Hello,
The mission is to copy the least significant bits from the "value"
parameter
to the "dest address" pointer at the "dest bit index" parameter which can
be
anywhere in memory up to "bit count".
So for example (conceptually):
Copy the first 3 bits from value to dest address 1000 at bit index 10000
The prototype looks like:
procedure WriteLongwordBits( Value : longword; BitCount : longword;
DestAddress : pointer; DestBitIndex : longword );
begin
end;
The assembler for the empty prototype looks like:
Project1.dpr.1204: begin
00409068 55 push ebp
00409069 8BEC mov ebp,esp
0040906B 83C4F4 add esp,-$0c
0040906E 894DF4 mov [ebp-$0c],ecx
00409071 8955F8 mov [ebp-$08],edx
00409074 8945FC mov [ebp-$04],eax
// your code can come here or so...
Project1.dpr.1208: end;
00409077 8BE5 mov esp,ebp
00409079 5D pop ebp
0040907A C20400 ret $0004
The calling code must use:
value must be in eax
bitcount must be in edx
destaddress must be in ecx
destbitindex must be pushed (4 bytes)
call routine
Many different implementations could be made.
For example:
A1. Assume the destination is all cleared with zero's
vs alternatively/better:
A2. Clear the bits yourself first. (preferred)
or
B1. Assume it's ok to overwrite trailing bits.
vs
B2. Preserve other bits which are not supposed to be modified (preferred).
No range checking needs to be done, assume the buffer is large enough.
The prototype is the 32 bit version.
I have three Delphi versions:
29 instructions 8 bit version (A2B2)
28 instructions 16 bit version (A2B2)
85 instructions 32 bit version (A2B2) <- this is where the pain begins.
(it
uses int64's which are simulated in Delphi)
So I am starting to wonder if I need to write a special 32 bit assembler
version to get some decent speed, since the speed in Delphi is lacking. <-
Pissy ;) :)
So I think that's why it's time for a contest, a pretty difficult one this
time.
Show me what you got ! ;) :)
Later I will try to implement my own asm version, but I don't want to
influence you people.
So give it a try !
If nobody supplies code than I won't either, otherwise I will post code
too
:)
Bye,
Skybuck.
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