compression

Documentation

Overview

Package compression provides common types for other compression packages.

Index

• type Level
  • func (l Level) Interpolate(fastest int32, fast int32, default_ int32, small int32, smallest int32) int32
• type Reader
• type Writer

Types

type Level

type Level int32

Level configures the compression trade-off between speed and size.

A lower (more negative) value means better speed (faster). A higher (more positive) value means better size (smaller).

const (
	// LevelFastest means to maximize compression speed.
	LevelFastest Level = -2 << 10

	// LevelFast means to prioritize compression speed.
	//
	// It might not be as fast as LevelFastest, if doing so would require
	// substantial additional compute resources (e.g. CPU or RAM) or give up
	// substantial compression size.
	LevelFast Level = -1 << 10

	// LevelDefault means to use a reasonable default.
	LevelDefault Level = 0

	// LevelSmall means to prioritize compression size.
	//
	// It might not be as small as LevelSmallest, if doing so would require
	// substantial additional compute resources (e.g. CPU or RAM) or give up
	// substantial compression speed.
	LevelSmall Level = +1 << 10

	// LevelSmallest means to minimize compression size.
	LevelSmallest Level = +2 << 10
)

func (Level) Interpolate

func (l Level) Interpolate(fastest int32, fast int32, default_ int32, small int32, smallest int32) int32

Interpolate translates from Level (a codec-agnostic concept) to a codec-specific compression level numbering scheme. For exampe, a zlib package might translate LevelFastest to 1 and LevelSmallest to 9 by calling Interpolate(1, 2, 6, 9, 9).

The mapping is via piecewise linear interpolation, given by five points in (Level, int32) space: (LevelFastest, fastest), (LevelFast, fast), etc.

type Reader

type Reader interface {
	io.ReadCloser

	// Reset resets this Reader to switch to a new underlying io.Reader. This
	// permits re-using a Reader instead of allocating a new one.
	//
	// It is the same as the standard library's zlib.Resetter's method.
	Reset(r io.Reader, dictionary []byte) error
}

Reader is an io.ReadCloser with a Reset method.

type Writer

type Writer interface {
	io.WriteCloser

	// Reset resets this Writer to switch to a new underlying io.Writer. This
	// permits re-using a Writer instead of allocating a new one.
	Reset(w io.Writer, dictionary []byte, level Level) error
}

Writer is an io.WriteCloser with a Reset method.