58 lines
1.5 KiB
FortranFixed
58 lines
1.5 KiB
FortranFixed
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!
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program twos_complement_demo
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implicit none
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integer :: x, tc
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integer :: nbits
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character(len=:), allocatable :: bits_x, bits_not, bits_tc
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! Prompt for input
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write(*,"(a)",advance="no") "Enter a positive integer (or any integer):"
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read *, x
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! Determine bit-width and convert to bit-strings
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nbits = bit_size(x)
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bits_x = to_bitstring(x)
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bits_not = to_bitstring(not(x))
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! Compute two's complement: flip all bits then add one
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tc = not(x) + 1
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bits_tc = to_bitstring(tc)
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! Display results
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10 format(a,t30,i0)
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20 format(a,i0,a,t30,a,/)
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30 format(a,t30,a)
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write(*,*)
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write(*,10) "Original integer:", x
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write(*,20) "Bit pattern (", nbits, " bits):", trim(bits_x)
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write(*,30) "After bitwise NOT: ", trim(bits_not)
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write(*,30) "Then add 1 --> two’s comp:", trim(bits_tc)
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write(*,*)
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write(*,10) "Two’s complement (decimal):", tc
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contains
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!------------------------------------------------------------
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! Convert an integer to a string of ‘0’ and ‘1’
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!------------------------------------------------------------
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function to_bitstring(val) result(str)
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integer, intent(in) :: val
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character(len=:), allocatable :: str
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integer :: n, i
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! Number of bits in this integer kind
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n = bit_size(val)
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allocate(character(len=n) :: str)
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do i = 1, n
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if (btest(val, n - i)) then
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str(i:i) = '1'
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else
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str(i:i) = '0'
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end if
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end do
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end function to_bitstring
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end program twos_complement_demo
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