Can't implement square root systemcall in linux kernel

Question

I need to implement this function as a systemcall:

asmlinkage ​ long​​ sys_sqrt (​ float​ x);

Where the function gonna print the square root of n to the kernel log. I'm using kernel version 4.13 on 64bit virtual box.

I'm trying to implement the sqrt by using this technique

#include <linux/kernel.h>
#define SQRT_MAGIC_F 0x5f3759df 
 asmlinkage ​long​​ sys_sqrt(​float​ x);
{
  const float xhalf = 0.5f*x;

  union // get bits for floating value
  {
    float x;
    int i;
  } u;
  u.x = x;
  u.i = SQRT_MAGIC_F - (u.i >> 1);
  printk ("%f", (x*u.x*(1.5f - xhalf*u.x*u.x));
  return 0;
} 

This leads the compiler telling me "error: SSE register return with SSE disabled" on "printk ("%f", (x * u.x * (1.5f - xhalf * u.x * u.x));"

Another workaround I tried is separating the integer and the decimals like so

float ans = (x*u.x*(1.5f - xhalf*u.x*u.x);
int head = ans;
float tail_float = ans - head;
int tail = tail_float*10000;
printk ("%d.%03d", head,tail);

This leads the compiler telling me "error:SSE register return with SSE disabled" on "float ans = (x *u.x *(1.5f - xhalf * u.x* u.x);"

another thing i've tried is adding a kernel_fpu_begin & end between the function body but this leads "error: implicit declaration of function "kernel_fpu_begin"; did you mean "kernel_old_dev_t"

Any solution? Thank you so much.