MSP430 Energy Library+Reactive power measurement phase shift of 90 deg?

MSP430 Energy Library code：

Calculate reactive code：

I_live_sample = phase->current[0].I_history[0][0];

corrected = (Q1_15_mul(phase->V_history[(phase->V_history_index –phase

->current[0].quadrature_correction[use_stage].step - 1) & V_HISTORY_MASK], phase

->current[0].quadrature_correction[use_stage].fir_beta) >> 1)+

(phase->V_history[(phase->V_history_index - phase->current[0].quadrature_correction[use_stage].step) &V_HISTORY_MASK]>>1);

accum48(phase->current[0].P_reactive_accum[use_stage], imul16(corrected, I_live_sample));

main(reactive power) code：

x = div_sh48(phase->current[0].P_reactive_accum_logged[0], 27 - 2*ADC_BITS, phase->sample_count_logged);

i = phase_nv->current[0].P_scale_factor[0];

i = Q1_15_mul(i, phase->current[0].quadrature_correction[0].fir_gain);

x = mul48(x, i);

Does anyone know how the reactive power calculation is processed?

Reactive power measurement phase shift of 90 deg, i don't know?

please

does anyone know how the reactive power calculation is processed?