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"
(C) 2011 by Holger Hans Peter Freyther
All Rights Reserved
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as
published by the Free Software Foundation, either version 3 of the
License, or (at your option) any later version.
This program 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 Affero General Public License for more details.
You should have received a copy of the GNU Affero General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
"
ByteArray extend [
decodeGSM7Bit [
<category: '*-osmo-gsm'>
^ GSMDecoding decode: self.
]
]
String extend [
asGSM7Bit [
"I convert a string into a 7bit encoded string. I should
also be in UnicodeString but I am not. This impl. is just
basic and does not deal with difficult bits."
<category: '*-osmo-gsm'>
^ GSMEncoding encode: self.
]
asUSSD7Bit [
"I convert a string into a 7bit encoded string. I know about
padding rules for USSD messages."
<category: '*-osmo-gsm'>
^ GSMUSSDEncoding encode: self.
]
]
Object subclass: GSMDecoding [
<category: 'osmo-gsm'>
<comment: 'I am the base class for GSM Decoding as of GSM 03.38. I
can be subclassed to deal with specifics for USSD and other systems.'>
GSMDecoding class >> decode: aByteArray [
| bits bytes |
bits := self convertFromBytes: aByteArray.
bytes := self convertToBytes: bits.
^ self handleBytes: bytes from: bits
]
GSMDecoding class >> handleBytes: bytes from: bits [
^ bytes asString
]
GSMDecoding class >> convertFromBytes: aByteArray [
| bits |
"We convert the stream into single bits. It is the
easiest to do it like this."
bits := OrderedCollection new.
aByteArray do: [:each |
1 to: 8 do: [:pos | bits add: (each bitAt: pos)]
].
^ bits
]
GSMDecoding class >> convertToBytes: bits [
| bytes |
bytes := ByteArray new: (bits size // 7).
1 to: bits size by: 7 do: [:pos |
(pos + 6 <= bits size) ifTrue: [ | byte |
byte := 0.
byte := (byte bitShift: 1) bitOr: (bits at: pos + 6).
byte := (byte bitShift: 1) bitOr: (bits at: pos + 5).
byte := (byte bitShift: 1) bitOr: (bits at: pos + 4).
byte := (byte bitShift: 1) bitOr: (bits at: pos + 3).
byte := (byte bitShift: 1) bitOr: (bits at: pos + 2).
byte := (byte bitShift: 1) bitOr: (bits at: pos + 1).
byte := (byte bitShift: 1) bitOr: (bits at: pos + 0).
bytes at: (pos // 7) + 1 put: byte.
].
].
^ bytes
]
]
Object subclass: GSMEncoding [
<category: 'osmo-gsm'>
<comment: 'I am the base class for GSM Encoding as of GSM 03.38. I
can be subclassed to deal with specifics for USSD and other systems.'>
GSMEncoding class >> encode: aString [
| bits |
bits := self convertToBits: aString.
self padBits: bits on: aString.
^ self convertToBytes: bits.
]
GSMEncoding class >> padBits: bits on: aString [
"I have to make sure that bits can be divided by/8"
| rest |
rest := 8 - (bits size \\ 8).
rest to: 1 by: -1 do: [:each | bits add: 0].
]
GSMEncoding class >> convertToBits: aString [
| bits |
bits := OrderedCollection new: (aString size * 7) // 8.
"Split it into bits"
aString do: [:char | | val |
val := char value.
1 to: 7 do: [:digit | bits add: (val bitAt: digit)].
].
^ bits
]
GSMEncoding class >> convertToBytes: bits [
| bytes |
bytes := ByteArray new: bits size // 8.
1 to: bits size by: 8 do: [:each | | byte |
byte := 0.
byte := (byte bitShift: 1) bitOr: (bits at: each + 7).
byte := (byte bitShift: 1) bitOr: (bits at: each + 6).
byte := (byte bitShift: 1) bitOr: (bits at: each + 5).
byte := (byte bitShift: 1) bitOr: (bits at: each + 4).
byte := (byte bitShift: 1) bitOr: (bits at: each + 3).
byte := (byte bitShift: 1) bitOr: (bits at: each + 2).
byte := (byte bitShift: 1) bitOr: (bits at: each + 1).
byte := (byte bitShift: 1) bitOr: (bits at: each + 0).
bytes at: (each // 8) + 1 put: byte.
].
^ bytes
]
]
GSMEncoding subclass: GSMUSSDEncoding [
<category: 'osmo-gsm'>
<comment: 'I know the funky stuff for USSD encoding/padding'>
GSMUSSDEncoding class >> padBits: bits on: aString [
| rest nl |
"Check if we are on a byte boundary and a CR."
((aString last = Character cr) and: [(bits size \\ 8) = 0]) ifTrue: [ | cr |
cr := Character cr value.
1 to: 7 do: [:each | bits add: (cr bitAt: each) ].
bits add: 0.
^ self
].
"Check if we need to handle this, if not continue."
aString size \\ 8 = 7
ifFalse: [^ super padBits: bits on: aString].
"Now add the padding."
rest := 8 - (bits size \\ 8).
rest = 7 ifFalse: [^self error: 'The rest should be 7 bits but were %1' % rest].
nl := Character cr value.
1 to: 7 do: [:each | bits add: (nl bitAt: each)].
]
]
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