[Coco] Pascal random() for OS-9 and DEFT

[Robert Gault]

Willard Goosey wrote:
> I've finally finished one of my little projects!

Here is a routine I've used in an OS-9 C program which could easily be 
converted to straight asm use.

#include <time.h>
direct char rand[5];       /* used by random number routine */
struct registers {
     char rg_cc,rg_a,rg_b,rg_dp;
     unsigned rg_x,rg_y,rg_u;
     };

struct registers reg;

main()
  {
   int rnd(),*reg_d;
   reg_d=&reg.rg_a; /* reg.rg_a & reg.rg_b now addressed by reg_d */

     /* get random seed for rnd from system time */
     getime(&buffer); /* see time.h */
     temp=&buffer;
     for(i=0;i<5;i++)
        rand[i]=*(temp+i+1);

     /* example of rnd use
     x/=(rnd(8)+2);   */

/* Stack checking can be removed here for speed increase */
int rnd(val) /* standard rnd rountine replaced with faster asm; no floats */
unsigned val;
{
#asm
  ldb 5,s
  incb
  andcc #$fe
  lda <rand+4
  bita #1
  beq r1
  lda #8
  eora <rand
  sta <rand
  lda #128
  eora <rand
  sta <rand
  orcc #1
r1 ror <rand
  ror <rand+1
  ror <rand+2
  ror <rand+3
  ror <rand+4
  pshs b
  lda <rand+1
  mul
  ldb ,s
  sta ,s
  lda <rand
  mul
  addb ,s+
  adca #0
  clrb
  stb 4,s
  sta 5,s
#endasm
  return val; /* whole number returned; no fractional part */
  }