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definition.go
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definition.go
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package words
import (
"io"
"os"
"sync"
)
type defSource struct {
file *os.File // opened at startup and never closed
fileSize int64
blkSize int64
}
func loadDefinitionSource(filename string) (*defSource, error) {
// text file of WORD\tdefinition\n with LC_ALL=C sort
f, err := os.Open(filename)
if err != nil {
return nil, err
}
fileOk := false
defer func() {
if !fileOk {
f.Close()
}
}()
fileInfo, err := f.Stat()
if err != nil {
return nil, err
}
fileSize := fileInfo.Size()
blkSize := getBlkSize(&fileInfo, 4096)
fileOk = true
return &defSource{file: f, fileSize: fileSize, blkSize: blkSize}, err
}
var bufPool = sync.Pool{
New: func() interface{} {
return []byte(nil)
},
}
func (ds *defSource) bulkDefine(sortedWords []string) (map[string]string, error) {
f := ds.file
fileSize := ds.fileSize
blkSize := ds.blkSize
pooledBuf := bufPool.Get().([]byte)
if cap(pooledBuf) < int(blkSize) {
pooledBuf = make([]byte, int(blkSize))
}
defer bufPool.Put(pooledBuf)
buf := pooledBuf[:blkSize]
bufMin := int64(0)
bufMax := int64(0)
numBlks := (fileSize + blkSize - 1) / blkSize
// this "reinvents" mmap with a single block cache; it is not as performant, but it is portable
readByte := func(ofs int64) (byte, error) {
if ofs >= bufMin && ofs < bufMax {
return buf[ofs-bufMin], nil
}
if ofs < 0 || ofs >= fileSize {
return 0, io.EOF
}
innerOfs := ofs % blkSize
outerOfs := ofs - innerOfs
// unlike Seek, ReadAt does not use the file pointer, so it is ok to have multiple goroutines read the same file
n, err := f.ReadAt(buf, outerOfs)
if err != nil && err != io.EOF {
return 0, err
}
bufMin = outerOfs
bufMax = bufMin + int64(n)
if innerOfs >= int64(n) {
return 0, io.EOF
}
return buf[innerOfs], nil
}
ret := make(map[string]string)
cur := int64(0)
for _, word := range sortedWords {
var def []byte
var ofs int64
var b byte
var err error
lo := cur/blkSize + 1 // exclude current block
origLo := lo
// binary search among remaining blocks
for hi := numBlks; lo < hi; {
mid := int64(uint64(lo+hi) >> 1)
ofs = mid * blkSize
// skip to newline (because this is after the current block)
for ; ; ofs++ {
b, err = readByte(ofs)
if err == io.EOF {
goto high
} else if err != nil {
return nil, err
} else if b == '\n' {
ofs++
// compare the word starting at ofs vs word
for _, c := range []byte(word) {
b, err = readByte(ofs)
if err == io.EOF {
goto high
} else if err != nil {
return nil, err
} else if b > c {
goto high
} else if b < c || b == '\t' {
goto low
}
ofs++
}
b, err = readByte(ofs)
if err == io.EOF {
goto after_match
} else if err != nil {
return nil, err
} else if b == '\t' {
goto found
}
goto high
}
}
low:
// block's first word is not greater (it may be found here)
lo = mid + 1
continue
high:
// block's first word is greater, exclude
hi = mid
}
// compare current block vs binary search result
if lo == origLo {
ofs = cur
goto start_of_possibly_matching_line
}
// skip to newline (because this is after the current block)
ofs = (lo - 1) * blkSize
before_match:
for ; ; ofs++ {
b, err = readByte(ofs)
if err == io.EOF {
break
} else if err != nil {
return nil, err
} else if b == '\n' {
ofs++
break
}
}
start_of_possibly_matching_line:
// now ofs is at start of line, linear search from there
cur = ofs
for _, c := range []byte(word) {
b, err = readByte(ofs)
if err == io.EOF {
goto after_match
} else if err != nil {
return nil, err
} else if b > c {
goto after_match
} else if b < c || b == '\t' {
goto before_match
}
ofs++
}
b, err = readByte(ofs)
if err == io.EOF {
goto after_match
} else if err != nil {
return nil, err
} else if b == '\t' {
goto found
}
goto after_match
found:
// ofs points at the '\t'
def = make([]byte, 0)
for ofs++; ; ofs++ {
b, err = readByte(ofs)
if err == io.EOF {
break
} else if err != nil {
return nil, err
} else if b == '\n' {
ofs++
break
} else {
def = append(def, b)
}
}
ret[word] = string(def)
cur = ofs
after_match:
}
return ret, nil
}