psi: created crc.go to put crc stuff in and renamed op.go to helpers.go

stream/mts/psi/op.go

@@ -1,145 +0,0 @@
-/*
-NAME
-	op.go
-DESCRIPTION
-  op.go provides functionality for editing and reading bytes slices
-	directly in order to insert/read timestamp and location data in psi.
-
-AUTHOR
-  Saxon Milton <saxon@ausocean.org>
-
-LICENSE
-  op.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 http://www.gnu.org/licenses.
-*/
-
-package psi
-
-import (
-	"bytes"
-	"encoding/binary"
-	"errors"
-	"hash/crc32"
-	"math/bits"
-)
-
-// TimeBytes takes a timestamp as an uint64 and converts to an 8 byte slice -
-// allows for updating of timestamp in pmt time descriptor.
-func TimeBytes(t uint64) []byte {
-	var s [timeDataSize]byte
-	binary.BigEndian.PutUint64(s[:], t)
-	return s[:]
-}
-
-// HasTime takes a psi as a byte slice and checks to see if it has a time descriptor
-// - if so return nil, otherwise return error
-func HasTime(p []byte) error {
-	if p[timeTagIndx] != timeDescTag {
-		return errors.New("PSI does not contain a time descriptor, cannot update")
-	}
-	return nil
-}
-
-// HasLocation takes a psi as a byte slice and checks to see if it has a location descriptor
-// - if so return nil, otherwise return error
-func HasLocation(p []byte) error {
-	if p[locationTagIndx] != locationDescTag {
-		return errors.New("PSI does not contain a location descriptor, cannot update")
-	}
-	return nil
-}
-
-// UpdateTime takes the byte slice representation of a psi-pmt as well as a time
-// as an integer and attempts to update the time descriptor in the pmt with the
-// given time if the time descriptor exists, otherwise an error is returned
-func UpdateTime(dst []byte, t uint64) error {
-	err := HasTime(dst)
-	if err != nil {
-		return err
-	}
-	ts := TimeBytes(uint64(t))
-	for i := range dst[timeDataIndx : timeDataIndx+timeDataSize] {
-		dst[i+timeDataIndx] = ts[i]
-	}
-	dst = updateCrc(dst)
-	return nil
-}
-
-// TimeFrom takes a byte slice representation of a psi-pmt and extracts it's
-// timestamp, returning as a uint64 if it exists, otherwise returning 0 and nil
-// if it does not exist
-func TimeFrom(p []byte) (t uint64, err error) {
-	err = HasTime(p)
-	if err != nil {
-		return 0, err
-	}
-	t = binary.BigEndian.Uint64(p[timeDataIndx : timeDataIndx+timeDataSize])
-	return t, nil
-}
-
-// LocationFrom takes a byte slice representation of a psi-pmt and extracts it's
-// timestamp, returning as a uint64 if it exists, otherwise returning 0 and nil
-// if it does not exist
-func LocationFrom(p []byte) (g string, err error) {
-	err = HasLocation(p)
-	if err != nil {
-		return "", err
-	}
-	gBytes := p[locationDataIndx : locationDataIndx+locationDataSize]
-	gBytes = bytes.Trim(gBytes, "\x00")
-	g = string(gBytes)
-	return g, nil
-}
-
-// LocationStrBytes take a string of location data and converts to a 32 byte slice -
-// easy update of slice representation of a pmt with location descriptor
-func LocationStrBytes(s string) []byte {
-	var b [locationDataSize]byte
-	copy(b[:], s)
-	return b[:]
-}
-
-// UpdateLocation takes a byte slice representation of a psi-pmt containing a location
-// descriptor and attempts to update the location data value with the passed string.
-// If the psi does not contain a location descriptor, and error is returned.
-func UpdateLocation(d []byte, s string) error {
-	err := HasLocation(d)
-	if err != nil {
-		return err
-	}
-	gb := LocationStrBytes(s)
-	for i := range d[locationDataIndx : locationDataIndx+locationDataSize] {
-		d[i+locationDataIndx] = gb[i]
-	}
-	d = updateCrc(d)
-	return nil
-}
-
-// addCrc appends a crc table to a given psi table in bytes
-func addCrc(out []byte) []byte {
-	out = append(out, make([]byte, 4)...)
-	out = updateCrc(out)
-	return out
-}
-
-// updateCrc updates the crc of psi bytes slice that may have been modified
-func updateCrc(out []byte) []byte {
-	crc32 := crc32_Update(0xffffffff, crc32_MakeTable(bits.Reverse32(crc32.IEEE)), out[1:len(out)-4])
-	out[len(out)-4] = byte(crc32 >> 24)
-	out[len(out)-3] = byte(crc32 >> 16)
-	out[len(out)-2] = byte(crc32 >> 8)
-	out[len(out)-1] = byte(crc32)
-	return out
-}

stream/mts/psi/psi.go

@@ -26,10 +26,6 @@ LICENSE
 
 package psi
 
-import (
-	"hash/crc32"
-)
-
 // Lengths of section definitions
 const (
 	ESSDDefLen = 5
@@ -308,26 +304,3 @@ func byteToBool(b byte) (o bool) {
 	}
 	return
 }
-
-func crc32_MakeTable(poly uint32) *crc32.Table {
-	var t crc32.Table
-	for i := range t {
-		crc := uint32(i) << 24
-		for j := 0; j < 8; j++ {
-			if crc&0x80000000 != 0 {
-				crc = (crc << 1) ^ poly
-			} else {
-				crc <<= 1
-			}
-		}
-		t[i] = crc
-	}
-	return &t
-}
-
-func crc32_Update(crc uint32, tab *crc32.Table, p []byte) uint32 {
-	for _, v := range p {
-		crc = tab[byte(crc>>24)^v] ^ (crc << 8)
-	}
-	return crc
-}