flat assembler
Message board for the users of flat assembler.
Index
> Macroinstructions > Generating primes (list inside a repeat block) 
Author 

l_inc 20 Oct 2015, 22:06
RIxRIpt
There are multiple things you could do: 1) Do all the calculations in the preprocessing stage by means of the rept directive. It works with numbers as well as with symbolic constants as long as they expand into numbers. High memory overhead, slow. Numbers are limited to the signed 32 bit integer range. 2) Generate a list of identifiers during preprocessing and then assign prime values to them during assembly. Moderate memory overhead, relatively fast. 3) Do all the stuff during the assembly stage only. Generate an array (dd or dq) stored into a labeled virtual addressing space (see the last two paragraphs at the end of the section "Addressing spaces"). Minimal memory overhead, fast. More flexible. _________________ Faith is a superposition of knowledge and fallacy 

20 Oct 2015, 22:06 

RIxRIpt 24 Oct 2015, 10:45
l_inc, tyvm! I didn't know about labelled virtual addressing space. Here's the final, working result:
Code: include 'exmacro/print.inc' fasm_sqrt_result = 0 macro fasm_sqrt n { local x, y x = n y = 0 while x >= 0 x = x  y y = y + 1 x = x  y end while fasm_sqrt_result = y  1 } macro generate_primes n { local x, y, i, j, slimit, sbase, number_of_primes, virtual_primes, va_offset number_of_primes = 0 virtual at 0 db 1111'1100b db 1 + (n  1) / 8 dup 1111'1111b virtual_primes:: repeat n + 1 i = %  1 load x byte from i / 8 if x and (1 shl (i and 7)) dq i number_of_primes = number_of_primes + 1 sbase = i * i slimit = 1 + (n  sbase) / i if slimit > 0 repeat slimit j = sbase + i * (%  1) load y byte from j / 8 y = y and (not (1 shl (j and 7))) store byte y at j / 8 end repeat end if end if end repeat end virtual va_offset = (n  1) / 8 + 1 + 1 repeat number_of_primes load q qword from virtual_primes:va_offset + (%  1) * 8 dq q display d=q, 13, 10 end repeat } fasm_sqrt 1 shl 31 generate_primes fasm_sqrt_result By the way, is it a bug or feature? I have to add an offset to LVAS, despite the fact the label was defined after some data. Code: virtual at 0 db 1111'1100b db 1 + (n  1) / 8 dup 1111'1111b virtual_primes:: Code: va_offset = (n  1) / 8 + 1 + 1 repeat number_of_primes load q qword from virtual_primes:va_offset + (%  1) * 8 Update: second version, with less `loads` in the main loop: Code: macro generate_primes n { local x, y, i, j, p, slimit, sbase, virtual_prime_bits virtual at 0 virtual_prime_bits:: ; 0, 1  not primes ; 2, ..  probrably primes db 1111'1100b db 1 + (n  1) / 8 dup 1111'1111b repeat (n + 1) / 8 + 1 i = %  1 load x byte from i repeat 8 j = %  1 p = i * 8 + j if p > n break end if if x and (1 shl j) sbase = p * p slimit = 1 + (n  sbase) / p if slimit > 0 repeat slimit j = sbase + p * (%  1) load y byte from j / 8 y = y and (not (1 shl (j and 7))) store byte y at j / 8 end repeat end if end if end repeat end repeat end virtual repeat (n + 1) / 8 + 1 i = %  1 load x byte from virtual_prime_bits:i repeat 8 j = %  1 if x and (1 shl j) p = i * 8 + j if p > n break end if dq p display d=p, 13, 10 end if end repeat end repeat } 

24 Oct 2015, 10:45 

l_inc 24 Oct 2015, 11:30
RIxRIpt
Quote: By the way, is it a bug or feature? I have to add an offset to LVAS, despite the fact the label was defined after some data. It's a feature. The addressing space labels refer to the addressing space only, they don't hold any information about the offset inside it. You can therefore define such label at any location of the addressing space, but keep in mind that unlike the normal labels they unfortunately cannot be forward referenced even if the data you access is not forward referenced. I.e. the following won't work: Code: outsideOffset dd 1 b_outsideAS:: virtual load val dword from f_outsideAS:outsideOffset end virtual f_outsideAS:: But it will work if you use b_outsideAS instead. As for the va_offset you can define it as a normal label to know where to start reading like virtual_primes:: va_offset: . _________________ Faith is a superposition of knowledge and fallacy 

24 Oct 2015, 11:30 

Tomasz Grysztar 24 Oct 2015, 11:40
RIxRIpt wrote: By the way, is it a bug or feature? I have to add an offset to LVAS, despite the fact the label was defined after some data. By the way, I like to use various code samples that do not use any x86 instructions, like this one, to test the compatibility of fasm g with fasm 1. So I took your macro and tested it in fasm g (obviously I had to change "{}" to "end macro")  it worked perfectly. Well, of course much slower than in fasm 1, but that's the price of the unified design that fasm g has. 

24 Oct 2015, 11:40 

RIxRIpt 24 Oct 2015, 11:49
Thanks for the explanations. I liked the analogy of :: with $$, makes sense
Quote:
Cool, I'm glad this macro is useful for at least this purpose 

24 Oct 2015, 11:49 

l_inc 24 Oct 2015, 11:50
Tomasz Grysztar
Quote: and it is this address that is the used as base when you refer to that block through "::" label. The wording is misleading. When referring to data through an addressing space label no base address is added to the expression after the colon. _________________ Faith is a superposition of knowledge and fallacy 

24 Oct 2015, 11:50 

Tomasz Grysztar 24 Oct 2015, 11:59
l_inc wrote: Tomasz Grysztar What I did mean there is that you cannot load/store at addresses smaller than that base address, because they would translate to negative offsets. 

24 Oct 2015, 11:59 

< Last Thread  Next Thread > 
Forum Rules:

Copyright © 19992023, Tomasz Grysztar. Also on GitHub, YouTube, Twitter.
Website powered by rwasa.