pow and sqrt timing in fortran

pow_timing.f90

!  gfortran -O3 pow_timing.f90 -o pow_timing.x -mcmodel=medium
!-----------------------------------------------------------------------
!Main program test
!-----------------------------------------------------------------------
program  test
   implicit none
   integer, parameter :: dp = kind(1.d0)
   integer :: i
   integer, parameter :: s = 100000000
   real(dp) :: a
   real(dp), dimension(s) :: b1,b2,b3,b4,b5,b6,b7
   real(dp), dimension(2) :: time
   character(len=11):: fmt = '(A30,F12.6)'

   call cpu_time (time(1))
   do i = 1, s
      a = real(i,dp)
      b1(i) = a*a
   enddo
   call cpu_time (time(2))
   write(*,fmt) "a*a elapsed time = ", time(2)-time(1)

   call cpu_time (time(1))
   do i = 1, s
      a = real(i,dp)
      b2(i) = a**2
   enddo
   call cpu_time (time(2))
   write(*,fmt) "a**2 elapsed time = ", time(2)-time(1)

   call cpu_time (time(1))
   do i = 1, s
      a = real(i,dp)
      b3(i) = a**2.0
   enddo
   call cpu_time (time(2))
   write(*,fmt) "a**2.0 elapsed time = ", time(2)-time(1)

   call cpu_time (time(1))
   do i = 1, s
      a = real(i,dp)
      b4(i) = a**2.0_dp
   enddo
   call cpu_time (time(2))
   write(*,fmt) "a**2.0_dp elapsed time = ", time(2)-time(1)

   call cpu_time (time(1))
   do i = 1, s
      a = real(i,dp)
      b5(i) = sqrt(a)
   enddo
   call cpu_time (time(2))
   write(*,fmt) "sqrt(a) elapsed time = ", time(2)-time(1)

   call cpu_time (time(1))
   do i = 1, s
      a = real(i,dp)
      b6(i) = a**0.5
   enddo
   call cpu_time (time(2))
   write(*,fmt) "a**0.5 elapsed time = ", time(2)-time(1)

   call cpu_time (time(1))
   do i = 1, s
      a = real(i,dp)
      b7(i) = a**0.5_dp
   enddo
   call cpu_time (time(2))
   write(*,fmt) "a**0.5_dp elapsed time = ", time(2)-time(1)

   ! to force bx loops computation
   do i = 1, s
      if(b1(i) /= b2(i)) stop "error"
      if(b1(i) /= b3(i)) stop "error"
      if(b1(i) /= b4(i)) stop "error"
      if(b5(i) /= b6(i)) stop "error"
      if(b5(i) /= b7(i)) stop "error"
   enddo

end program test

gfortran 6.2.1 20160830

./pow_timing.x

       a*a elapsed time =     0.144000
      a**2 elapsed time =     0.132000
    a**2.0 elapsed time =     0.128000
 a**2.0_dp elapsed time =     0.128000
   sqrt(a) elapsed time =     0.784000
    a**0.5 elapsed time =     7.656000
 a**0.5_dp elapsed time =     7.716000

ifort (IFORT) 17.0.0 20160721

./pow_timing.x

       a*a elapsed time =     0.152000
      a**2 elapsed time =     0.136000
    a**2.0 elapsed time =     0.132000
 a**2.0_dp elapsed time =     0.136000
   sqrt(a) elapsed time =     0.412000
    a**0.5 elapsed time =     0.416000
 a**0.5_dp elapsed time =     0.416000