Possible simplication (or error) of sx127x/sx126x frequency to pll step calculation

[plaes]

When staring at the sx127x method of calculation PLL step from frequency, I spotted that resulting value for steps_fraq will always be 0:

SWL2001/lbm_lib/smtc_modem_core/radio_drivers/sx127x_driver/src/sx127x.c

Lines 1839 to 1841 in 0ad056a

	// Get integer and fractional parts of the frequency computed with a PLL step scaled value
	steps_int = freq_in_hz / SX127X_PLL_STEP_SCALED;
	steps_frac = freq_in_hz - ( steps_int * SX127X_PLL_STEP_SCALED );

Proof:

steps_fraq = freq_in_hz - ( steps_int * SX127X_PLL_STEP_SCALED );
 // substitute steps_int with its expression:
steps_freq = freq_in_hz - ((freq_in_hz / SX127X_PLL_STEP_SCALED) * SX127X_PLL_STEP_SCALED);
// (x / SX127X_PLL_STEP_SCALED) * SX127X_PLL_STEP_SCALED == x
steps_freq = freq_in_hz - freq_in_hz;
steps_freq = 0;

This would also allow simplifying the return expression to

return (steps_int << SX127X_PLL_STEP_SHIFT_AMOUNT) +  (( SX127X_PLL_STEP_SCALED >> 1 ) / SX127X_PLL_STEP_SCALED );

And after some tests we can drop off the second term which is 0 ending up with just steps_int << SX127X_PLL_STEP_SHIFT_AMOUNT

Update: Same simplification can be applied in the sx126x driver as well:

SWL2001/lbm_lib/smtc_modem_core/radio_drivers/sx126x_driver/src/sx126x.c

Lines 1257 to 1265 in 0ad056a

	// Get integer and fractional parts of the frequency computed with a PLL step scaled value
	steps_int = freq_in_hz / SX126X_PLL_STEP_SCALED;
	steps_frac = freq_in_hz - ( steps_int * SX126X_PLL_STEP_SCALED );
	// Apply the scaling factor to retrieve a frequency in Hz (+ ceiling)
	return ( steps_int << SX126X_PLL_STEP_SHIFT_AMOUNT ) +
	( ( ( steps_frac << SX126X_PLL_STEP_SHIFT_AMOUNT ) + ( SX126X_PLL_STEP_SCALED >> 1 ) ) /
	SX126X_PLL_STEP_SCALED );
	}

[opeyrard]

Hi,
(freq_in_hz / SX126X_PLL_STEP_SCALED) x SX126X_PLL_STEP_SCALED is not equal to freq_in_hz in integer in C.
Many thanks,
Best regards,