[ clisp-Patches-688545 ] preliminary fast POSITION

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Patches item #688545, was opened at 2003-02-18 10:24
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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Jörg Höhle (hoehle)
Assigned to: Nobody/Anonymous (nobody)
Summary: preliminary fast POSITION

Initial Comment:
The sequence functions carry an immense amount of 
overhead. As a result, POSITION, COUNT etc. are much 
slower than one would expect.

I advocate that CLISP should recognize optimizable 
cases and handle them internally. The time to test 
internally at run-time for optimizable cases is 
negligible compared to the full-blown sequence and 
stepping overhead.

Specifically, I advocate that CLISP handles optimizable 
cases transparently and does not expose something like 
EXT:VECTOR-POSITION. CLISP should encourage portable 
code and thus use of POSITION etc., with guarantees 
that it will be fast where it can be.

Optimizable cases are, at a glance
o vector instead sequence (possibly only string or 
unsigned-byte 8/16/32)
o and test EQ or EQL (or maybe CHAR= and = with 
corresponding array element-type)
o with KEY #'IDENTITY
o :from-end is optimizable as well (means almost 
duplicate code).

So far, I only implemented string-position, ignoring 
test and from-end. Maybe somebody will want to 
continue work from this.

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