bit_packers.go

package bitpacking

const (
	Min4b, Max4b = 0, (1 << 4) - 1
	Min6b, Max6b = 0, (1 << 6) - 1
	Min7b, Max7b = 0, (1 << 7) - 1
)

func Pack2x4b(vs [2]byte) byte { return (vs[1] << 4) | (0x0F & vs[0]) }

func Unpack2x4b(vs byte) [2]byte { return [2]byte{0x0F & vs, vs >> 4} }

func Pack4x6b(vs [4]byte) [3]byte {
	return [3]byte{
		(vs[1] | ((vs[0] << 2) & 0xC0)),
		(vs[2] | ((vs[0] << 4) & 0xC0)),
		(vs[3] | ((vs[0] << 6) & 0xC0)),
	}
}

func Unpack4x6b(vs [3]byte) [4]byte {
	var v0 byte
	for i := range 3 {
		v0 |= (vs[i] & 0xC0) >> ((i + 1) * 2)
	}
	return [4]byte{
		v0,
		(vs[0] & 0x3F),
		(vs[1] & 0x3F),
		(vs[2] & 0x3F),
	}
}

func Pack8x7b(vs [8]byte) [7]byte {
	return [7]byte{
		(vs[1] | ((vs[0] << 1) & 0x80)),
		(vs[2] | ((vs[0] << 2) & 0x80)),
		(vs[3] | ((vs[0] << 3) & 0x80)),
		(vs[4] | ((vs[0] << 4) & 0x80)),
		(vs[5] | ((vs[0] << 5) & 0x80)),
		(vs[6] | ((vs[0] << 6) & 0x80)),
		(vs[7] | ((vs[0] << 7) & 0x80)),
	}
}

func Unpack8x7b(vs [7]byte) [8]byte {
	var v0 byte
	for i := range 7 {
		v0 |= (vs[i] & 0x80) >> (i + 1)
	}
	return [8]byte{
		v0,
		(vs[0] & 0x7F),
		(vs[1] & 0x7F),
		(vs[2] & 0x7F),
		(vs[3] & 0x7F),
		(vs[4] & 0x7F),
		(vs[5] & 0x7F),
		(vs[6] & 0x7F),
	}
}