最快浮点数取绝对值

来源：互联网发布：大华onvif端口编辑：程序博客网时间：2024/05/16 07:52

做视频算法10多年，经常要算绝对值，整数的绝对值有快速算法，但浮点数的绝对值没看到有快速算法，经常不段发现，得到如下浮点数的快速算法：

快6倍多，

#include <Windows.h>#include <iostream>#include <stdio.h>#include <stdlib.h>#include <math.h>union funion{float fnum;BYTE  bnum[4];} ;float fabs_11(float x){return  (x < 0) ? -x : x;}void main(void){int iTime;float ret;union funion tmp1,tmp2;float  x =- 2110000.0001;iTime = GetTickCount();for(; x < 2210000.987;x+=0.3){tmp1.fnum = x;//printf("%f\t%2.2x%2.2x%2.2x%2.2x\n",tmp1.fnum,tmp1.bnum[3],tmp1.bnum[2],tmp1.bnum[1],tmp1.bnum[0]);//  printf("%f\t%2.2x%2.2x%2.2x%2.2x\n",tmp2.fnum,tmp2.bnum[3],tmp2.bnum[2],tmp2.bnum[1],tmp2.bnum[0]);tmp1.bnum[3] = tmp1.bnum[3]&0x7f;//printf("%f\t%2.2x%2.2x%2.2x%2.2x\n",tmp1.fnum,tmp1.bnum[3],tmp1.bnum[2],tmp1.bnum[1],tmp1.bnum[0]);//  printf("%f\t%2.2x%2.2x%2.2x%2.2x\n",tmp2.fnum,tmp2.bnum[3],tmp2.bnum[2],tmp2.bnum[1],tmp2.bnum[0]);}printf("gai  time = %d\n",GetTickCount() - iTime);iTime = GetTickCount();x =- 2110000.0001;for(; x < 2210000.987;x+=0.3){ fabs_11(x);}printf("old  time = %d\n",GetTickCount() - iTime);}

如果浮点数是double，将如何生成呢？

请大家先想想，后看答案。

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#include <Windows.h>#include <iostream>#include <stdio.h>#include <stdlib.h>#include <math.h>union funion{double fnum;BYTE  bnum[8];} ;double fabs_11(double x){return  (x < 0) ? -x : x;}void main(void){int iTime;double ret;union funion tmp1,tmp2;double  x =- 2110000.0001;iTime = GetTickCount();for(; x < 2210000.987;x+=0.3){tmp1.fnum = x;printf("%f\t%2.2x%2.2x%2.2x%2.2x\n",tmp1.fnum,tmp1.bnum[3],tmp1.bnum[2],tmp1.bnum[1],tmp1.bnum[0]);//  printf("%f\t%2.2x%2.2x%2.2x%2.2x\n",tmp2.fnum,tmp2.bnum[3],tmp2.bnum[2],tmp2.bnum[1],tmp2.bnum[0]);tmp1.bnum[7] = tmp1.bnum[7]&0x7f;printf("%f\t%2.2x%2.2x%2.2x%2.2x\n",tmp1.fnum,tmp1.bnum[3],tmp1.bnum[2],tmp1.bnum[1],tmp1.bnum[0]);//  printf("%f\t%2.2x%2.2x%2.2x%2.2x\n",tmp2.fnum,tmp2.bnum[3],tmp2.bnum[2],tmp2.bnum[1],tmp2.bnum[0]);}printf("gai  time = %d\n",GetTickCount() - iTime);iTime = GetTickCount();x =- 2110000.0001;for(; x < 2210000.987;x+=0.3){ fabs_11(x);}printf("old  time = %d\n",GetTickCount() - iTime);}