// Print bits of a 32-bit integer
function printBits(x, label) {
// Convert to binary and pad to 32 bits
const bits = (x >>> 0).toString(2).padStart(32, "0");
console.log(`${label}: ${bits}`);
}
// Clear bits in range [l, r] inclusive (0 = least significant bit)
function clearBits(x, l, r) {
if (l < 0 || r > 31 || l > r) {
throw new Error("Invalid bit range");
}
// 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
let maskLeft = (~0 << (r + 1)) >>> 0;
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
let maskRight = ((1 << l) - 1) >>> 0;
printBits(maskRight, "maskRight");
// Combine both masks:
// maskLeft keeps bits above r.
// maskRight keeps bits below l.
// The range [l, r] becomes 0s.
let mask = (maskLeft | maskRight) >>> 0;
printBits(mask, "mask ");
return (x & mask) >>> 0;
}
// Main program
function main() {
let value = 0b11111100111111001111110011111100;
let l = 3; // start bit
let r = 10; // end bit
let result = clearBits(value, l, r);
printBits(value, "Before ");
printBits(result, "After ");
}
main();
/*
run:
maskLeft : 11111111111111111111100000000000
maskRight: 00000000000000000000000000000111
mask : 11111111111111111111100000000111
Before : 11111100111111001111110011111100
After : 11111100111111001111100000000100
*/
