问题 单项选择题

已知两个浮点数,阶码为3位二进制数,尾数为5位二进制数,均用补码表示。

[X]=0.1101×2001,[y]=1.0111×2011

则两个数的和[x+y]= (1) ,并说明规格化数的要求是 (2)

(2)处填()。

A.阶码之值在阶数可表示的范围内

B.尾数之值在尾数可表示的范围内

C.结果尾数之绝对值≥

D.尾数之最高数值位=1

答案

参考答案:C

解析:

浮点数[x]+[y]=[x+y]

[x]=0.1101×2001

[y]=1.0110×2011

浮点加法第1步必须对阶求阶差:

△E=Ex-Ey=001-011=[001]+[-011]=110 即-2

x为小阶的数,x的阶应取大阶阶码:

[*]

第2步 尾数相加[*]

(Mz)=00.001101+11.0110=11.100101,Ez=011

第3步 规格化,规格化要求结果尾数的绝对值≥[*],现在尾数和的最高数值位为非有效位,绝对值<[*],需左规1位,阶码减1,即:

[*]

第4步 舍入,采用恒置1法。将最末位的1舍去(只能取4位尾数的值),再将尾数末位变成1,[*]

第5步 测溢出。浮点数判断溢出,主要看结果的阶码是否超出了阶码能表示的范围。

浮点数的阶码为3位补码,最大值是+3,最小值是斗,现在结果的阶码为+2,在阶码允许范围之内,所以浮点数不溢出。

阅读理解

Disposing(处理) of waste has been a problem since humans started producing it. As more and more people choose to live close together in cities, the waste-disposal problem becomes increasingly difficult.

During the eighteenth century, it was usual for several neighboring towns to get together to select a faraway spot as a dumpsite. Residents or trash haulers(垃圾托运者) would transport household rubbish, rotted wood, and old possessions to the site. Periodically(定期的) some of the trash was burned and the rest was buried. The unpleasant sights and smells caused no problem because nobody lived close by.

Factories, mills, and other industrial sites also had waste to be disposed of. Those located on rivers often just dumped the unwanted remains into the water. Others built huge burners with chimneys to deal with the problem.

Several facts make these choices unacceptable to modern society. The first problem is space. Dumps, which are now called landfills, are most needed in heavily populated areas. Such areas rarely have empty land suitable for this purpose. Property is either too expensive or too close to residential(住宅区的)neighborhoods. Long-distance trash hauling has been a common practice, but once farm areas are refusing to accept rubbish from elsewhere, cheap land within trucking distance of major city areas is almost nonexistent.

Awareness of pollution dangers has resulted in more strict rules of waste disposal. Pollution of rivers, ground water, land and air is a price people can no longer pay to get rid of waste. The amount of waste, however, continues to grow.

Recycling efforts have become commonplace, and many towns require their people to take part. Even the most efficient recycling programs, however, can hope to deal with only about 50 percent of a city's reusable waste.

小题1:The most suitable title for this passage would be ______.

A.Places for Disposing Waste

B.Waste Pollution Dangers

C.Ways of Getting Rid of Waste

D.Waste Disposal Problem小题2:During the 18th century, people disposed their waste in many ways EXCEPT for ______.

A.burying it

B.recycling it

C.burning it

D.throwing it into rivers小题3:What can be inferred from the fourth paragraph?

A.Farm areas accept waste from the city in modern society.

B.There is cheap land to bury waste in modem society.

C.It is difficult to find space to bury waste in modem society.

D.Ways to deal with waste in modem society stay the same.小题4: The main purpose of writing this article is to ________.

A.draw people's attention to waste management

B.warn people of the pollution dangers we are facing

C.call on people to take part in recycling programs

D.tell people a better way to get rid of the waste

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