Arduino UNO
IDE 1.8.19

fastShiftIn_test.ino
0.4.0

 8 bits HIGH


Performance - time in us : read()
FastShiftIn1: 12.51
FastShiftIn2: 23.77
       Delta: 11.26


Performance - time in us : read16()
FastShiftIn1: 23.28
FastShiftIn2: 45.78
       Delta: 22.50


Performance - time in us : read24()
FastShiftIn1: 35.54
FastShiftIn2: 70.30
       Delta: 34.76


Performance - time in us : read32()
FastShiftIn1: 46.41
FastShiftIn2: 92.05
       Delta: 45.64


Performance - time in us : readLSBFIRST()
FastShiftIn1: 12.83
FastShiftIn2: 24.77
       Delta: 11.94


Performance - time in us : readMSBFIRST()
FastShiftIn1: 11.38
FastShiftIn2: 21.88
       Delta: 10.50


Performance - time in us : reference shiftIn()
Standard shiftIn1: 108.99
Standard shiftIn2: 217.04
            Delta: 108.05

done...