Hi,
I'm optimising my code, mainly for size. Knowing how much better
code SDCC creates for global variables I made an interesting comparison
which I thought I share here, see code below.
Interestingly the code (bar4) that four times expands the whole
'get position' calculation is smaller (585 < 622) than the more
conventionally coded subroutine (bar5) based version.
And, maybe not surprisingly, it is about four times faster.
(The execution times are of course estimate based on code
size and the execution path assumption).
Without testing conventional wisdom would have led me to
believe that the macro version would be much bigger than
the subroutine based one.
br Kusti
stepper_state_t g_stepper_states[4];
#define GET_POSITION(i) \
(g_stepper_states[i].last_dir)?\
( g_stepper_states[i].position + (g_stepper_states[i].last_steps -
g_stepper_states[i].steps))\
:\
( g_stepper_states[i].position - (g_stepper_states[i].last_steps -
g_stepper_states[i].steps))\
int32_t get_position(uint8_t i) { // bytes 434 cycles ~217
return (g_stepper_states[i].last_dir)?
( g_stepper_states[i].position + (g_stepper_states[i].last_steps -
g_stepper_states[i].steps))
:
( g_stepper_states[i].position - (g_stepper_states[i].last_steps -
g_stepper_states[i].steps));
}
int32_t pos=0;
void bar4() { // bytes 582 cycles ~291
pos=GET_POSITION(0);
pos=GET_POSITION(1);
pos=GET_POSITION(2);
pos=GET_POSITION(3);
}
void bar5() { // bytes 188 cycles 188
pos=get_position(0);
pos=get_position(1);
pos=get_position(2);
pos=get_position(3);
}
// bar 4 = bytes 582 cycles 291
// bar 5 = bytes 622 = 188 + 434 cycles ~1056 = 188 + 4 * 217~
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