[fpc-devel] The

[J. Gareth Moreton]

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" fpc-develfpc-devel at lists.freepascal.org sent:
> 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;
> 
>       
> 
>  
>  
> 
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