h264/bits: new BitReader to eventually replace BitReader in read.go

[saxon-milton]

This is working towards resolving issue #30.

[kortschak]

Looking at the complexity of this, I think you'd be better taking the code in bzip2 and adding a PeekBits. That is a trivial addition, using essentially the same code that is in ReadBits, but first Peeking the bytes to need to read the given number of bits. That would be (untested):

func (br *bitReader) PeekBits64(bits uint) (n uint64) {
	byt, err := br.r.Peek(int(n+7) / 8)
	if err != nil {
		if err == io.EOF {
			err = io.ErrUnexpectedEOF
		}
		br.err = err
		return 0
	}
	for i := 0; bits > br.bits; i++ {
		b := byt[i]
		if err != nil {
			br.err = err
			return 0
		}
		br.n <<= 8
		br.n |= uint64(b)
		br.bits += 8
	}

	n = (br.n >> (br.bits - bits)) & ((1 << bits) - 1)
	br.bits -= bits
	return
}

This requires that the copied version of bit_reader.go has the io.ByteReader field changed to either a *bufio.Reader or a local interface type interface { io.Reader; Peek(n int) ([]byte, error) } and do the appropriate check during construction of the bit reader.

[saxon-milton]

Looking at the complexity of this, I think you'd be better taking the code in bzip2 and adding a PeekBits. That is a trivial addition, using essentially the same code that is in ReadBits, but first Peeking the bytes to need to read the given number of bits. That would be (untested):

func (br *bitReader) PeekBits64(bits uint) (n uint64) {
	byt, err := br.r.Peek(int(n+7) / 8)
	if err != nil {
		if err == io.EOF {
			err = io.ErrUnexpectedEOF
		}
		br.err = err
		return 0
	}
	for i := 0; bits > br.bits; i++ {
		b := byt[i]
		if err != nil {
			br.err = err
			return 0
		}
		br.n <<= 8
		br.n |= uint64(b)
		br.bits += 8
	}

	n = (br.n >> (br.bits - bits)) & ((1 << bits) - 1)
	br.bits -= bits
	return
}

This requires that the copied version of bit_reader.go has the io.ByteReader field changed to either a *bufio.Reader or a local interface type interface { io.Reader; Peek(n int) ([]byte, error) } and do the appropriate check during construction of the bit reader.

Do I need to do any acknowledgement of the original code if I use this ?

[kortschak]

The bit_reader.go code is in the standard library. The standard approaches to using third party code apply.

[saxon-milton]

The bit_reader.go code is in the standard library. The standard approaches to using third party code apply.

so I need to put this in the file header:
Copyright (c) 2009 The Go Authors. All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:

• Redistributions of source code must retain the above copyright
  notice, this list of conditions and the following disclaimer.
• Redistributions in binary form must reproduce the above
  copyright notice, this list of conditions and the following disclaimer
  in the documentation and/or other materials provided with the
  distribution.
• Neither the name of Google Inc. nor the names of its
  contributors may be used to endorse or promote products derived from
  this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

??

[kortschak]

This license only applies to portions (admittedly major portions). You should also include whatever license we are applying to this.

Say which file it was derived from.

[saxon-milton]

Say which file the code was derived from ?

[kortschak]

Yes

[saxon-milton]

Can you really use two licenses on the same file ? What if conditions in the licenses clash ?

[kortschak]

If the licenses clash, you can't use them together. That's not limited to file scope. Everything that uses the standard library (i.e. all Go code since runtime is in the standard library) uses the Go license. This just makes it explicit that this code is from there.

[saxon-milton]

How does the copyright work ? Do I add the ausocean copyright too ?

[kortschak]

I would have abandoned this and started a new PR, but it is what it is. Please squash when you merge.

[kortschak]

Please squash when you merge.