[HP35s] Fastest way to increment a variable

[fred_76]

Hello

There are several ways to increment an integer variable by 1. But some are faster than others.

First of all, the "most common one", which is the base time :

Code:


1
STO+V

=> takes 37 ms and 2 lines of code

With the slow equations :

Code:


EQN 1+V►V

=> takes 125 ms (3.4x slower) but only 1 line of code

The ugly one :

Code:


RCL V
1
+
STO V

=> takes 49 ms (1.3x slower) and 4 lines of code

After an idea of Csaba, the counter is stored in the stat pile (to be recalled by the function [SUMS][n]) :

Code:


CLSTK
Σ+

=> takes 37 ms (as fast as the base case), and 2 lines of code, but requires the use of the stat pile and clears the xyzt pile

Note that the CLSTK is required for time effectiveness as Σ+ runs faster when the registers x=y=0. If you want to be more friendly with the pile, use CLx instead of CLSTK, you will loose about 2 ms but it will be better for the pile's health !

If you don't use CLSTK or CLx, the execution time of Σ+ with x,y<>0,0 will take about 42 ms.

The official alternative :

Code:


ISG V
Dummy line

=> takes 31 ms (1.2x faster) and 2 lines of code

The unexpected but quite fast one :

Code:


RCL V
NOT
+/-
STO V

=> only takes 22 ms (1.7x faster) but 4 lines of code, and only works with integers

If you agree to store constants in variables (here 1 in N), then :

Code:


RCL N
STO+V

=> only takes 14 ms (2.6x faster) and 2 lines of code, but requires to store the constant 1 in a variable

These are some ways to optimize the execution time on slow machines, like the HP35s, especially if those instructions are repeated hundreds of times.

As a conclusion :
RCL N | STO+V = 14 ms
RCL V | NOT | +/- | STO V = 22 ms
ISG V | Dummy line = 31 ms
CLSTK | Σ+ = 37 ms
1 | STO+V = 37 ms
CLx | Σ+ = 39 ms
Σ+ = 42 ms
RCL V | 1 | + | STO V = 49 ms
EQN 1+V►V = 125 ms

Fred