Bit matrix compression is a highly relevant operation in computer arithmetic. Essentially being a multi-operand addition, it is the key operation behind fast multiplication and many higher-level operations such as multiply-accumulate, the computation of the dot product or the implementation of FIR filters. Compressor implementations have been constantly evolving for greater efficiency both in general and in the context of concrete applications or specific implementation technologies. This paper is building on this history and describes a generic implementation of a bit matrix compressor for Xilinx FPGAs, which does not require a generator tool. It contributes FPGA-oriented metrics for the evaluation of elementary parallel bit counters, a systematic analysis and partial decomposition of previously proposed counters and a fully implemented construction heuristic with a flexible compression target matching the device capabilities. The generic implementation is agnostic of the aspect ratio of the input matrix and can be used for multiplication the same way as it can be for single-column population count operations.
The scheduling of counters to build a compressor depends naturally on the selection of available modules. It is the backing technology that defines which counters can be implemented most efficiently. A discussion of the choices for ASICs was composed by Verma and Ienne @cite_11 . FPGA-targeted counters have been most prominently proposed by Parandeh- @cite_8 @cite_12 @cite_5 as well as Kumm and Zipf @cite_7 @cite_6 . As this paper focuses on the construction of compressors within a modern Xilinx FPGA fabric, it will heavily build on the work of these latter two groups.
@cite_7 @cite_8 @cite_6 @cite_5 @cite_12 @cite_11
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FPGA performance is currently lacking for arithmetic circuits. Large sums of k > 2 integer values is a computationally intensive operation in applications such as digital signal and video processing. In ASIC design, compressor trees, such as Wallace and Dadda trees, are used for parallel accumulation; however, the LUT structure and fast carry-chains employed by modern FPGAs favor trees of carry-propagate adders (CPAs), which are a poor choice for ASIC design. This paper presents the first method to successfully synthesize compressor trees on LUT-based FPGAs. In particular, we have found that generalized parallel counters (GPCs) map quite well to LUTs on FPGAs; a heuristic, presented within, constructs a compressor tree from a library of GPCs that can efficiently be implemented on the target FPGA. Compared to the ternary adder trees produced by commercial synthesis tools, our heuristic reduces the combinational delay by 27.5 , on average, within a tolerable average area increase of 5.7 . Compressor trees offer an effective realization of the multiple input addition needed by many arithmetic operations. However, mapping the commonly used carry save adders (CSA) of classical compressor trees to FPGAs suffers from a poor resource utilization. This can be enhanced by using generalized performance counters (GPCs). Prior work has shown that high efficient GPCs can be constructed by exploiting the low-level structure of the FPGA. However, due to their irregular shape, the selection of those is not straight forward. Furthermore, the compressor tree has to be pipelined to achieve the potential FPGA performance. Then, a selection between registered GPCs or flip-flops has to be done to balance the pipeline. This work defines the pipelined compressor tree synthesis as an optimization problem and proposes a (resource) optimal method using integer linear programming (ILP). Besides that, two new GPC mappings with high efficiency are proposed for Xilinx FPGAs. Scholars are increasingly citing electronic “web references” which are not preserved in libraries or full text archives. WebCite is a new standard for citing web references. To “webcite” a document involves archiving the cited Web page through www.webcitation.org and citing the WebCite permalink instead of (or in addition to) the unstable live Web page. This journal has amended its “instructions for authors” accordingly, asking authors to archive cited Web pages before submitting a manuscript. Almost 200 other journals are already using the system. We discuss the rationale for WebCite, its technology, and how scholars, editors, and publishers can benefit from the service. Citing scholars initiate an archiving process of all cited Web references, ideally before they submit a manuscript. Authors of online documents and websites which are expected to be cited by others can ensure that their work is permanently available by creating an archived copy using WebCite and providing the citation information including the WebCite link on their Web document(s). Editors should ask their authors to cache all cited Web addresses (Uniform Resource Locators, or URLs) “prospectively” before submitting their manuscripts to their journal. Editors and publishers should also instruct their copyeditors to cache cited Web material if the author has not done so already. Finally, WebCite can process publisher submitted “citing articles” (submitted for example as eXtensible Markup Language [XML] documents) to automatically archive all cited Web pages shortly before or on publication. Finally, WebCite can act as a focussed crawler, caching retrospectively references of already published articles. Copyright issues are addressed by honouring respective Internet standards (robot exclusion files, no-cache and no-archive tags). Long-term preservation is ensured by agreements with libraries and digital preservation organizations. The resulting WebCite Index may also have applications for research assessment exercises, being able to measure the impact of Web services and published Web documents through access and Web citation metrics. @PARASPLIT [J Med Internet Res 2005;7(5):e60] A citing sentence is one that appears in a scientific article and cites previous work. Citing sentences have been studied and used in many applications. For example, they have been used in scientific paper summarization, automatic survey generation, paraphrase identification, and citation function classification. Citing sentences that cite multiple papers are common in scientific writing. This observation should be taken into consideration when using citing sentences in applications. For instance, when a citing sentence is used in a summary of a scientific paper, only the fragments of the sentence that are relevant to the summarized paper should be included in the summary. In this paper, we present and compare three different approaches for identifying the fragments of a citing sentence that are related to a given target reference. Our methods are: word classification, sequence labeling, and segment classification. Our experiments show that segment classification achieves the best results.