84 lines
1.7 KiB
Text
84 lines
1.7 KiB
Text
low-level
|
||
Лекция 8
|
||
|
||
Короткий Фёдор
|
||
|
||
* Low Level Programming
|
||
|
||
* package unsafe
|
||
|
||
import "unsafe"
|
||
|
||
fmt.Println(unsafe.Sizeof(float64(0))) // "8"
|
||
|
||
- `unsafe` выглядит как обычный пакет
|
||
- Но реализован в компиляторе
|
||
|
||
* package unsafe
|
||
|
||
type Pointer *ArbitraryType
|
||
|
||
- Два преобразования
|
||
|
||
*T -> unsafe.Pointer
|
||
unsafe.Pointer -> *T
|
||
|
||
- `unsafe.Pointer` - это _настоящий_ `void*`
|
||
|
||
func Float64bits(f float64) uint64 {
|
||
return *(*uint64)(unsafe.Pointer(&f))
|
||
}
|
||
|
||
* unsafe.Pointer
|
||
|
||
.code unsafeptr/main.go /var/,/42/
|
||
|
||
Действия с указателями дожны выполняться *атомарно*.
|
||
|
||
.code unsafeptr/main.go /\+wrong/,/\-wrong/
|
||
|
||
Иначе сборщик мусора освободит память используемого объекта.
|
||
|
||
pT := uintptr(unsafe.Pointer(new(T))) // NOTE: wrong!
|
||
|
||
* unsafe tricks
|
||
|
||
// A Builder is used to efficiently build a string using Write methods.
|
||
// It minimizes memory copying. The zero value is ready to use.
|
||
// Do not copy a non-zero Builder.
|
||
type Builder struct {
|
||
buf []byte
|
||
}
|
||
|
||
// String returns the accumulated string.
|
||
func (b *Builder) String() string {
|
||
return *(*string)(unsafe.Pointer(&b.buf))
|
||
}
|
||
|
||
// *-----*-----*-----*
|
||
// * ptr * len * cap * // []byte
|
||
// *-----*-----*-----*
|
||
//
|
||
// *-----*-----*
|
||
// * ptr * len * // string
|
||
// *-----*-----*
|
||
|
||
* cgo
|
||
|
||
.code bzip/bzip2.c /include/,/^}/
|
||
|
||
* cgo
|
||
|
||
.code bzip/bzip2.go /package/,/import/
|
||
|
||
.code bzip/bzip2.go /type writer/,/^}/
|
||
|
||
* cgo
|
||
|
||
.code bzip/bzip2.go /type writer/,/^}/
|
||
|
||
.code bzip/bzip2.go /func NewWriter/,/^}/
|
||
|
||
* cgo
|
||
|
||
.code bzip/bzip2.go /func .* Write/,/^}/
|