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//
// Copyright (c) SAS Institute Inc.
//
// 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 comdoc
import (
"bytes"
"encoding/binary"
)
// Read the master/meta sector allocation table. It is an array of all the
// sectors holding pieces of the sector allocation table (SAT). The main file
// header holds 109 MSAT entries and MSATNextSector may point to a sector
// holding yet more. The last entry in each additional sector points to another
// sector holding more MSAT entries, or -2 if none.
func (r *ComDoc) readMSAT() error {
r.MSAT = r.Header.MSAT[:]
r.msatList = nil
nextSector := r.Header.MSATNextSector
count := r.SectorSize / 4
values := make([]SecID, count)
for nextSector >= 0 {
if err := r.readSectorStruct(nextSector, values); err != nil {
return err
}
r.MSAT = append(r.MSAT, values[:count-1]...)
r.msatList = append(r.msatList, nextSector)
nextSector = values[count-1]
}
// trim free slots
for i := len(r.MSAT) - 1; i >= 0; i-- {
if r.MSAT[i] >= 0 {
r.MSAT = r.MSAT[:i+1]
break
}
}
return nil
}
// Allocate sectors for the SAT and MSAT
func (r *ComDoc) allocSectorTables() {
// work out how many sectors are needed for both
satPerSector := r.SectorSize / 4
msatPerSector := satPerSector - 1
for {
if len(r.SAT)%satPerSector != 0 {
panic("irregularly sized sector table")
}
satSectors := len(r.SAT) / satPerSector
if satSectors > len(r.MSAT) {
// allocate a new SAT sector
sector := r.makeFreeSectors(1, false)[0]
r.MSAT = append(r.MSAT, sector)
r.SAT[sector] = SecIDSAT
// a new SAT might be needed so check again
continue
}
// 109 MSAT entries fit into the file header, the rest need more sectors
msatSectors := (len(r.MSAT) - msatInHeader + msatPerSector - 1) / msatPerSector
if msatSectors > len(r.msatList) {
// allocate a new MSAT sector
sector := r.makeFreeSectors(1, false)[0]
r.msatList = append(r.msatList, sector)
r.SAT[sector] = SecIDMSAT
// a new SAT might be needed so check again
continue
}
break
}
}
// Write an updated MSAT out to the header and msatSectors, with satSectors
// being the contents of the MSAT
func (r *ComDoc) writeMSAT() error {
satPerSector := r.SectorSize / 4
msatPerSector := satPerSector - 1
// round MSAT up to the next full sector and mark all unused spaces as free
msatCount := msatInHeader + len(r.msatList)*msatPerSector
msat := make([]SecID, msatCount)
copy(msat, r.MSAT)
for i := len(r.MSAT); i < msatCount; i++ {
msat[i] = SecIDFree
}
// copy the first 109 into the file header
copy(r.Header.MSAT[:], msat)
msat = msat[msatInHeader:]
// write remaining sectors
buf := bytes.NewBuffer(r.sectorBuf)
chunk := make([]SecID, r.SectorSize/4)
for i, sector := range r.msatList {
j := i * msatPerSector
copy(chunk, msat[j:j+msatPerSector])
// set pointer to next MSAT sector
if i < len(r.msatList)-1 {
chunk[msatPerSector] = r.msatList[i+1]
} else {
chunk[msatPerSector] = SecIDEndOfChain
}
// write
buf.Reset()
_ = binary.Write(buf, binary.LittleEndian, chunk)
if err := r.writeSector(sector, buf.Bytes()); err != nil {
return err
}
}
if len(r.msatList) > 0 {
r.Header.MSATNextSector = r.msatList[0]
} else {
r.Header.MSATNextSector = SecIDEndOfChain
}
return nil
}
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