github.com/zuoyebang/bitalosdb@v1.1.1-0.20240516111551-79a8c4d8ce20/bitree/bdb/page.go

// Copyright 2021 The Bitalosdb author(hustxrb@163.com) and other contributors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package bdb

import (
	"fmt"
	"os"
	"sort"
	"unsafe"

	"github.com/cockroachdb/errors"
)

const pageHeaderSize = unsafe.Sizeof(page{})

const minKeysPerPage = 2

const branchPageElementSize = unsafe.Sizeof(branchPageElement{})
const leafPageElementSize = unsafe.Sizeof(leafPageElement{})

const (
	branchPageFlag   = 0x01
	leafPageFlag     = 0x02
	metaPageFlag     = 0x04
	freelistPageFlag = 0x10
)

const (
	bucketLeafFlag = 0x01
)

type pgid uint64

type page struct {
	id       pgid
	flags    uint16
	count    uint16
	overflow uint32
}

func (p *page) typ() string {
	if (p.flags & branchPageFlag) != 0 {
		return "branch"
	} else if (p.flags & leafPageFlag) != 0 {
		return "leaf"
	} else if (p.flags & metaPageFlag) != 0 {
		return "meta"
	} else if (p.flags & freelistPageFlag) != 0 {
		return "freelist"
	}
	return fmt.Sprintf("unknown<%02x>", p.flags)
}

func (p *page) meta() *meta {
	return (*meta)(unsafeAdd(unsafe.Pointer(p), unsafe.Sizeof(*p)))
}

func (p *page) leafPageElement(index uint16) *leafPageElement {
	return (*leafPageElement)(unsafeIndex(unsafe.Pointer(p), unsafe.Sizeof(*p),
		leafPageElementSize, int(index)))
}

func (p *page) leafPageElements() []leafPageElement {
	if p.count == 0 {
		return nil
	}
	var elems []leafPageElement
	data := unsafeAdd(unsafe.Pointer(p), unsafe.Sizeof(*p))
	unsafeSlice(unsafe.Pointer(&elems), data, int(p.count))
	return elems
}

func (p *page) branchPageElement(index uint16) *branchPageElement {
	return (*branchPageElement)(unsafeIndex(unsafe.Pointer(p), unsafe.Sizeof(*p),
		unsafe.Sizeof(branchPageElement{}), int(index)))
}

func (p *page) branchPageElements() []branchPageElement {
	if p.count == 0 {
		return nil
	}
	var elems []branchPageElement
	data := unsafeAdd(unsafe.Pointer(p), unsafe.Sizeof(*p))
	unsafeSlice(unsafe.Pointer(&elems), data, int(p.count))
	return elems
}

func (p *page) hexdump(n int) {
	buf := unsafeByteSlice(unsafe.Pointer(p), 0, 0, n)
	fmt.Fprintf(os.Stderr, "%x\n", buf)
}

type pages []*page

func (s pages) Len() int           { return len(s) }
func (s pages) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
func (s pages) Less(i, j int) bool { return s[i].id < s[j].id }

type branchPageElement struct {
	pos   uint32
	ksize uint32
	pgid  pgid
}

func (n *branchPageElement) key() []byte {
	return unsafeByteSlice(unsafe.Pointer(n), 0, int(n.pos), int(n.pos)+int(n.ksize))
}

type leafPageElement struct {
	flags uint32
	pos   uint32
	ksize uint32
	vsize uint32
}

func (n *leafPageElement) key() []byte {
	i := int(n.pos)
	j := i + int(n.ksize)
	return unsafeByteSlice(unsafe.Pointer(n), 0, i, j)
}

func (n *leafPageElement) value() []byte {
	i := int(n.pos) + int(n.ksize)
	j := i + int(n.vsize)
	return unsafeByteSlice(unsafe.Pointer(n), 0, i, j)
}

type PageInfo struct {
	ID            int
	Type          string
	Count         int
	OverflowCount int
}

type pgids []pgid

func (s pgids) Len() int           { return len(s) }
func (s pgids) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
func (s pgids) Less(i, j int) bool { return s[i] < s[j] }

func (a pgids) merge(b pgids) pgids {
	if len(a) == 0 {
		return b
	}
	if len(b) == 0 {
		return a
	}
	merged := make(pgids, len(a)+len(b))
	mergepgids(merged, a, b)
	return merged
}

func mergepgids(dst, a, b pgids) {
	if len(dst) < len(a)+len(b) {
		panic(errors.Errorf("mergepgids bad len %d < %d + %d", len(dst), len(a), len(b)))
	}

	if len(a) == 0 {
		copy(dst, b)
		return
	}
	if len(b) == 0 {
		copy(dst, a)
		return
	}

	merged := dst[:0]

	lead, follow := a, b
	if b[0] < a[0] {
		lead, follow = b, a
	}

	for len(lead) > 0 {
		n := sort.Search(len(lead), func(i int) bool { return lead[i] > follow[0] })
		merged = append(merged, lead[:n]...)
		if n >= len(lead) {
			break
		}

		lead, follow = follow, lead[n:]
	}

	_ = append(merged, follow...)
}