Random Numbers

[britlion]

We haven't looked at this in a while.

Here's some test code:

Code:

FUNCTION FASTCALL randomBase () as uByte ASM random: ld hl,$A280 ; xz -> yw ld de,$C0DE ; yw -> zt ld (random+1),de ; x = y, z = w ld a,e ; w = w ^ ( w << 3 ) add a,a add a,a add a,a xor e ld e,a ld a,h ; t = x ^ (x << 1) add a,a xor h ld d,a rra ; t = t ^ (t >> 1) ^ w xor d xor e ld h,l ; y = z ld l,a ; w = t ld (random+4),hl ret END ASM END FUNCTION FUNCTION FASTCALL randomFixed() as FIXED ASM call random push AF call random ld l,A POP AF ld h,a ld d,0 ld e,d END ASM END FUNCTION FUNCTION t() as uLong asm DI LD DE,(23674) LD D,0 LD HL,(23672) EI end asm end function DIM time,endtime as uLong REM Print the base random 8 bits: print randomBase() REM print as a decimal, like basic's random number: print randomFixed() REM Works the same way: print int(randomFixed()*10) pause 1 pause 0 cls dim n as uInteger REM how does this look as a random dot spread? time=t() for n=1 to 30000 plot rnd*255,rnd*192 'print at 0,0;INT(rnd) next n REM (it looks good) endtime=t() print endtime-time;" Frames" pause 1 pause 0 cls REM how does this look as a random dot spread? time=t() for n=1 to 30000 plot randomFixed()*255,randomFixed()*192 'print at 0,0;INT( randomFixed() ) next n REM (it looks good) endtime=t() print endtime-time;" Frames"

Basically, more than twice as fast in all cases.

I think the clincher, for me, is that even

Code:

print at 0,0;INT(CAST(FLOAT,randomFixed()))

- which forces a full floating point result, like rnd has, comes back 50% faster.

I also tried it with my planet proggy - <!-- l --><a class="postlink-local" href="https://forum.boriel.com/bug-reports/byte-loops-solved-t757.html#p3229">bug-reports/byte-loops-solved-t757.html#p3229</a><!-- l --> - it comes out over twice as fast.