millfork/include/random_6502.mfk

import random

#if not(ARCH_6502)
#warn random_6502 module should be only used on 6502-compatible targets
#endif

asm byte rand() {
    ? ldx #8
    ? lda rand_seed+0
__rand_loop:
    asl
    ? rol rand_seed+1
    bcc __no_eor
    eor #$2D
__no_eor:
    dex
    bne __rand_loop
    ? sta rand_seed+0
    ? rts
}


#if CBM_64_COMPAT

void init_rand_seed() {
    poke($D40E, $ff)
    poke($D40F, $ff)
    poke($D412, $80)
    while vic_raster != $70 {}
    rand_seed.hi = peek($D41B)
    while vic_raster != $40 {}
    rand_seed.lo = peek($D41B)
}

#else

inline void init_rand_seed() {
    // TODO: find a better source of randomness
    rand_seed = 1
}

#endif