弱问一个简单的问题

lulibing

最近正在学习verilog，想问一下为什么{random}%60产生的是0~59之间的数
也就是random加拼接运算符后产生的值就略去了负的部分呢？
期望有人解答，谢谢!~!~!~!

humann

You ask a very good question.

According IEEE 1364-2005 page 341:

The system function $random provides a mechanism for generating random numbers. The function returns
a new 32-bit random number each time it is called. The random number is a signed integer; it can be positive
or negative. For further information on probabilistic random number generators, see 17.9.2.
The seed argument controls the numbers that $random returns so that different seeds generate different
random streams. The seed argument shall be either a reg, an integer, or a time variable. The seed value
should be assigned to this variable prior to calling $random.
For example:
Example 1—Where b is greater than 0, the expression ($random % b) gives a number in the following
range: [(-b+1): (b-1)].

So I think your assumption is wrong.

lulibing

我是看到夏宇闻老师书上他是这么写的，因为我不是很明白，所以才问的。

eddsos

很简单，说明书错了：）

humann

好好干，你能成为一个优秀的工程师的.

[ 本帖最后由 humann 于 2009-2-24 03:09 编辑 ]

humann

夏宇闻 is right. I make a mistake.

The {} treats all parameter as unsigned  value and so products an  unsigned value too.

You can run the following test program in simulator.

You can try to remove {} to watch the different effect.


// test program
module top;      
   initial       repeat(80) #1 $display("%d ($random) mod 60  ->  %d", $random, {$random}%60);   
   initial       #100 $finish;           
endmodule

hermit2008

我的理解也是，{random}%相当于对正数的求%，

zhouhong

对这个系统函数，我还没有用过。不过现在学到了一些新的知识了。

fff000

恩，不错的问题