diff options
Diffstat (limited to 'src/prng.s')
| -rw-r--r-- | src/prng.s | 35 |
1 files changed, 35 insertions, 0 deletions
@@ -9,6 +9,14 @@ ;; Current random value. Initialized on the title to game transition. zp_rand = $0A + ;; Last random value as stored by + ;; Prng::random_non_repeated_valid_y_coordinate(). + zp_last_rand = $12 + + ;; How many attempts should Prng::random_non_repeated_valid_y_coordinate() + ;; take to find a unique value. + RAND_ATTEMPTS = 3 + ;; Updates the 'a' register with the next random number set after the ;; current value of `zp_rand`, while also making sure that it is a valid ;; screen Y coordinate. @@ -21,6 +29,33 @@ sta zp_rand rts .endproc + + ;; Calls Prng::random_valid_y_coordinate() multiple times until we get a + ;; different value than what we got the last time we called this + ;; function. Realistically this should just take 1 attempt for most cases, + ;; and in the worst case just 2. Nevertheless, we have set a generous value + ;; to 'RAND_ATTEMPTS' just in case. + ;; + ;; NOTE: the 'y' register is preserved. + .proc random_non_repeated_valid_y_coordinate + tya + pha + ldy #RAND_ATTEMPTS + + @again: + jsr Prng::random_valid_y_coordinate + cmp Prng::zp_last_rand + bne @end + dey + bne @again + + @end: + sta Prng::zp_last_rand + pla + tay + lda Prng::zp_last_rand + rts + .endproc .endscope |