯的基本概念（使用低廉的近似來學習昂貴運算的行為），並示範了
簡單的型別系統，作為近似對分析程式是如何有用的範例。
我們對抽象解譯的討論相當非正式。嚴格來說，抽象解譯是一種正式且正規的數學技
術，在這種技術裡將相同語言的不同語意，透過將一組具體的值轉換成抽象的值（反之
亦然）的函數相互連接，進而能以具體的值來瞭解抽象程式的結果和特性。
這種技術最知名的業界應用是 Astrée 靜態分析儀（
http://www.astree.ens.fr/
），它使用抽
象解譯來自動查驗 C 程式沒有諸如除以零、陣列索引超越邊界、整數溢位等執行階段
錯誤。Astrée 已經用在驗證空中巴士 A340 和 A380 飛機的飛行控制軟體，以及運補到
國際太空站的
Jules Verne
ATV-001 飛行任務的自動對接軟體。抽象解譯顧及萊斯定理
的方式，就是提供安全的近似，而非肯定的答案，所以 Astrée 回報的執行階段錯誤，
實際上可能不存在（誤警 [
false alarm
]）；實際上，它的抽象體精確度在驗證 A340 軟體
時，已足以避免任何誤警。
以 SIMPLE ...
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