The first English passage

 Reading the old code makes me suffering a lot because of my poor english.  I missed some sentences While knowing every word .Everything's hard in the beginning. More practices make it easy.Come on!
A Programmer's Perspective Most books on systems—computer architecture, compilers, operating systems, and networking—are written as if the reader were going to design and implement such a system. We call this the “builder's persepective.” We believe that students should first learn about systems in terms of how they affect the behavior and performance of their programs—a “programmer's perspective.” Here are some simple examples showing the contrast between the two perspectives: Computer Arithmetic Logic design and computer architecture courses describe how to implement fast and efficient arithmetic circuits. For programmers, what really matters is how the finite word sizes used to represent integer and floating point data determines what values can be represented and the behavior of different operations. For example, consider the following C function to compute the squares of 5, 50, 500, 5000, 50000, 500000, and 5000000: void show_squares() { int x; for (x = 5; x <= 5000000; x*=10) printf("x = %d x^2 = %d\n", x, x*x); } When compiled on most machines, this program produces the following values: x = 5 x^2 = 25 x = 50 x^2 = 2500 x = 500 x^2 = 250000 x = 5000 x^2 = 25000000 x = 50000 x^2 = -1794967296 x = 500000 x^2 = 891896832 x = 5000000 x^2 = -1004630016 The first four values are exactly what one would expect, but the last three seem quite peculiar. We even see that the “square” of a number can be negative! Since data type int uses a 32-bit, two's complement representation on most machines, programs cannot represent the value 2.5 X 109 as an int. In Chapter 2 we cover the two's complement number system used to represent integers on most computers and its mathematical properties. We also cover the IEEE floating point representation from a programmer's perspective.
08-25
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