Re: I wonder if I'm missing something...

Well, I will only disagree with your counting. 

The original, and now current, method does READ-SEQUENCE into a vector of ‘(unsigned-byte 8). From there, the bytes are copied into an FLI Foreign Array with element type :UINT8, and from there another FLI Foreign Array copy from FLI space back to Lisp with a coerced pointer to the same FLI arena, and with element types :FLOAT and Single-Float.

So 
		I/O -> Lisp -> FLI -> Lisp

> On Nov 9, 2025, at 02:44, Yuri Davidovsky (as work at disclosure dot ie) <[email protected]> wrote:
> 
> 
>> On 8 Nov 2025, at 23:21, David McClain (as dbm at refined-audiometrics dot com) <[email protected]> wrote:
>> 
>> So now, I can read :UINT8 bytes from a Socket stream, directly into a stack allocated octet buffer, then turn around and use the FLI:REPLACE-FOREIGN-ARRAY to convert that buffer of octets into a buffer of single-float values in just one copy operation:
>> 
>> 	(let ((buf   (make-array  16
>>                                   :element-type ‘(unsigned-byte 8))))
>> 	   (declare (dynamic-extent buf))
>> 	   (READ-SEQUENCE buf socket-stream)
>> 	   (FLI:REPLACE-FOREIGN-ARRAY my-float-vec (fli:make-pointer :type :FLOAT
>>                                                                      :address (+ 8 (SYS:OBJECT-ADDRESS buf)))
>>                                       :end2 4))
> 
> I am not quite sure you are achieving what you think you are achieving here, it seems like you are making even more copying than there was at the start. As I understand it, the data from sockets gets to LW by these steps:
> 
> 1. Data is written to the kernel’s network buffer. We are not involved here in any way.
> 2. A kernel call to recv() from LW fills the underlying buffer of the socket-stream by copying from the network buffer. No way to avoid copying here (sort of, kinda possible in Linux).
> 3. You copy data from the stream into your own buffer making Lisp calls to read-byte and read-sequence.
> 
> There is only one “unneeded” copying at step 2 but it is needed if you want to work with a Lisp stream. Since read-sequence does not work in your case, so you just should use read-byte and go on about your day. If you really do not want to use read-byte here, then you just patch into the step 2 with your own buffer and avoid using the Lisp byte stream altogether.