Category : Files from Magazines
Archive   : PJ91.ZIP
Filename : RAND.ASM

title rand - random number
include asm.inc

public rand
public random

.data
; these primes come from Knuth's Seminumerical Algorithms
; useful prime numbers, table 1, section 4.5.4, page 390
ran_num dw 0 ; random number seed
ran_mod dw 0FFEFh ; modulus 2^16-17
ran_mul dw 0FFD9h ; multiplier 2^16-39
ran_inc dw 0FFFFh ; increment -1

.code

;; rand
;
; exit AX random number
;
rand proc
push dx
mov ax,ran_num[bp]
mul ran_mul[bp]
add ax,ran_inc[bp]
adc dx,ZER0
div ran_mod[bp]
xchg ax,dx
mov ran_num[bp],ax
pop dx
ret
rand endp


;; random
;
; entry AX num
; exit AX random number between 0 and num-1
;
random proc
pushm cx,dx
mov cx,ax
movx dx,0
jcxz ran1
call rand
div cx
ran1: mov ax,dx
popm dx,cx
ret
random endp

end