43 lines
1.4 KiB
Text
43 lines
1.4 KiB
Text
# select_nth.ludic - :nth-child's formulas
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# :nth-child(odd), (even), (3), (2n+1), (n+2), (-n+3): is the k-th child one of them. The a and b of
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# an + b are read once per argument (matched per element per frame, a read made text every time)
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const MM_NTH: int = -16 # n1 a, n2 b
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function sel_nth(ui_st: mut UiState, arg: string, k: int) -> bool {
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if arg == "odd" { return k % 2 == 1 }
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if arg == "even" { return k % 2 == 0 }
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let m = mm_of(ui_st)
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let i = mm_find(m, MM_NTH, arg)
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if i >= 0 {
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ui_st.nth_a = int(m.n1[i])
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ui_st.nth_b = int(m.n2[i])
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} else { sel_nth_read(ui_st, m, arg) }
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let a = ui_st.nth_a
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let b = ui_st.nth_b
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if a == 0 { return k == b }
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let d = k - b
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return d % a == 0 and d / a >= 0
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}
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@alloc_ok("a memo miss: once per :nth-child argument, bounded by MM_CAP")
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function sel_nth_read(ui_st: mut UiState, m: UiMemo, arg: string) -> void {
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var npos = -1
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for i in 0 .. len(arg) {
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if arg[i] == 110 { npos = i }
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}
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var a = 0
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var b = 0
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if npos < 0 { b = int(el_num(arg)) } else {
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a = 1
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let head: string = arg[0..npos]
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if head == "-" { a = -1 } else if len(head) > 0 { a = int(el_num(head)) }
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var tail = tpl_words(arg[npos + 1..len(arg)])
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if len(tail) > 0 and tail[0] == 43 { tail = tpl_words(tail[1..len(tail)]) }
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if len(tail) > 0 { b = int(el_num(tail)) }
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}
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ui_st.nth_a = a
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ui_st.nth_b = b
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let j = mm_add(m, MM_NTH, arg)
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if j >= 0 {
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m.n1[j] = float(a)
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m.n2[j] = float(b)
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}
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}
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