6.11.173 sqrt Function

Calculates the square root of a double precision floating-point value.

Include

<math.h>

Prototype

double sqrt(double x);

Argument

x

a non-negative floating-point value

Return Value

Returns the non-negative square root of x.

Remarks

If x is less than 0, a domain error will occur and errno will be set to EDOM.

When targeting Cortex-M devices, MPLAB XC32 uses different algorithms for sqrt(), based on the optimization level selected. When level s optimizations (-Os) have been specified, square roots are performed using the Newton algorithm, which can produce smaller code. For all other optimization levels, the Kahan algorithm is used. The square root for some values might differ slightly based on the algorithm chosen, but in both cases, they should produce answers ±1 ulp (unit of least precision).

Example

See the notes at the beginning of this chapter or section for information on using printf() or scanf() (and other functions reading and writing the stdin or stdout streams) in the example code.

#include <math.h>
#include <stdio.h>
#include <errno.h>

int main(void)
{
  double x, y;

  errno = 0;
  x = 0.0;
  y = sqrt(x);
  if (errno)
    perror("Error");
  printf("The square root of %f is %f\n", x, y);

  errno = 0;
  x = 9.5;
  y = sqrt(x);
  if (errno)
    perror("Error");
  printf("The square root of %f is %f\n", x, y);

  errno = 0;
  x = -25.0;
  y = sqrt(x);
  if (errno)
    perror("Error");
  printf("The square root of %f is %f\n", x, y);
}

Example Output

The square root of 0.000000 is 0.000000
The square root of 9.500000 is 3.082207
Error: domain error
The square root of -25.000000 is nan