BTEST Function Explained – FORTRAN

The btest operation checks whether a specific bit in a binary representation of an integer is set or not.

When we say that a “number is set” in the context of the btest operation, it means that a specific bit in the binary representation of the number has a value of 1 (or “on”).

Conversely, if the bit is not set, it means that the bit has a value of 0 (or “off”).

 

Syntax

RESULT = BTEST(I, POS)

 

The btest function takes two arguments:

1. i (integer, intent(in)): This is the number in which you want to test a specific bit. It is declared as an integer and marked as intent(in) to indicate that it is an input argument.
2. pos (integer, intent(in)): This is the position of the bit you want to test within the binary representation of the number i. It is declared as an integer and marked as intent(in) to indicate that it is an input argument.

The btest function returns a logical value, indicating whether the specified bit is set or not. If the bit is set, the function returns .true. (logical true), and if the bit is not set, it returns .false. (logical false).

Example Program that Demonstrates the btest operation in Fortran

program BTestExample
    implicit none
    
    integer :: num, bit
    logical :: result
    
    ! Prompt the user for input
    write(*,*) "Enter a number:"
    read(*,*) num
    
    write(*,*) "Enter the bit position (0-31):"
    read(*,*) bit
    
    ! Perform the btest operation
    result = btest(num, bit)
    
    ! Display the result
    if (result) then
        write(*,*) "Bit", bit, "is set in", num
    else
        write(*,*) "Bit", bit, "is not set in", num
    end if
    
end program BTestExample