[cmucl-imp] string-to-octets

[Helmut Eller]

* Raymond Toy [2011-10-30 03:28] writes:

> On 10/29/11 4:18 AM, Helmut Eller wrote:
>> I'm wondering how STRING-TO-OCTETS can be used with a fixed sized byte
>> buffer.  For example we want to write a long string to a byte stream
>> using a fixed size byte buffer.  STRING-TO-OCTETS seems to return the
>> buffer and the number of bytes written.  E.g.
>>
>> (let ((buffer (make-array 20 :element-type '(unsigned-byte 8)))
>>       (string (make-string 100  :initial-element #\a)))
>>   (stream:string-to-octets string :external-format :utf32 :buffer buffer))
>>
>>
> Is this better:
>
> (let ((buffer (make-array 19 :element-type '(unsigned-byte 8)))
>            (string (make-string 100  :initial-element #\u+3b2)))
>        (multiple-value-bind (b p i last)
>            (stream:string-to-octets string :external-format :utf8
> :buffer buffer)
>          (values b p i last)))
>
> #(206 178 206 178 206 178 206 178 206 178 206 178 206 178 206 178 206
> 178 206)
> 19
> 9
> 18
>
> 9 is the number of characters converted, 18 is the index+1 in the buffer
> where the last valid octet was placed.  The last octet is the first
> octect of the 2-octet utf8 encoding for #\u+3b2.

Is 19 the number of octets written?  Or is it an index?
Might be nice to either use counts or indexes consistently.

I'm not sure that I understand the purpose of the 18.  Is this something
that is needed later?

> If no buffer is specified, the entire string is converted and the buffer
> is returned along with the number of octets generated.  (Kind of
> redundant now.)

Returning the buffer is also redundant in the case where buffer is
specified.  We can return only 3 values in registers; would it be
worthwhile to make the two cases unsymmetric?  In one case return 2 (or
3) indexes and in the other case just the buffer.

Helmut