Compiler setting for accurate math?

[bplus]

Code: (Select All)

Dim x
For x = 1 To -0.001 Step -.05
    Print Round2$(x, -2)
    _Limit 4
Next x


Function N2S$ (EXP$) 'remove scientific Notation to String (~40 LOC)
    'SMcNeill Jan 7, 2020 ref: https://www.qb64.org/forum/index.php?topic=1555.msg112989#msg112989
    'Last Function in code marked Best Answer (removed debug comments and blank lines added these 2 lines.)
    ReDim t$, sign$, l$, r$, r&&
    ReDim dp As Long, dm As Long, ep As Long, em As Long, check1 As Long, l As Long, i As Long
    t$ = LTrim$(RTrim$(EXP$))
    If Left$(t$, 1) = "-" Or Left$(t$, 1) = "N" Then sign$ = "-": t$ = Mid$(t$, 2)
    dp = InStr(t$, "D+"): dm = InStr(t$, "D-")
    ep = InStr(t$, "E+"): em = InStr(t$, "E-")
    check1 = Sgn(dp) + Sgn(dm) + Sgn(ep) + Sgn(em)
    If check1 < 1 Or check1 > 1 Then N2S = _Trim$(EXP$): Exit Function 'If no scientic notation is found, or if we find more than 1 type, it's not SN!
    Select Case l 'l now tells us where the SN starts at.
        Case Is < dp: l = dp
        Case Is < dm: l = dm
        Case Is < ep: l = ep
        Case Is < em: l = em
    End Select
    l$ = Left$(t$, l - 1) 'The left of the SN
    r$ = Mid$(t$, l + 1): r&& = Val(r$) 'The right of the SN, turned into a workable long
    If InStr(l$, ".") Then 'Location of the decimal, if any
        If r&& > 0 Then
            r&& = r&& - Len(l$) + 2
        Else
            r&& = r&& + 1
        End If
        l$ = Left$(l$, 1) + Mid$(l$, 3)
    End If
    Select Case r&&
        Case 0 'what the heck? We solved it already?
            'l$ = l$
        Case Is < 0
            For i = 1 To -r&&
                l$ = "0" + l$
            Next
            l$ = "." + l$
        Case Else
            For i = 1 To r&&
                l$ = l$ + "0"
            Next
            l$ = l$
    End Select
    N2S$ = sign$ + l$
End Function

Function Round2$ (anyNumber As _Float, dp As Long) ' uses N2S$
    ' 5 and up at decimal place dp+1 > +1 at decimal place  4 and down  > +0 at dp

    '2 1 0.-1 -2 -3 -4 ...  pick dp like this for this Round$ Function
    Dim sn$, dot, predot, postdot, rtn$

    sn$ = N2S$(Str$(anyNumber + .5 * 10 ^ dp)) 'get rid of sci notation, steve trims it so next find dot
    dot = InStr(sn$, ".")
    If dot Then
        predot = dot - 1
        postdot = Len(sn$) - (dot + 1)
    Else
        predot = Len(sn$)
        postdot = 0
    End If
    ' xxx.yyyyyy  dp = -2
    '      ^ dp
    If dp >= 0 Then
        rtn$ = Mid$(sn$, 1, predot - dp) + String$(dp, "0")
    Else
        rtn$ = Mid$(sn$, 1, predot) + "." + Mid$(sn$, dot + 1, -dp)
    End If
    If rtn$ = "" Then Round2$ = "0" Else Round2$ = rtn$
End Function

A few LOC less than string math and still QB64