Garbage Collector Verification for Proof-Carrying Code

We present the verification of the machine-level implementation of a conservative variant of the standard mark- sweep garbage collector in a Hoare-style program logic.The specification of the collector is given on a machine-level memory model using separation logic,and is strong enough to preserve the safety property of any common mutator program.Our verification is fully implemented in the Coq proof assistant and can be packed immediately as foundational proof-carrying code package.Our work makes important attempt toward building fully certified production-quality garbage collectors.     

PCC技术在移动Agent系统安全中的应用初探

1 引言移动代码指可以在一台或多台远程主机上而不仅限于在源主机上运行的程序。从Java applet、ActiveX程序直至90年代中期提出的移动Agent技术均属于这一范畴。其思想是化远程调用为本地执行,从而具有减少网络负载、避免网络延时、动态适应、异步自主执行、支持异构体系、健壮性和容错性等优点。可以说,代码的可移动性是对传统非分布环境中可编程性的很大扩展。然而,高效与灵活的增长并非不无代价:分布式环境中代码的移动使安全威胁增多,安全保护更为复杂,安全课题也更为重要。     

实现谱峰自动识别的句法方法

本文描述一种用于自动识别数字谱数据序列中的谱峰的句法方法.为便于谱峰识别,先将谱数据序列编码为谱峰描述语句,然后用一种谱峰识别自动机将其中的谱峰一一选出.文中详细说明了产生谱峰描述语言的谱峰文法和识别谱峰的谱峰识别自动机,同时给出了实验结果.     

基于神经网络的网络验证码识别研究

本文首先介绍了神经网络的基本思想,提出了一种基于神经网络的网络验证码的识别方法,并利用开源的神经网络包JOONE用Java技术实现了验证码识别软件。最后通过训练样本对其进行了实验分析,取得了较高的识别率。     

基于HNC理论的句法结构歧义消解

歧义消解是自然语言理解和处理所面对的核心问题。基于词组和短语的消歧不能保证消歧结果的正确,歧义的成功消解基于对语境或上下文(context)的正确理解。HNC理论采取的概念基元化、层次化、网络化、形式化策略以及在此基础上建立的句类和句式体系,为自然语言的歧义消解提供了最大的可能。基于HNC理论的歧义消解的总体原则是,以语句为基础,充分利用语句语境提供的句类知识,采取宏观消歧与微观消歧相结合的策略。对于经典句法歧义结构V+NP1+的+NP2,本文描述了其三重性歧义性质,并提出了三条准则和十个推论以实现对其歧义的消解。     

量子纠错码的一个统一构造方法

在量子通信和量子计算中,量子纠错码起着至关重要的作用。人们已经利用Hamming码、BCH码、Reed-Solomon码等各种循环码、常循环码、准循环码来构造量子纠错码。利用准缠绕码将这些构造方法统一起来,给出了准缠绕码包含其对偶码的充分必要条件及准缠绕码的一个新构造方法,并且利用准缠绕码构造了新的量子纠错码。     

A Concept Formation Based Approach to Object Identification in Procedural Code

Legacy software systems present a high level of entropy combined with imprecise documentation. This makes their maintenance more difficult, more time consuming, and costlier. In order to address these issues, many organizations have been migrating their legacy systems to emerging technologies. In this paper, we describe a computer-supported approach aimed at supporting the migration of procedural software systems to the object-oriented (OO) technology. Our approach is based on the automatic formation of concepts, and uses information extracted directly from code to identify objects. The approach tends, thus, to minimize the need for domain application experts.     

面向代码审查的细粒度代码变更溯源方法

代码审查是现代软件分布式并行开发过程中的重要机制. 在代码评审时, 帮助代码评审者快速查看某一段源代码的演化过程, 可以让评审者快速理解此段代码变更的原因和必要性, 从而有效提升代码评审的效率与质量. 现有工作虽然提供了一些类似的代码提交历史回溯方法及对应工具, 但缺乏从历史数据中进一步提取辅助代码评审相关辅助信息的能力. 为此, 提出一个面向代码评审的细粒度代码变更溯源方法C2Tracker. 给定一段方法(函数)级别的细粒度代码变更, C2Tracker能够自动追溯到历史开发过程中修改该段代码相关的代码提交, 并在此基础上进一步挖掘其中与该段代码频繁共现修改的代码元素以及相关的变更片段, 辅助代码评审者对当前代码变更的理解与决策. 在10个著名开源项目的数据集下进行实验验证. 实验结果表明, C2Tracker在追溯历史提交的准确率上达到97%, 在挖掘频繁共现代码元素任务上的准确率达到95%, 在追溯相关代码变更片段任务上的准确率达到97%; 相比现有评审方式, C2Tracker在具体案例的代码评审效率和质量上均有较大提升, 在绝大多数的代码评审案例中被评审者认为能提供“明显帮助”或“很大帮助”.     

基于图嵌入的软件项目源代码检索方法

源代码检索是软件工程领域的一项重要研究问题,其主要任务是检索和复用软件项目API（application program interface,应用程序接口）.随着软件项目的规模越来越大、越来越复杂,当前,源代码检索一方面需要提高基于自然语言API查询的准确性,另一方面需要定位和展示目标API及其相关代码之间的关联,以更好地辅助用户理解API的实现逻辑和使用场景.为此,提出一种基于图嵌入的软件项目源代码检索方法.该方法能够基于软件项目源代码自动构建其代码结构图,并通过图嵌入对源代码进行信息表示.在此基础上,用户可以输入自然语言问题、检索并返回相关的API及其关联信息构成的连通代码子图,从而提高API检索和复用的效率.在以开源项目Apache Lucene和POI为例的检索实验中,该方法检索结果的F1值比现有基于最短路径的方法提高了10%,同时显著缩短了平均响应时间.     

