Some divisors, like 7, do not have a reciprocal that can be contained within 32 bits. Expanding to 64 bits, however, is a clever approach that I overlooked, since you can permit some loss of precision (the reason why the bit shift is required) due to the limited range. This might be worth exploring.
Gareth aka. Kit
On Tue 24/08/21 20:14 , "Marģers . via" sent:
Show quoted text 42 lines
I came up with even shorter variant of div
example
function teDWordDivBy7_v4( divided : dword):dword; assembler;
nostackframe;
asm
mov ecx,divided
mov rax,2635249153693862181
mul rcx
mov eax,edx
end;
current version for comparison
function teDWordDivBy7_v0( divided : dword):dword; assembler;
nostackframe;
asm
mov ecx,divided
mov eax,613566757
mul ecx
add edx,ecx
rcr edx,1
shr edx,2
mov eax,edx
end;
_______________________________________________
fpc-devel maillist -
https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel [1]
Links:
------
[1]
http://secureweb.fast.net.uk/parse.php?redirect=https://lists.freepascal.or
g/cgi-bin/mailman/listinfo/fpc-devel