Skip to content

Implemented Fast Inverse Sqrt Method #3199

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Closed
ghost wants to merge 3 commits into from
Closed

Implemented Fast Inverse Sqrt Method #3199

Changes from all commits
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
b9e7d60
Implemented Fast Inverse Sqrt Method
Jul 23, 2022
da3de8d
Implemented Automated Tests
Jul 24, 2022
ecc04f2
Removed A Comment From The FastSqrt Class
Jul 24, 2022
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
71 changes: 71 additions & 0 deletions src/main/java/com/thealgorithms/maths/FastSqrt.java
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,71 @@
package com.thealgorithms.maths;

public class FastSqrt {

public static void main(String[] args){
float floatResult = 0f;
double doubleResult = 0d;
long start, mid, end; //Times to be benchmarked
start = System.currentTimeMillis();
for (float x = 1F; x < 4_000_000F; x += 0.25F) {
floatResult = inverseSqrt(x);
}
mid = System.currentTimeMillis();

for(double x = 1D; x < 4_000_000D; x += 0.25D){
doubleResult = inverseSqrt(x);
}
end = System.currentTimeMillis();

long controlled = mid - start;

long experimental = end - mid;

long percentageError = 100 * (controlled - experimental) / controlled;

System.out.println("Controlled Difference: " + controlled + "ms With result: " + floatResult);

System.out.println("Experimental Difference: " + experimental + "ms With result: " + doubleResult);

System.out.println("Method 2 of Inverse Square Root Was " + percentageError + "% faster than Method 1 of Inverse Square Root");
}

/**
* To better understand this algorithm, please refer to the following link: https://en.wikipedia.org/wiki/Fast_inverse_square_root
*/

/**
* Returns the inverse square root of the given number.
*
* @param number the number
* @return the inverse square root of the given number
*/
public static float inverseSqrt(float number) {
float x = number;
float xhalf = 0.5f * x;
int i = Float.floatToIntBits(x);
i = 0x5f3759df - (i >> 1);
x = Float.intBitsToFloat(i);
x = x * (1.5f - xhalf * x * x);
return x;
}

/**
* Returns the inverse square root of the given number in a more accurate way.
*
* @param number the number
* @return the inverse square root of the given number
*/
public static double inverseSqrt(double number) {
double x = number;
double xhalf = 0.5d * x;
long i = Double.doubleToLongBits(x);
i = 0x5fe6ec85e7de30daL - (i >> 1);
x = Double.longBitsToDouble(i);
for (int it = 0; it < 4; it++) {
x = x * (1.5d - xhalf * x * x);
}
x *= number;
return x;
}
}