Constraint-Defined Manifolds: a Legacy Code Approach to Low-Dimensional Computation

If the dynamics of an evolutionary differential equation system possess a low-dimensional, attracting, slow manifold, there are many advantages to using this manifold to perform computations for long term dynamics, locating features such as stationary points, limit cycles, or bifurcations. Approximating the slow manifold, however, may be computationally as challenging as the original problem. If the system is defined by a legacy simulation code or a microscopic simulator, it may be impossible to perform the manipulations needed to directly approximate the slow manifold. In this paper we demonstrate that with the knowledge only of a set of “slow” variables that can be used to parameterize the slow manifold, we can conveniently compute, using a legacy simulator, on a nearby manifold. Forward and reverse integration, as well as the location of fixed points are illustrated for a discretization of the Chafee-Infante PDE for parameter values for which an Inertial Manifold is known to exist, and can be used to validate the computational results     

一种新型Turbo码交织器设计方法

Turbo码由于其优越的性能已经被IMT-2000确定为首选编码方案。交织器在Turbo码中起着关键性的作用。该文利用分组交织器和随机交织器的优点,设计出一种新型Turbo码交织器(分组随机交织器)。仿真结果显示,在信噪比较低、帧长较短的条件下,这种新型交织器具有比分组交织器和随机交织器更好的性能。     

一种基于Hilbert排列码的GIS空间索引方法

分析了基于栅格格网的索引数据结构在空间查询中的重要地位,讨论了基于多维数据一维映射的空间排列的优点,对Morton码、Gray码、Hibert码和Sierpinsky码的空间聚类特征进行了分析和比较,得出了Hilbert码在空间查询中效率最高的结论,考虑到基于特征的GIS数据模型的特点,兼顾内存索引与磁盘索引,提出了基于Hilbert空间排列的点特征二叉平衡排序树动态索引结构和基于角点回溯的线特征索引结构,并对其在GIS空间查询中的应用方法进行了论述。     

Structurally-Enhanced Approach for Automatic Code Transformation

In software development, developers often need to change or update lost of similar codes. How to perform code transformation automatically has become a research hotspot in software engineering. An effective way is extracting the modification pattern from a set of similar code changes and applying it to automatic code transformation. In the related work, deep-learning-based approaches have achieved much progress, but they suffer from the problem of significant long-term dependency between the code. To address this challenge, an automatic code transformation method is proposed, namely ExpTrans. Based on the graph-based representations of code changes, ExpTrans is enhanced with the structural information of code. It labels the dependency between variables in code parsing and adopts the graph convolutional network and Transformer structure to capture the long-term dependency between the code. ExpTrans is first compared with existing learning-based approaches to evaluate its effectiveness; the results show that ExpTrans gains 11.8%--30.8% precision increment. Then, it is compared with rule-based approaches and the results demonstrate that ExpTrans significantly improves the correct rate of the modified instances.     

A Fully Syntactic AC-RPO

We present the first fully syntactic (i.e., non-interpretation-based) AC-compatible recursive path ordering (RPO). It is simple, and hence easy to implement, and its behaviour is intuitive as in the standard RPO. The ordering is AC-total and defined uniformly for both ground and nonground terms, as well as for partial precedences. More important, it is the first one that can deal incrementally with partial precedences, an aspect that is essential, together with its intuitive behaviour, for interactive applications such as Knuth–Bendix completion.     

利用句法短语改善统计机器翻译性能

短语表是基于短语的统计机器翻译系统的一个核心组成部分,基于启发式方法抽取到的短语表受单词对齐错误和未对齐词的影响严重,同时抽取到的短语也并非句法意义上的短语。该文提出一种基于EM(Expectation-maximization)算法的双语句法短语抽取方法来抽取双语句法短语,此方法可以通过不断迭代的方式使各参数值达到最优。通过加入双语句法短语、增加新特征、重新训练三种不同的方法,将获得的双语句法短语与基于短语的统计机器翻译方法结合以提高统计机器翻译系统的性能。结果表明: 三种方法都不同程度提高了译文的BLEU(BiLingual Evaluation Understudy)值,其中增加新特征方法提高了0.64个点。     

HoneyGadget: A Deception Based Approach for Detecting Code Reuse Attacks

Information Systems Frontiers - Code reuse attacks such as Return-Oriented Programming (ROP) and Jump-Oriented Programming (JOP) are the prevalent attack techniques which reuse code snippets named...     

二维条码的识别方法

以QR矩阵码为例,介绍一种实用的二维条码识别算法。首先探讨了二维条码的定位与分割算法,利用Hough变换与Sobel边缘检测把条码图像从原始采集的图像中有效地分割出来;然后分析了条码图像经过光学系统的噪声模型,提出了一种计算点扩展函数标准方差的算法;采用Flourier变换自适应地选取阈值去除噪声导致的无效边界,从而得到条码的基本模块。实验结果表明,该算法具有很好的抗噪性,提高了二维条码的识别率。     

一种结构信息增强的代码修改自动转换方法

在开发过程中,开发人员在进行缺陷修复、版本更新时,常常需要修改多处相似的代码.如何进行自动代码修改已成为软件工程领域的热点研究问题.一种行之有效的方式是:给定一组代码修改示例,通过抽取其中的代码修改模式,辅助相似代码进行自动转换.在现有工作中,基于深度学习的方法取得了一定进展,但在捕获代码间的长程信息依赖关系时,效果不...