Chapter 8: Floating-Point Anyone?

Overview

If you are interested in programming the FPU (floating-point unit) in assembly, you are either bored or deeply disturbed. My apologies to those few of you writing compilers or low-level operating system kernels who actually need to know how to do this! Then again, you may just be curious . Other books tend to stick this topic in the section beginning with "F," or somewhere buried in the back in an appendix, and maybe 1% of the readers actually even glance at it. Some people have been known to tape those pages together or just rip them out of their book (not my book) altogether. If C/C++ is good enough for you to handle your floating-point math, then just skip this section.

Wait! 

There are a couple items you REALLY NEED TO KNOW! Stuff not in the standard runtime C libraries. Something to make your code just a bit faster and better !

My gosh! You're still reading this? You must be indeed interested in floating-point math. So we will chat about a couple items but we are not going to go into very much detail only enough to take advantage of some enhanced functionality.

These are the three methods available to use for floating-point calculation: 3DNow!, SSE, and SSE2 packed instructions; run-time C libraries; and of course, ye old floating-point coprocessor known as the FPU (floating-point unit), for which most whom program it directly have a love/hate relationship. This book should help you get over that, at least in part.

It is strongly recommended that if you only have generic floating- point programming in mind (whether it be single-precision floating- point or double-precision floating-point), then just use your higher level language such as C/C++ instead. It will be much easier and any optimization will be merely that of intermixing general-purpose instructions with floating-point instructions.

Working with the SIMD instructions for floating-point support is much easier than working with the FPU, but the FPU has some helpful features. Fortunately, most of the hard work of directly programming the FPU has been done for you already and is available in libraries such as the runtime library for the C programming language. The FPU has so many nuances that it could take a several hundred-page book to understand all the feature sets, controls, exception handling, etc. This chapter is going to describe how floating-point works in general and paint some broad strokes as to how to use the FPU, especially the few instructions that can be of use but are not utilized by off-the-shelf libraries. If you indeed want to do in-depth programming I suggest you download the various technical manuals and application notes from the manufacturer.

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32.64-Bit 80X86 Assembly Language Architecture
32/64-Bit 80x86 Assembly Language Architecture
ISBN: 1598220020
EAN: 2147483647
Year: 2003
Pages: 191

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