From 8abfecb95cb52a54b416531755172ec103a529ea Mon Sep 17 00:00:00 2001
From: gzdaijie <gzdaijie@gmail.com>
Date: Sun, 29 Mar 2020 22:24:42 +0800
Subject: [PATCH] init geebolt

---
 gee-bolt/day1-pages/go.mod  |  3 ++
 gee-bolt/day1-pages/meta.go | 33 ++++++++++++++
 gee-bolt/day1-pages/page.go | 88 +++++++++++++++++++++++++++++++++++++
 3 files changed, 124 insertions(+)
 create mode 100644 gee-bolt/day1-pages/go.mod
 create mode 100644 gee-bolt/day1-pages/meta.go
 create mode 100644 gee-bolt/day1-pages/page.go

diff --git a/gee-bolt/day1-pages/go.mod b/gee-bolt/day1-pages/go.mod
new file mode 100644
index 0000000..17b5990
--- /dev/null
+++ b/gee-bolt/day1-pages/go.mod
@@ -0,0 +1,3 @@
+module geebolt
+
+go 1.13
diff --git a/gee-bolt/day1-pages/meta.go b/gee-bolt/day1-pages/meta.go
new file mode 100644
index 0000000..4e9cdb1
--- /dev/null
+++ b/gee-bolt/day1-pages/meta.go
@@ -0,0 +1,33 @@
+package geebolt
+
+import (
+	"errors"
+	"hash/fnv"
+	"unsafe"
+)
+
+// Represent a marker value to indicate that a file is a gee-bolt DB
+const magic uint32 = 0xED0CDAED
+
+type meta struct {
+	magic    uint32
+	pageSize uint32
+	pgid     uint64
+	checksum uint64
+}
+
+func (m *meta) sum64() uint64 {
+	var h = fnv.New64a()
+	_, _ = h.Write((*[unsafe.Offsetof(meta{}.checksum)]byte)(unsafe.Pointer(m))[:])
+	return h.Sum64()
+}
+
+func (m *meta) validate() error {
+	if m.magic != magic {
+		return errors.New("invalid magic number")
+	}
+	if m.checksum != m.sum64() {
+		return errors.New("invalid checksum")
+	}
+	return nil
+}
diff --git a/gee-bolt/day1-pages/page.go b/gee-bolt/day1-pages/page.go
new file mode 100644
index 0000000..18fc492
--- /dev/null
+++ b/gee-bolt/day1-pages/page.go
@@ -0,0 +1,88 @@
+package geebolt
+
+import (
+	"fmt"
+	"reflect"
+	"unsafe"
+)
+
+const pageHeaderSize = unsafe.Sizeof(page{})
+const branchPageElementSize = unsafe.Sizeof(branchPageElement{})
+const leafPageElementSize = unsafe.Sizeof(leafPageElement{})
+const maxKeysPerPage = 1024
+
+const (
+	branchPageFlag uint16 = iota
+	leafPageFlag
+	metaPageFlag
+	freelistPageFlag
+)
+
+type page struct {
+	id       uint64
+	flags    uint16
+	count    uint16
+	overflow uint32
+}
+
+type leafPageElement struct {
+	pos   uint32
+	ksize uint32
+	vsize uint32
+}
+
+type branchPageElement struct {
+	pos   uint32
+	ksize uint32
+	pgid  uint64
+}
+
+func (p *page) typ() string {
+	switch p.flags {
+	case branchPageFlag:
+		return "branch"
+	case leafPageFlag:
+		return "leaf"
+	case metaPageFlag:
+		return "meta"
+	case freelistPageFlag:
+		return "freelist"
+	}
+	return fmt.Sprintf("unknown<%02x>", p.flags)
+}
+
+func (p *page) meta() *meta {
+	return (*meta)(unsafe.Pointer(uintptr(unsafe.Pointer(p)) + pageHeaderSize))
+}
+
+func (p *page) dataPtr() unsafe.Pointer {
+	return unsafe.Pointer(&reflect.SliceHeader{
+		Data: uintptr(unsafe.Pointer(p)) + pageHeaderSize,
+		Len:  int(p.count),
+		Cap:  int(p.count),
+	})
+}
+
+func (p *page) leafPageElement(index uint16) *leafPageElement {
+	off := pageHeaderSize + uintptr(index)*leafPageElementSize
+	return (*leafPageElement)(unsafe.Pointer(uintptr(unsafe.Pointer(p)) + off))
+}
+
+func (p *page) leafPageElements() []leafPageElement {
+	if p.count == 0 {
+		return nil
+	}
+	return *(*[]leafPageElement)(p.dataPtr())
+}
+
+func (p *page) branchPageElement(index uint16) *branchPageElement {
+	off := pageHeaderSize + uintptr(index)*branchPageElementSize
+	return (*branchPageElement)(unsafe.Pointer(uintptr(unsafe.Pointer(p)) + off))
+}
+
+func (p *page) branchPageElements() []branchPageElement {
+	if p.count == 0 {
+		return nil
+	}
+	return *(*[]branchPageElement)(p.dataPtr())
+}