sqrt() Implementation In C

Giving below the code to implement the library function sqrt() in C programming language:

float sqrt(float num)
{
    float guess, e, upperbound;
    guess = 1;
    e = 0.001;
    do 
    {
        upperbound = num / guess;
        guess = (upperbound + guess) / 2;
    } while (!(guess * guess >= num - e && 
               guess * guess <= num + e));
    return guess;
}
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