millfork/include/i80/random_i80.mfk

import random

#if not(ARCH_I80)
#warn stdlib_i80 module should be only used on Intel 8080-like targets
#endif

#pragma zilog_syntax

asm byte rand() {
    ld b,8
    ld hl,(rand_seed)
__rand_loop:
    add hl,hl
    ? jp nc, __no_eor
    ld a,l
    xor $2D
    ld l,a
__no_eor:
#if CPUFEATURE_Z80
    djnz __rand_loop
#else
    dec b
    ? jp nz, __rand_loop
#endif
    ld (rand_seed),hl
    ? ret
}

#if CPUFEATURE_Z80

inline asm void init_rand_seed() {
    ld a,r
    ld (rand_seed), a
    ld a,r
    ld (rand_seed+1), a
    ? ret
}

#else

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

#endif