求阶乘与乘法分析

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#include <stdio.h>#include <math.h>long max(int a);  void ConvetToBinary(int v);void main(){int m,n;int max_value;int size_of_long=sizeof(long);int flag=1;max_value=pow(2.0,size_of_long*8-1)-1;printf("max_value = %d  (0X %08X)  ",max_value,max_value);printf("sizeof(long)=%d\n",size_of_long);for(m=0;m<=30;m++){n=max(m);if(n<=max_value&&(n>>31==0)&&flag){printf("%2d的阶层为 %11d  (0X %08X)  Right  ",m,n,n);ConvetToBinary(n);}else{flag=0;printf("------------------------------------------------\n");printf("%2d的阶层为 %11d  (0X %08X)  Wrong  ",m,n,n);ConvetToBinary(n);}}}long max(int a){if(a==0) return 1;else return a*max(a-1);}void ConvetToBinary(int v){ int nBits; int i; nBits=sizeof(int)<<3; for(i=nBits-1;i>=0;i--) {  printf("%d",(v>>i)&1);}printf("\n");}

x*17=x*16+x 即x左移4位再与x相加

01110111011101011000000000000000 |<-- 16的阶乘为x

01110111010110000000000000000000 |<-- 左移4位(x<<4)

11101110110011011000000000000000 |<-- +x 补码

转换为10进制（负数的补码等于其绝对值的原码各位取反再加1）：

11101110110011010111111111111111 |<-- -1

00010001001100101000000000000000 |<-- 取反(~)

即288522240(十进制) 添上符号即-288522240