DOWNLOAD MICHAEL ABRASH GRAPHICS PROGRAMMING BLACK BOOK

A programmer examines the requirements of an application, designs a solution at some level of abstraction, and then makes that design come alive in a code implementation. The Zen timer is an excellent tool for evaluating code performance over the entire spectrum of PC-compatible computers. Fans of the call it a bit processor. Let me put it this way: Much heroic programming ensued. Your job is to sequence those blocks so that they perform well. What was it like working with John Carmack on Quake?

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In order to perform any of the timing tests in this book, enter Listing 3. Development of the flexible mind is an obvious step.

There Ain't No Such Thing as the Fastest Code

Just like in college, the class topic doesn't matter when the instructor is a brilliant teacher. A final approach is to modify ZTimerReport to print the result to the auxiliary output via DOS function 4, and to then write and load a special device driver named AUXto which DOS function 4 output would automatically be directed.

In other words, the programming interface is 16 bits wide, but the hardware interface is only 8 bits wide, as shown in Figure 4. In my mind, the whole business of optimizing assemblers is a mixed blessing.

In the same chapter, Mr. I personally spent about 15 hours just driving back and forth between the two houses. One obvious effect of the 8-bit bus cycle-eater is that word-sized accesses to memory operands on the take 4 cycles longer than byte-sized accesses. First, that a single instruction that is intended to do a complex task is not necessarily faster than several instructions that together do the same thing.

These problems show up with any code that uses word-sized memory operands. In other words, the inherent nature of this application limits the performance improvement that can be obtained via assembly.

Graphics Programming Black Book Special Edition by Michael Abrash

Dynamic RAM refresh and wait states—our next topics—together form the lowest level at which the hardware of the PC affects code performance. In order to measure times longer than 54 ms, we must maintain not one but two timing components, the timer 0 count and the BIOS time-of-day count. A year or two later, after Wolfenstein-3D, I bumped into Michael in a virtual sense for the first time. However, using the registers is a rule of thumb, not a commandment. These changes convert the code to use C-style external label names and the small model C code segment.

The numbers are different, but the way the cycle-eater operates is exactly the same. To resolve this conflict, display adapters can tell the CPU to wait during bus accesses by inserting one or more wait states, as shown in Figure 4.

Graphics Programming Black Book Special Edition

However, in the PC, wait states most often occur when an instruction accesses a memory grzphics, so in fact the Execution Unit usually is stopped by wait states. There are a couple of interesting aspects to the last example.

Ignorance can also be responsible for considerable wasted effort. Let me put it this way: Believe it or not, a single REP MOVSW instruction can lose as much asword-sized memory accesses x 4 cycles, orcycles to the 8-bit bus cycle-eater!

If you do leave the PS2 equate at 1 in Listing 3. You will have to find your own path of learning, although I will start you on your way with this book.

There Ain't No Such Thing as the Fastest Code

Truth to tell, I didn't expect a three-times speedup; around two times was what I had in mind. LOOP, JCXZthe various accumulator-specific instructions, and even the string instructions in many circumstances no longer offer the advantages they did on the Someone rushes out and buys a gas heater, and at considerable risk to life and limb hooks it up to an abandoned but still live gas pipe that once fed a stove on the third floor. This chapter, adapted from my earlier book, Zen of Assembly Language located on the companion CD-ROM, goes right to the heart of my philosophy of optimization: You do indeed need tools to build a house, but any of many sets of tools will do.

So how did the entrants in this particular challenge stack up?

Nor is there any way to structure code gra;hics minimize the impact of DRAM refresh. There are four reasons that many programmers would give for not trying to improve on Listing 1. That means that you can, for example, multiply EBX by 5 with:.

By understanding the circumstances in which wait states can occur, you can avoid them when possible.