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package cellbuf
// DefaultTabInterval is the default tab interval.
const DefaultTabInterval = 8
// TabStops represents horizontal line tab stops.
type TabStops struct {
stops []int
interval int
width int
}
// NewTabStops creates a new set of tab stops from a number of columns and an
// interval.
func NewTabStops(width, interval int) *TabStops {
ts := new(TabStops)
ts.interval = interval
ts.width = width
ts.stops = make([]int, (width+(interval-1))/interval)
ts.init(0, width)
return ts
}
// DefaultTabStops creates a new set of tab stops with the default interval.
func DefaultTabStops(cols int) *TabStops {
return NewTabStops(cols, DefaultTabInterval)
}
// Resize resizes the tab stops to the given width.
func (ts *TabStops) Resize(width int) {
if width == ts.width {
return
}
if width < ts.width {
size := (width + (ts.interval - 1)) / ts.interval
ts.stops = ts.stops[:size]
} else {
size := (width - ts.width + (ts.interval - 1)) / ts.interval
ts.stops = append(ts.stops, make([]int, size)...)
}
ts.init(ts.width, width)
ts.width = width
}
// IsStop returns true if the given column is a tab stop.
func (ts TabStops) IsStop(col int) bool {
mask := ts.mask(col)
i := col >> 3
if i < 0 || i >= len(ts.stops) {
return false
}
return ts.stops[i]&mask != 0
}
// Next returns the next tab stop after the given column.
func (ts TabStops) Next(col int) int {
return ts.Find(col, 1)
}
// Prev returns the previous tab stop before the given column.
func (ts TabStops) Prev(col int) int {
return ts.Find(col, -1)
}
// Find returns the prev/next tab stop before/after the given column and delta.
// If delta is positive, it returns the next tab stop after the given column.
// If delta is negative, it returns the previous tab stop before the given column.
// If delta is zero, it returns the given column.
func (ts TabStops) Find(col, delta int) int {
if delta == 0 {
return col
}
var prev bool
count := delta
if count < 0 {
count = -count
prev = true
}
for count > 0 {
if !prev {
if col >= ts.width-1 {
return col
}
col++
} else {
if col < 1 {
return col
}
col--
}
if ts.IsStop(col) {
count--
}
}
return col
}
// Set adds a tab stop at the given column.
func (ts *TabStops) Set(col int) {
mask := ts.mask(col)
ts.stops[col>>3] |= mask
}
// Reset removes the tab stop at the given column.
func (ts *TabStops) Reset(col int) {
mask := ts.mask(col)
ts.stops[col>>3] &= ^mask
}
// Clear removes all tab stops.
func (ts *TabStops) Clear() {
ts.stops = make([]int, len(ts.stops))
}
// mask returns the mask for the given column.
func (ts *TabStops) mask(col int) int {
return 1 << (col & (ts.interval - 1))
}
// init initializes the tab stops starting from col until width.
func (ts *TabStops) init(col, width int) {
for x := col; x < width; x++ {
if x%ts.interval == 0 {
ts.Set(x)
} else {
ts.Reset(x)
}
}
}
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