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// Copyright 2013 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package liveness
import "cmd/compile/internal/bitvec"
// FNV-1 hash function constants.
const (
h0 = 2166136261
hp = 16777619
)
// bvecSet is a set of bvecs, in initial insertion order.
type bvecSet struct {
index []int // hash -> uniq index. -1 indicates empty slot.
uniq []bitvec.BitVec // unique bvecs, in insertion order
}
func (m *bvecSet) grow() {
// Allocate new index.
n := len(m.index) * 2
if n == 0 {
n = 32
}
newIndex := make([]int, n)
for i := range newIndex {
newIndex[i] = -1
}
// Rehash into newIndex.
for i, bv := range m.uniq {
h := hashbitmap(h0, bv) % uint32(len(newIndex))
for {
j := newIndex[h]
if j < 0 {
newIndex[h] = i
break
}
h++
if h == uint32(len(newIndex)) {
h = 0
}
}
}
m.index = newIndex
}
// add adds bv to the set and returns its index in m.extractUnique,
// and whether it is newly added.
// If it is newly added, the caller must not modify bv after this.
func (m *bvecSet) add(bv bitvec.BitVec) (int, bool) {
if len(m.uniq)*4 >= len(m.index) {
m.grow()
}
index := m.index
h := hashbitmap(h0, bv) % uint32(len(index))
for {
j := index[h]
if j < 0 {
// New bvec.
index[h] = len(m.uniq)
m.uniq = append(m.uniq, bv)
return len(m.uniq) - 1, true
}
jlive := m.uniq[j]
if bv.Eq(jlive) {
// Existing bvec.
return j, false
}
h++
if h == uint32(len(index)) {
h = 0
}
}
}
// extractUnique returns this slice of unique bit vectors in m, as
// indexed by the result of bvecSet.add.
func (m *bvecSet) extractUnique() []bitvec.BitVec {
return m.uniq
}
func hashbitmap(h uint32, bv bitvec.BitVec) uint32 {
n := int((bv.N + 31) / 32)
for i := 0; i < n; i++ {
w := bv.B[i]
h = (h * hp) ^ (w & 0xff)
h = (h * hp) ^ ((w >> 8) & 0xff)
h = (h * hp) ^ ((w >> 16) & 0xff)
h = (h * hp) ^ ((w >> 24) & 0xff)
}
return h
}
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