HDU1141 Factstone Benchmark（数学）

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本文探讨了Amtel公司发布的计算机芯片技术发展，通过Factstone基准测试衡量其芯片性能，涉及从4位到128位的演进路径。

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Factstone Benchmark

Time Limit: 10000/5000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 1951 Accepted Submission(s): 1078

Problem Description

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

Sample Output

3
8

Source

University of Waterloo Local Contest 2005.09.24

题意：计算机芯片的bit每年都不一样，求一个数n使得n!<=2^bit时n的最大值。

思路：换成log计算log(n!) = log(n) + log(n-1) + ...... + log(1);

#include <stdio.h>
#include <math.h>
int main()
{
    int n, bit, i;
    while(scanf("%d", &n) != EOF){
        if(!n) break;
        bit = (n - 1960) / 10 + 2;
        bit = 1<<bit;
        double b = 1.0 * bit * log(2.0), s = 0;
        for(i = 1;;i++){
            s += log((double)i);
            if(s > b){
                printf("%d\n", i - 1);
                break;
            }
        }
    }
}