| Routines

09720: THE 'SCANNING RND' ROUTINE

The address of this routine is derived from an offset found in the scanning function table.
S_RND | 09720 | CALL SYNTAX_Z | Unless syntax is being checked, jump to calculate a random number.
| 09723 | JR Z,S_RND_END
| 09725 | LD BC,(23670) | Fetch the current value of SEED.
| 09729 | CALL STACK_BC | Put it on the calculator stack.
| 09732 | RST 40 | Now use the calculator.
| 09733 | DEFB 161 | stk_one
| 09734 | DEFB 15 | addition: The 'last value' is now SEED+1.
| 09735 | DEFB 52 | stk_data: Put the number 75 on the calculator stack.
| 09736 | DEFB 55,22
| 09738 | DEFB 4 | multiply: 'last value' (SEED+1)*75.
| 09739 | DEFB 52 | stk_data: Put the number 65537 on the calculator stack.
| 09740 | DEFB 128,65,0,0,128
| 09745 | DEFB 50 | n_mod_m: Divide (SEED+1)*75 by 65537 to give a 'remainder' and an 'answer'.
| 09746 | DEFB 2 | delete: Discard the 'answer'.
| 09747 | DEFB 161 | stk_one
| 09748 | DEFB 3 | subtract: The 'last value' is now 'remainder' - 1.
| 09749 | DEFB 49 | duplicate: Make a copy of the 'last value'.
| 09750 | DEFB 56 | end_calc: The calculation is finished.
| 09751 | CALL FP_TO_BC | Use the 'last value' to give the new value for SEED.
| 09754 | LD (23670),BC
| 09758 | LD A,(HL) | Fetch the exponent of 'last value'.
| 09759 | AND A | Jump forward if the exponent is zero.
| 09760 | JR Z,S_RND_END
| 09762 | SUB 16 | Reduce the exponent, i.e. divide 'last value' by 65536 to give the required 'last value'.
| 09764 | LD (HL),A
S_RND_END | 09765 | JR S_PI_END | Jump past the S_PI routine.