// Add appends the bits given its size to the vector.
func (v *BitVector) Add(bits uint64, size int) {
if size <= 0 || size > 64 {
panic("ranksel: bit size must be in range [1,64]")
}
// Add bits
v.bits.Add(bits, size)
vlength := v.bits.Len()
// Increment popcount
popcnt := bit.PopCount(bits)
v.popcount += popcnt
// Update rank sampling
lenranks := len(v.ranks)
overflow := vlength - (lenranks * v.opts.Sr)
if overflow > 0 {
v.ranks = append(v.ranks, 0)
rank := bit.Rank(bits, size-overflow-1)
v.ranks[lenranks] = v.popcount - popcnt + rank
}
// Update select sampling
lenidx := len(v.indices)
overflow = v.popcount - (lenidx * v.opts.Ss)
if overflow > 0 {
v.indices = append(v.indices, 0)
sel := bit.Select(bits, popcnt-overflow+1)
v.indices[lenidx] = (vlength - size + sel) & ^0x3F
}
}
// select11 returns the index of the ith 11 pair.
func select11_64(v uint64, i int) int {
// Same with popcount11
v &= v >> 1
v &= ^(v >> 1)
// Perform regular select
return bit.Select(v, i)
}
// Get returns the value at index i.
func (a *Array) Get(i int) int {
start := a.selector.Select1(i + 1)
bits := a.selector.Get(start, min(64, a.selector.Len()-start))
length := bit.Select(bits, 2)
code := a.bits.Get(start, length)
return decode(code, length)
}
// Select0 returns the index of the ith zero. Panics
// if i is zero or greater than the number of zeroes.
// This is slower than Select1 in most cases.
func (v *BitVector) Select0(i int) int {
if i > (v.bits.Len() - v.popcount) {
panic("ranksel: input exceeds number of 0s")
} else if i == 0 {
panic("ranksel: input must be greater than 0")
}
// Do a binary search on the rank samples to find
// the largest rank sample that is less than i.
// From https://en.wikipedia.org/wiki/Binary_search_algorithm
imin := 1
imax := len(v.ranks) - 1
for imin < imax {
imid := imin + ((imax - imin) >> 1)
rmid0 := (imid * v.opts.Sr) - v.ranks[imid]
if rmid0 < i {
imin = imid + 1
} else {
imax = imid
}
}
imin--
idx := 0
vbits := v.bits.Bits()
aidx := (imin * v.opts.Sr) >> 6
rank0 := (imin * v.opts.Sr) - v.ranks[imin]
for ii, b := range vbits[aidx:] {
b = ^b
rank0 += bit.PopCount(b)
if rank0 >= i {
overflow := rank0 - i
popcnt := bit.PopCount(b)
idx = (aidx + ii) << 6
idx += bit.Select(b, popcnt-overflow)
break
}
}
return idx
}
// Select1 returns the index of the ith set bit.
// Panics if i is zero or greater than the number
// of set bits.
func (v *BitVector) Select1(i int) int {
if i > v.popcount {
panic("ranksel: input exceeds number of 1s")
} else if i == 0 {
panic("ranksel: input must be greater than 0")
}
j := (i - 1) / v.opts.Ss
q := v.indices[j] / v.opts.Sr
k := 0
r := 0
rq := v.ranks[q:]
for k, r = range rq {
if r >= i {
k--
break
}
}
idx := 0
rank := rq[k]
vbits := v.bits.Bits()
aidx := ((q + k) * v.opts.Sr) >> 6
for ii, b := range vbits[aidx:] {
rank += bit.PopCount(b)
if rank >= i {
overflow := rank - i
popcnt := bit.PopCount(b)
idx = (aidx + ii) << 6
idx += bit.Select(b, popcnt-overflow)
break
}
}
return idx
}
