134 lines
3.7 KiB
Go
134 lines
3.7 KiB
Go
// +build 386 amd64,!appengine
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package roaring
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import (
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"errors"
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"io"
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"reflect"
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"runtime"
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"unsafe"
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)
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func (ac *arrayContainer) writeTo(stream io.Writer) (int, error) {
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buf := uint16SliceAsByteSlice(ac.content)
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return stream.Write(buf)
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}
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func (bc *bitmapContainer) writeTo(stream io.Writer) (int, error) {
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if bc.cardinality <= arrayDefaultMaxSize {
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return 0, errors.New("refusing to write bitmap container with cardinality of array container")
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}
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buf := uint64SliceAsByteSlice(bc.bitmap)
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return stream.Write(buf)
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}
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func uint64SliceAsByteSlice(slice []uint64) []byte {
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// make a new slice header
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header := *(*reflect.SliceHeader)(unsafe.Pointer(&slice))
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// update its capacity and length
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header.Len *= 8
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header.Cap *= 8
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// instantiate result and use KeepAlive so data isn't unmapped.
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result := *(*[]byte)(unsafe.Pointer(&header))
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runtime.KeepAlive(&slice)
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// return it
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return result
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}
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func uint16SliceAsByteSlice(slice []uint16) []byte {
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// make a new slice header
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header := *(*reflect.SliceHeader)(unsafe.Pointer(&slice))
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// update its capacity and length
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header.Len *= 2
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header.Cap *= 2
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// instantiate result and use KeepAlive so data isn't unmapped.
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result := *(*[]byte)(unsafe.Pointer(&header))
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runtime.KeepAlive(&slice)
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// return it
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return result
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}
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func (bc *bitmapContainer) asLittleEndianByteSlice() []byte {
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return uint64SliceAsByteSlice(bc.bitmap)
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}
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// Deserialization code follows
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////
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// These methods (byteSliceAsUint16Slice,...) do not make copies,
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// they are pointer-based (unsafe). The caller is responsible to
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// ensure that the input slice does not get garbage collected, deleted
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// or modified while you hold the returned slince.
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////
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func byteSliceAsUint16Slice(slice []byte) (result []uint16) { // here we create a new slice holder
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if len(slice)%2 != 0 {
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panic("Slice size should be divisible by 2")
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}
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// reference: https://go101.org/article/unsafe.html
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// make a new slice header
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bHeader := (*reflect.SliceHeader)(unsafe.Pointer(&slice))
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rHeader := (*reflect.SliceHeader)(unsafe.Pointer(&result))
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// transfer the data from the given slice to a new variable (our result)
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rHeader.Data = bHeader.Data
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rHeader.Len = bHeader.Len / 2
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rHeader.Cap = bHeader.Cap / 2
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// instantiate result and use KeepAlive so data isn't unmapped.
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runtime.KeepAlive(&slice) // it is still crucial, GC can free it)
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// return result
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return
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}
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func byteSliceAsUint64Slice(slice []byte) (result []uint64) {
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if len(slice)%8 != 0 {
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panic("Slice size should be divisible by 8")
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}
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// reference: https://go101.org/article/unsafe.html
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// make a new slice header
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bHeader := (*reflect.SliceHeader)(unsafe.Pointer(&slice))
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rHeader := (*reflect.SliceHeader)(unsafe.Pointer(&result))
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// transfer the data from the given slice to a new variable (our result)
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rHeader.Data = bHeader.Data
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rHeader.Len = bHeader.Len / 8
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rHeader.Cap = bHeader.Cap / 8
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// instantiate result and use KeepAlive so data isn't unmapped.
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runtime.KeepAlive(&slice) // it is still crucial, GC can free it)
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// return result
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return
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}
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func byteSliceAsInterval16Slice(slice []byte) (result []interval16) {
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if len(slice)%4 != 0 {
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panic("Slice size should be divisible by 4")
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}
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// reference: https://go101.org/article/unsafe.html
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// make a new slice header
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bHeader := (*reflect.SliceHeader)(unsafe.Pointer(&slice))
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rHeader := (*reflect.SliceHeader)(unsafe.Pointer(&result))
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// transfer the data from the given slice to a new variable (our result)
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rHeader.Data = bHeader.Data
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rHeader.Len = bHeader.Len / 4
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rHeader.Cap = bHeader.Cap / 4
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// instantiate result and use KeepAlive so data isn't unmapped.
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runtime.KeepAlive(&slice) // it is still crucial, GC can free it)
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// return result
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return
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}
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