Function RTSAFE(X1, X2, XACC)
    MAXIT = 100
    Call FUNCD(X1, FL, DF)
    Call FUNCD(X2, FH, DF)
    If FL * FH >= 0 Then Print "root must be bracketed"
    If FL < 0 Then
        XL = X1
        XH = X2
    Else
        XH = X1
        XL = X2
        SWAP = FL
        FL = FH
        FH = SWAP
    End If
    RTSAFE = 0.5 * (X1 + X2)
    DXOLD = Abs(X2 - X1)
    DX = DXOLD
    Call FUNCD(RTSAFE, F, DF)
    For J = 1 To MAXIT
        DUM = (RTSAFE - XH) * DF - F * ((RTSAFE - XL) * DF - F)
        If DUM >= 0 Or Abs(2 * F) > Abs(DXOLD * DF) Then
            DXOLD = DX
            DX = 0.5 * (XH - XL)
            RTSAFE = XL + DX
            If XL = RTSAFE Then Exit Function
        Else
            DXOLD = DX
            DX = F / DF
            TEMP = RTSAFE
            RTSAFE = RTSAFE - DX
            If TEMP = RTSAFE Then Exit Function
        End If
        If Abs(DX) < XACC Then Exit Function
        Call FUNCD(RTSAFE, F, DF)
        If F < 0 Then
            XL = RTSAFE
            FL = F
        Else
            XH = RTSAFE
            FH = F
        End If
    Next J
    Print "RTSAFE exceeding maximum iterations."
End Function