# [erlang-questions] Bit syntax

Bob Cowdery <>
Wed Mar 9 16:29:43 CET 2011

```Yes. I realised that as soon as I sent the message. I guess bad match
accounts for a large number of error messages. All seems to be working now.

Bob

On 09/03/2011 15:17, Bob Ippolito wrote:
> 8*51 is 408 (which is by coincidence the same as the number of bits),
> 16#00 is 0. Either way you're extending it to 408 bits.
>
> You're getting a bad match presumably because A, B, and/or C are
> already bound in your shell. Do an f(). first to forget all of the
> bound variables in the shell, and then it will work.
>
> 1> <<A:24, B:48, C:408>> = <<16#effe02:24,16#00:48,16#00:408>>.
> <<239,254,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
>   0,0,0,...>>
> 2> {A, B, C}.
> {15728130,0,0}
>
> On Wed, Mar 9, 2011 at 7:09 AM, Bob Cowdery <> wrote:
>> What I actually want is 51 bytes of 16#00.
>>
>> 12> <<A:24, B:48, C:408>> = <<16#effe02:24,16#00:48,16#00:408>>.
>> ** exception error: no match of right hand side value
>>
>> <<239,254,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
>>                      0,0,0,...>>
>>
>> Why is this different. Isn't it just saying 00 as a 408 bit number
>> rather than (8*51)?
>>
>> Bob
>>
>> On 09/03/2011 14:55, Vlad Dumitrescu wrote:
>>> Your C is 8*51 as a 408 bit number. You probably want 16#00:408 instead.
>>>
>>>
>>> On Wed, Mar 9, 2011 at 15:50, Bob Cowdery <
>>> <mailto:>> wrote:
>>>
>>>     Thanks. The syntax did look a bit odd for a repeating group. I
>>>     pulled it
>>>     off the web somewhere.
>>>
>>>     So if I say:
>>>
>>>     7> <<A:24, B:48, C:408>> = <<16#effe02:24,16#00:48,(8*51):408>>
>>>     .
>>>     <<239,254,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
>>>      0,0,0,...>>
>>>     8> A.
>>>     15728130
>>>     9> B.
>>>     0
>>>     10> C.
>>>     408
>>>
>>>     What do these bound values mean. C is supposed to be 51 zero bytes
>>>     (408
>>>     bits). Why is C bound to the number of bits.
>>>
>>>     Bob
>>>
>>>     On 09/03/2011 14:29, Vlad Dumitrescu wrote:
>>>     > Hi!
>>>     >
>>>     > On Wed, Mar 9, 2011 at 15:21, Bob Cowdery
>>>     < <mailto:>
>>>     > <mailto:
>>>     <mailto:>>> wrote:
>>>     >
>>>     >     Hi
>>>     >
>>>     >     I'm clearly not understanding the bit syntax properly. Could
>>>     someone
>>>     >     explain to me what I am doing wrong here. Why does the first
>>>     not match
>>>     >     when its the right shape but the second does when its the
>>>     wrong shape.
>>>     >     The bound values don't make much sense to me either.
>>>     >
>>>     >     1> <<A:24, B:48, C:408>> =
>>>     <<16#effe02:24,16#00:48,16#00,(8*51):408>>.
>>>     >     ** exception error: no match of right hand side value
>>>     >
>>>     >
>>>     > There is an "extra" 16#00 on the right side that is not matched
>>>     on the
>>>     > left.
>>>     >
>>>     >
>>>     >     2> <<A:32, B:48, C:408>> =
>>>     <<16#effe02:24,16#00:48,16#00,(8*51):408>>.
>>>     >
>>>     >
>>>     > The larger size for A "swallows" the extra value, but shifts the
>>>     > values a byte to the right.
>>>     >
>>>     > regards,
>>>     >
>>>
>>>
>>
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```