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Tweaks.

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Nuno Cruces
2024-06-19 14:43:44 +01:00
parent 2d168136f1
commit 5c1c0f03a5
1 changed files with 22 additions and 18 deletions
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40
ext/bloom/bloom.go
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@@ -30,7 +30,7 @@ type bloom struct {
schema string
storage string
prob float64
nfilter int64
bytes int64
hashes int
}
@@ -41,15 +41,17 @@ func create(db *sqlite3.Conn, _, schema, table string, arg ...string) (_ *bloom,
storage: table + "_storage",
}
nelem := 100
var nelem int64
if len(arg) > 0 {
nelem, err = strconv.Atoi(arg[0])
nelem, err = strconv.ParseInt(arg[0], 10, 64)
if err != nil {
return nil, err
}
if nelem <= 0 {
return nil, errors.New("bloom: number of elements in filter must be positive")
}
} else {
nelem = 100
}
if len(arg) > 1 {
@@ -73,10 +75,10 @@ func create(db *sqlite3.Conn, _, schema, table string, arg ...string) (_ *bloom,
return nil, errors.New("bloom: number of hash functions must be positive")
}
} else {
t.hashes = int(math.Round(-math.Log2(t.prob)))
t.hashes = max(1, numHashes(t.prob))
}
t.nfilter = computeLength(nelem, t.prob)
t.bytes = numBytes(nelem, t.prob)
err = db.Exec(fmt.Sprintf(
`CREATE TABLE %s.%s (data BLOB, p REAL, n INTEGER, m INTEGER, k INTEGER)`,
@@ -89,7 +91,7 @@ func create(db *sqlite3.Conn, _, schema, table string, arg ...string) (_ *bloom,
`INSERT INTO %s.%s (rowid, data, p, n, m, k)
VALUES (1, zeroblob(%d), %f, %d, %d, %d)`,
sqlite3.QuoteIdentifier(t.schema), sqlite3.QuoteIdentifier(t.storage),
t.nfilter, t.prob, nelem, t.nfilter*8, t.hashes))
t.bytes, t.prob, nelem, 8*t.bytes, t.hashes))
if err != nil {
return nil, err
}
@@ -131,7 +133,7 @@ func connect(db *sqlite3.Conn, _, schema, table string, arg ...string) (_ *bloom
return nil, err
}
t.nfilter = load.ColumnInt64(0)
t.bytes = load.ColumnInt64(0)
t.prob = load.ColumnFloat(1)
t.hashes = load.ColumnInt(2)
return &t, nil
@@ -188,7 +190,7 @@ func (b *bloom) Update(arg ...sqlite3.Value) (rowid int64, err error) {
for n := 0; n < b.hashes; n++ {
hash := calcHash(n, blob)
hash %= uint64(b.nfilter * 8)
hash %= uint64(b.bytes * 8)
bitpos := byte(hash % 8)
bytepos := int64(hash / 8)
@@ -202,7 +204,7 @@ func (b *bloom) Update(arg ...sqlite3.Value) (rowid int64, err error) {
return 0, err
}
buf[0] |= (1 << bitpos)
buf[0] |= 1 << bitpos
_, err = f.Seek(bytepos, io.SeekStart)
if err != nil {
@@ -241,9 +243,9 @@ func (c *cursor) Filter(idxNum int, idxStr string, arg ...sqlite3.Value) error {
}
defer f.Close()
for n := 0; n < c.hashes; n++ {
for n := 0; n < c.hashes && !c.eof; n++ {
hash := calcHash(n, blob)
hash %= uint64(c.nfilter * 8)
hash %= uint64(c.bytes * 8)
bitpos := byte(hash % 8)
bytepos := int64(hash / 8)
@@ -257,10 +259,7 @@ func (c *cursor) Filter(idxNum int, idxStr string, arg ...sqlite3.Value) error {
return err
}
c.eof = (buf[0] & (1 << bitpos)) == 0
if c.eof {
break
}
c.eof = buf[0]&(1<<bitpos) == 0
}
return nil
}
@@ -294,7 +293,12 @@ func calcHash(k int, b []byte) uint64 {
return siphash.Hash(^uint64(k), uint64(k), b)
}
func computeLength(n int, p float64) int64 {
bits := math.Ceil(-((float64(n) * math.Log(p)) / (math.Ln2 * math.Ln2)))
return (int64(bits) + 7) / 8
func numHashes(p float64) int {
k := math.Round(-math.Log2(p))
return max(1, int(k))
}
func numBytes(n int64, p float64) int64 {
m := math.Ceil(float64(n) * math.Log(p) / -(math.Ln2 * math.Ln2))
return (int64(m) + 7) / 8
}