开根号几种写法

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>
#include <xmmintrin.h>

#include "util.h"

#define eps 0.00001

float SqrtByBisection(float n)
{
if(n<0)
{
return -1.0;
}
else
{
float low,up,mid,last;
low=0,up=(n<1?1:n);
mid=(low+up)/2;

do
{
if(mid*mid>n)
up=mid;
else
low=mid;

last=mid;
mid=(up+low)/2;
//printf("mid is %f,last is %f\n",mid,last);

}while(fabsf(mid-last) > eps);

return mid;
}
}

float SqrtByNewton(float x)
{
//int temp = (((*(int *)&x)&0xff7fffff)>>1)+(64<<23);
int temp=0x1fc00000+((*(int *)&x)>>1);
//int temp=0x1fbd1e2d+((*(int *)&x)>>1);
float val=*(float*)&temp;
//float val=x;

val =(val + x/val) / 2;
val =(val + x/val) / 2;
val =(val + x/val) / 2;

return val;
}

float SqrtByCarmack( float number )
{
int i;
float x2, y,last;
const float threehalfs = 1.5F;

x2 = number * 0.5F;
y  = number;
i  = * ( int * ) &y;                       // evil floating point bit level hacking
i  = 0x5f375a86 - ( i >> 1 );               // what the fuck?
y  = * ( float * ) &i;

printf("init is %f\n",y);

y  = y * ( threehalfs - ( x2 * y * y ) );   // 1st iteration
y  = y * ( threehalfs - ( x2 * y * y ) );   // 2nd iteration, this can be removed
y  = y * ( threehalfs - ( x2 * y * y ) );   // 2nd iteration, this can be removed

return number*y;
}

float SqrtByRSQRTSS(float a)
{
float b=a;
__m128 in = _mm_load_ss(&b);
__m128 out = _mm_rsqrt_ss(in);
_mm_store_ss(&b, out);

return a*b;
}

float SqrtBySQRTSS(float a)
{
__m128 in = _mm_load_ss(&a);
__m128 out = _mm_sqrt_ss(in);
_mm_store_ss(&a, out);

return a;
}

int main()
{
clock_t start,end;
struct timeval start1,finish1;
float s;
int i;
FILE* fp;

gettimeofday(&start1,NULL);
for(i=1;i<3000001;i++)
{
s=SqrtByBisection(i);
}
gettimeofday(&finish1,NULL);
printf("bisection value:%f,run time of bisection is %f\n",s,difftime_ms(finish1,start1));//

gettimeofday(&start1,NULL);
for(i=1;i<3000001;i++)
{
s=SqrtByNewton(i);
}
gettimeofday(&finish1,NULL);
printf("newton value:%f,run time of newton is %f\n",s,difftime_ms(finish1,start1));//

gettimeofday(&start1,NULL);
//for(i=1;i<3000001;i++)
{
s=SqrtByCarmack(3000001);
}
gettimeofday(&finish1,NULL);
printf("carmack value:%f,run time of carmack is %f\n",s,difftime_ms(finish1,start1));

gettimeofday(&start1,NULL);
for(i=1;i<3000001;i++)
{
s=sqrtf(i);
}
gettimeofday(&finish1,NULL);
printf("system value:%f,run time of system is %f\n",s,difftime_ms(finish1,start1));

gettimeofday(&start1,NULL);
for(i=1;i<3000001;i++)
{
s=SqrtByRSQRTSS(i);
}
gettimeofday(&finish1,NULL);
printf("RSQRTSS value:%f,run time of RSQRTSS is %f\n",s,difftime_ms(finish1,start1));

gettimeofday(&start1,NULL);
for(i=1;i<3000001;i++)
{
s=SqrtBySQRTSS(i);
}
gettimeofday(&finish1,NULL);
printf("SQRTSS value:%f,run time of SQRTSS is %f\n",s,difftime_ms(finish1,start1));

}