Routines
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AD25: Generate Random Number
Returns a number from 00 up to, but not including, the limit passed in A. The Z80 Memory Refresh Register supplies the walk count: the routine counts down inside that limit once per refresh tick, wrapping to the original limit when it hits zero, then decreases the result by one more before returning. Nothing in the game calls it.
Input
A Exclusive upper bound
Output
A The generated number
Preserve BC, keep the limit, and read the refresh register for the walk count.
GenerateRandomNumber AD25 PUSH BC Stash BC on the stack.
AD26 LD C,A Copy the exclusive upper bound into C.
AD27 LD A,R Read the Memory Refresh Register into A.
AD29 LD B,A Use that refresh value as the walk counter in B.
AD2A LD A,C Restore the exclusive upper bound into A.
Count down inside the limit; when it wraps, reload the original bound from C.
GenerateRandomNumber_Loop AD2B DEC A Decrease the running value in A by one.
AD2C JR NZ,GenerateRandomNumber_Next Jump to GenerateRandomNumber_Next if the running value is not zero.
AD2E LD A,C Reload the exclusive upper bound from C into A.
GenerateRandomNumber_Next AD2F DJNZ GenerateRandomNumber_Loop Decrease the walk counter by one and loop back to GenerateRandomNumber_Loop until the refresh count is spent.
AD31 DEC A Decrease the running value in A by one for the final result.
AD32 POP BC Restore BC from the stack.
AD33 RET Return.
View the equivalent code in;
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