四手和 Kahan 和

PROGRAM test
   IMPLICIT NONE
   INTEGER :: i
   REAL :: x, s, c, t
   c = 0.0
   s = 0.0
   DO i = 1, 100
    x = 0.01 - c
    t = s + x
    c = (t - s) - x
    s = t
    PRINT *, s, c
   END DO
   PRINT *, s == 1.0, s  
   STOP
END PROGRAM test