Franz Pucher / TINF

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Bitmanipulationen Grundlegend

Inhalt

Kopiere das Programm in den mbed-Simulator und ändere die globale Variable shift und kontrolliere die vier blauen Leds.

bit-shift.cpp

#include "mbed.h"
 
DigitalOut led1(LED1);
DigitalOut led2(LED2);
DigitalOut led3(LED3);
DigitalOut led4(LED4);
 
uint8_t pos = 0;
uint8_t shift = 3;          // change the value between 0 and 3
 
int main() {
    while (1) {
        pos = (1 << shift); // shift left
        printf("%d\n", pos);
        if(pos == 0b00001000)
            led4 = !led4;
        if(pos == 0b00000100)
            led3 = !led3;
        if(pos == 0b00000010)
            led2 = !led2;
        if(pos == 0b00000001)
            led1 = !led1;
        wait_ms(500);
    }
}

Maskierung

Baue den folgenden Code in ein Programm ein und verwende an Stelle der konstanten Werte Variable.

uint8_t mask = 0x0f;   //00001111b
uint8_t value = 0x55;  //01010101b
value = mask & value;

Beispiel für das Extrahieren der 4 Bytes aus einer 32 Bit Integer Zahl (& und >>):

uint32_t value = 0x01020304            	//Example value
uint32_t byte1 = (value >> 24);			//0x01020304 >> 24 is 0x01 so
                                        //no masking is necessary
uint32_t byte2 = (value >> 16) & 0xff;  //0x01020304 >> 16 is 0x0102 so
                                        //we must mask to get 0x02
uint32_t byte3 = (value >> 8)  & 0xff;  //0x01020304 >> 8 is 0x010203 so
                                        //we must mask to get 0x03
uint32_t byte4 = value & 0xff;          //here we only mask, no shifting
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