av/codec/h264/h264dec/helpers.go

/*
DESCRIPTION
  helpers.go provides general helper utilities.

AUTHORS
  Saxon Nelson-Milton <saxon@ausocean.org>, The Australian Ocean Laboratory (AusOcean)

LICENSE
  rtp.go is Copyright (C) 2018 the Australian Ocean Lab (AusOcean)

  It is free software: you can redistribute it and/or modify them
  under the terms of the GNU General Public License as published by the
  Free Software Foundation, either version 3 of the License, or (at your
  option) any later version.

  It is distributed in the hope that it will be useful, but WITHOUT
  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
 for more details.

  You should have received a copy of the GNU General Public License
  along with revid in gpl.txt.  If not, see [GNU licenses](http://www.gnu.org/licenses).
*/

package h264dec

import (
	"errors"
	"math"
)

// binToSlice is a helper function to convert a string of binary into a
// corresponding byte slice, e.g. "0100 0001 1000 1100" => {0x41,0x8c}.
// Spaces in the string are ignored.
func binToSlice(s string) ([]byte, error) {
	var (
		a     byte = 0x80
		cur   byte
		bytes []byte
	)

	for i, c := range s {
		switch c {
		case ' ':
			continue
		case '1':
			cur |= a
		case '0':
		default:
			return nil, errors.New("invalid binary string")
		}

		a >>= 1
		if a == 0 || i == (len(s)-1) {
			bytes = append(bytes, cur)
			cur = 0
			a = 0x80
		}
	}
	return bytes, nil
}

// binToInt converts a binary string provided as a string and returns as an int.
// White spaces are ignored.
func binToInt(s string) (int, error) {
	var sum int
	var nSpace int
	for i := len(s) - 1; i >= 0; i-- {
		if s[i] == ' ' {
			nSpace++
			continue
		}
		sum += int(math.Pow(2, float64(len(s)-1-i-nSpace))) * int(s[i]-'0')
	}
	return sum, nil
}

func maxi(a, b int) int {
	if a > b {
		return a
	}
	return b
}

func mini(a, b int) int {
	if a < b {
		return a
	}
	return b
}

func absi(a int) int {
	if a < 0 {
		return -a
	}
	return a
}