Hardware Synthesis from C Programs with Estimation of Bit Length of Variables

Osamu OGAWA  Kazuyoshi TAKAGI  Yasufumi ITOH  Shinji KIMURA  Katsumasa WATANABE  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E82-A   No.11   pp.2338-2346
Publication Date: 1999/11/25
Online ISSN: 
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on VLSI Design and CAD Algorithms)
high-level synthesis,  hardware/software codesign,  VHDL,  C language,  compiler,  

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In the hardware synthesis methods with high level languages such as C language, optimization quality of the compilers has a great influence on the area and speed of the synthesized circuits. Among hardware-oriented optimization methods required in such compilers, minimization of the bit length of the data-paths is one of the most important issues. In this paper, we propose an estimation algorithm of the necessary bit length of variables for this aim. The algorithm analyzes the control/data-flow graph translated from C programs and decides the bit length of each variable. On several experiments, the bit length of variables can be reduced by half with respect to the declared length. This method is effective not only for reducing the circuit area but also for reducing the delay of the operation units such as adders.