Soft-SIMD – Exploiting Subword Parallelism Using Source Code Transformations

SIMD instructions are used to speed up multimedia ap-plications in high performance embedded computing. Ven-dors often use proprietary platforms which are incompati-ble with others. Therefore, porting software is a very com-plex and time consuming task. Moreover, lots of existing embedded processors do not have SIMD extensions at all. But they do provide a wide data path which is 32-bit or wider. Usually, multimedia applications work on short data types of 8 or 16-bit. Thus, only the lower bits of the data path are used and therefore only a fraction of the available computing power is exploited for such algorithms. This paper discusses the possibility to make use of the upper bits of the data path by emulating true SIMD instructions. These instructions are implemented purely in software us-ing a high level language such as C. Therefore, the applica-tion can be modified by making use of source code transfor-mations which are inherently portable. The benefit of this approach is that the computing resources are used more ef-ficiently without compromising the portability of the code. Experiments have shown that a significant speedup can be obtained by this approach.