Irresistibles bagues de perles: Volume 3 by Meriem Varone

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By Meriem Varone

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1 nanoseconds. (A nanosecond is one-billionth of a second, and is abbreviated ns). Listing 2-1 shows 8253-based timer software, consisting of three subroutines: ZTimerOn, ZTimerOff, and ZTimerReport. " THE ZEN TIMER IS A MEANS, NOT AN END We're going to spend the rest of this chapter seeing what the Zen timer can do, Abrash/Zen: Chapter 2/ examining how it works, and learning how to use it. The Zen timer will be our primary tool for the remainder of The Zen of Assembly Language, so it's essential that you learn what the Zen timer can do and how to use it.

THE ZEN TIMER One key to mastering the Zen of assembler is clearly a tool with which to measure code performance. The most accurate way to measure performance is with expensive hardware, but reasonable measurements at no cost can be made with the PC's 8253 timer chip, which counts at a rate of slightly over 1,000,000 times per second. The 8253 can be started at the beginning of a block of code of interest and stopped at the end of that code, with the resulting count indicating how long the code took to execute with an accuracy of about 1 microsecond.

The programmer's mistake was one of context. While his solution seemed optimal by the standards of the C environment he was programming in, it was considerably less ideal when applied to the PC, the environment in which the code actually had to run. While humanoriented abstractions such as high-level languages and system software have their virtues--most notably the ability to mask the complexities of processors and hardware--speed is not necessarily among those virtues. Abrash/Zen: Chapter 3/ We certainly don't want to make the same mistake, so we'll begin our search for knowledge by establishing a context for assembler programming, a usable framework within which to work for the remainder of this book.

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