#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
/* Print bits of a 32-bit integer */
void printBits(uint32_t x, const char *label) {
int i;
printf("%s: ", label);
for (i = 31; i >= 0; --i) {
printf("%u", (x >> i) & 1u);
}
printf("\n");
}
/* Clear bits in range [l, r] inclusive (0 = least significant bit) */
uint32_t clearBits(uint32_t x, int l, int r) {
if (l < 0 || r > 31 || l > r) {
fprintf(stderr, "Invalid bit range\n");
exit(EXIT_FAILURE);
}
/* maskLeft:
Create a mask with 1s above bit r and 0s from bit r down to 0.
Example: r = 5 → maskLeft = 11111111 11111111 11111111 11000000
*/
uint32_t maskLeft = ~0u << (r + 1);
printBits(maskLeft, "maskLeft ");
/* maskRight:
Create a mask with 1s below bit l and 0s from bit l upward.
Example: l = 3 → maskRight = 00000000 00000000 00000000 00000111
*/
uint32_t maskRight = (1u << l) - 1;
printBits(maskRight, "maskRight");
/* Combine both masks:
maskLeft keeps bits above r.
maskRight keeps bits below l.
The range [l, r] becomes 0s.
*/
uint32_t mask = maskLeft | maskRight;
printBits(mask, "mask ");
return x & mask;
}
int main(void) {
uint32_t value = 0b11111100111111001111110011111100;
int l = 3; /* start bit */
int r = 10; /* end bit */
uint32_t result = clearBits(value, l, r);
printBits(value, "Before ");
printBits(result, "After ");
return 0;
}
/*
run:
maskLeft : 11111111111111111111100000000000
maskRight: 00000000000000000000000000000111
mask : 11111111111111111111100000000111
Before : 11111100111111001111110011111100
After : 11111100111111001111100000000100
*/
