Subject: [rohc] sigcomp issue zliu-4 (MEMSET instruction)

From: [email-masked]
Date: Fri, 19 Apr 2002 10:44:06 -0500

Hi,

(This is probably a non-issue as most of the authors agree
on this one. But I'd like to register it here so the wider
audience is aware of it and have a chance to comment.)

During offline discussion, I've suggested to add a instruction 
MEMSET(%address, %len, %value). It is convenient for a algorithm 
that wants to set part of the UDVM buffer to a value other than 
zero. Of course, one can always do it with a loop using LOAD and
COMPARE. But that means a little larger code size and slower
execution if no compiler to compile the loop.

The feedback I got from Hans and Richard was positive (see below).
Richard further enhanced the MEMSET. I agree with him. So, does
anyone has objection? If not, I guess we can go ahead and update
the draft (before we forget about it). 

BR,
Zhigang

=================================================================
[Hans' opinion:]

> I guess the same could be achieved with a simple loop, but as 
> you say it could be more convenient to have it as an instruction. 
> 
> The UDVM currently understands 33 instructions so in my 
> opinion the cost of this addition is small.

[Richard's opinion:]

> An instruction of this type might be useful for setting up static
> dictionaries and so on. The instruction would be especially useful
> if we could vary the octets being written to the memory in some
> known manner, for example using an offset operand as follows:
> 
> MEMSET (%address, %length, %start_value, %offset)
> 
> The first octet would be set to start_value, the second octet to
> (start_value + offset) the next to (start_value + 2 * offset) etc.
> All calculations taken modulo 256, of course.

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