TOJ 1777.Factstone Benchmark（取对数）

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本文介绍了一种新的计算机性能评测标准——Factstone基准，并提供了解决方案。该基准定义为能在计算机字中表示的最大整数n的阶乘。文章通过数学方法解决了如何找到对应年份的Factstone评级的问题。

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题目链接：http://acm.tju.edu.cn/toj/showp1777.html

1777. Factstone Benchmark

Time Limit: 1.0 Seconds Memory Limit: 65536K
Total Runs: 692 Accepted Runs: 402

Amtel has announced that it will release a 128-bit computer chip by 2010, a 256-bit computer by 2020, and so on, continuing its strategy of doubling the word-size every ten years. (Amtel released a 64-bit computer in 2000, a 32-bit computer in 1990, a 16-bit computer in 1980, an 8-bit computer in 1970, and a 4-bit computer, its first, in 1960.)

Amtel will use a new benchmark - the Factstone - to advertise the vastly improved capacity of its new chips. The Factstone rating is defined to be the largest integer n such that n! can be represented as an unsigned integer in a computer word.

Given a year 1960 ≤ y ≤ 2160, what will be the Factstone rating of Amtel's most recently released chip?

There are several test cases. For each test case, there is one line of input containing y. A line containing 0 follows the last test case. For each test case, output a line giving the Factstone rating.

Sample Input

1960
1981
0

Sample Output

3
8

Source: Waterloo Local Contest Sep. 24, 2005

Submit List Runs Forum Statistics

题目链接：http://poj.org/problem?id=2661

利用：

2^n<1*2*3...m

n<log21+log22+log23.....然后换底公式

代码：

#include <stdio.h>
#include <cmath>
using namespace std;
int main(){
	int n,i;
	while(~scanf("%d",&n),n){
		double tmp=pow(2.0,((n-1960)/10+2));
		double sum=0;
		for(i=1;tmp>sum;i++)
			sum+=log(1.0*i)/log(2.0);
		printf("%d\n",i-2);
	}
}