How the vertical bar is used in following code

Question

I was decoding a c++ code and did not understand why is the vertical bar is used in the 6th line.

void build(int id, int l, int r) {
  if (l == r) {
    sum[id] = a[l];
    return;
  }
  int mid = (l + r) >> 1;
  build(id << 1, l, mid);
  build(id << 1 | 1, mid + 1, r); /*what operation does vertical
                                 bar perform with bitwise operator*/
  sum[id] = max(sum[id << 1], sum[id << 1 | 1]);
}

Before asking here, do some research. Maybe check the [reference](https://en.cppreference.com/w/cpp/language/operator_arithmetic) — Aykhan Hagverdili, Jul 21 '19 at 04:47
Possible duplicate of [What are bitwise operators?](https://stackoverflow.com/questions/276706/what-are-bitwise-operators) — Aykhan Hagverdili, Jul 21 '19 at 04:49

john · Answer 1 · 2019-07-21T04:37:35.120

2

This code

build(id<<1,l,mid);
build(id<<1|1,mid+1,r);

is equivalent to

build(2*id, l, mid);
build(2*id+1, mid+1, r);

The only difference is the first has been written by someone who thinks (wrongly) that it's more efficient than the second. A good programmer would prefer the second because it's easier to understand.

edited Jul 21 '19 at 04:37

answered Jul 21 '19 at 04:19

john

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Most programmers would prefer the first, because it is easier to understand -- shifting in a 1 bit. Mixing shift and add is more complex and harder to understand. – Chris Dodd Jul 21 '19 at 04:44
1

@ChrisDodd I didn't mix shift and add. – john Jul 21 '19 at 04:47

score 1 · Answer 2 · answered Jul 21 '19 at 04:11

1

The | is a bitwise or. It takes two numbers as operands and does OR on each bit of the two numbers.

For example, consider the ORing of the following tow bit patterns: 00011010 | 10000111 = 10011111

answered Jul 21 '19 at 04:11

ManLaw

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How the vertical bar is used in following code

2 Answers2