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60 lines
2.1 KiB
Fortran
60 lines
2.1 KiB
Fortran
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module gf64math
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! Basic math in GF(64), for JT65 and QRA64
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implicit none
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integer :: gf64exp(0:62),gf64log(0:63)
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! gf64exp: GF(64) decimal representation, indexed by logarithm
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data gf64exp/ &
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1, 2, 4, 8, 16, 32, 3, 6, 12, 24, &
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48, 35, 5, 10, 20, 40, 19, 38, 15, 30, &
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60, 59, 53, 41, 17, 34, 7, 14, 28, 56, &
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51, 37, 9, 18, 36, 11, 22, 44, 27, 54, &
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47, 29, 58, 55, 45, 25, 50, 39, 13, 26, &
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52, 43, 21, 42, 23, 46, 31, 62, 63, 61, &
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57, 49, 33/
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! logarithms of GF(64) elements, indexed by decimal representation
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data gf64log/ &
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-1, 0, 1, 6, 2, 12, 7, 26, 3, 32, &
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13, 35, 8, 48, 27, 18, 4, 24, 33, 16, &
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14, 52, 36, 54, 9, 45, 49, 38, 28, 41, &
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19, 56, 5, 62, 25, 11, 34, 31, 17, 47, &
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15, 23, 53, 51, 37, 44, 55, 40, 10, 61, &
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46, 30, 50, 22, 39, 43, 29, 60, 42, 21, &
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20, 59, 57, 58/
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contains
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! Product of two GF(64) field elements
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function gf64_product(i1,i2)
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integer, intent(in) :: i1,i2
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integer :: gf64_product
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if(i1.ne.0.and.i2.ne.0) then
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gf64_product=gf64exp(mod(gf64log(i1)+gf64log(i2),63))
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else
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gf64_product=0
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endif
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end function gf64_product
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! Inverse of a GF(64) field element for arguments in [1,63]. Undefined otherwise.
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function gf64_inverse(i1)
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integer, intent(in) :: i1
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integer :: gf64_inverse
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if(i1.gt.1) then
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gf64_inverse=gf64exp(63-gf64log(i1))
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else
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gf64_inverse=1
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endif
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end function gf64_inverse
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! Sum two GF(64) field elements
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function gf64_sum(i1,i2)
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integer, intent(in) :: i1,i2
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integer :: gf64_sum
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gf64_sum=ieor(i1,i2)
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end function gf64_sum
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end module gf64math
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