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Commit 7a261d7

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feat: add binary count trailing zeros algorithm (TheAlgorithms#972)
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‎DIRECTORY.md‎

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* [Reverse Bits](https://github.com/TheAlgorithms/Rust/blob/master/src/bit_manipulation/reverse_bits.rs)
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* [Sum of Two Integers](https://github.com/TheAlgorithms/Rust/blob/master/src/bit_manipulation/sum_of_two_integers.rs)
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* [Swap Odd and Even Bits](https://github.com/TheAlgorithms/Rust/blob/master/src/bit_manipulation/swap_odd_even_bits.rs)
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* [Trailing Zeros](https://github.com/TheAlgorithms/Rust/blob/master/src/bit_manipulation/binary_count_trailing_zeros.rs)
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* [Two's Complement](https://github.com/TheAlgorithms/Rust/blob/master/src/bit_manipulation/twos_complement.rs)
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* Ciphers
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* [AES](https://github.com/TheAlgorithms/Rust/blob/master/src/ciphers/aes.rs)
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/// Counts the number of trailing zeros in the binary representation of a number
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///
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/// # Arguments
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///
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/// * `num` - The input number
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///
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/// # Returns
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///
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/// The number of trailing zeros in the binary representation
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///
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/// # Examples
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///
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/// ```
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/// use the_algorithms_rust::bit_manipulation::binary_count_trailing_zeros;
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///
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/// assert_eq!(binary_count_trailing_zeros(25), 0);
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/// assert_eq!(binary_count_trailing_zeros(36), 2);
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/// assert_eq!(binary_count_trailing_zeros(16), 4);
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/// assert_eq!(binary_count_trailing_zeros(58), 1);
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/// ```
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pub fn binary_count_trailing_zeros(num: u64) -> u32 {
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if num == 0 {
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return 0;
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}
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num.trailing_zeros()
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}
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/// Alternative implementation using bit manipulation
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///
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/// Uses the bit manipulation trick: log2(num & -num)
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///
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/// # Examples
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///
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/// ```
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/// // This function uses bit manipulation: log2(num & -num)
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/// // where num & -num isolates the rightmost set bit
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/// # fn binary_count_trailing_zeros_bitwise(num: u64) -> u32 {
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/// # if num == 0 { return 0; }
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/// # let rightmost_set_bit = num & (num.wrapping_neg());
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/// # 63 - rightmost_set_bit.leading_zeros()
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/// # }
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/// assert_eq!(binary_count_trailing_zeros_bitwise(25), 0);
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/// assert_eq!(binary_count_trailing_zeros_bitwise(36), 2);
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/// assert_eq!(binary_count_trailing_zeros_bitwise(16), 4);
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/// ```
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#[allow(dead_code)]
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pub fn binary_count_trailing_zeros_bitwise(num: u64) -> u32 {
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if num == 0 {
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return 0;
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}
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let rightmost_set_bit = num & (num.wrapping_neg());
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63 - rightmost_set_bit.leading_zeros()
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn test_basic_cases() {
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assert_eq!(binary_count_trailing_zeros(25), 0);
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assert_eq!(binary_count_trailing_zeros(36), 2);
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assert_eq!(binary_count_trailing_zeros(16), 4);
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assert_eq!(binary_count_trailing_zeros(58), 1);
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assert_eq!(binary_count_trailing_zeros(4294967296), 32);
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}
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#[test]
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fn test_zero() {
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assert_eq!(binary_count_trailing_zeros(0), 0);
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}
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#[test]
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fn test_powers_of_two() {
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assert_eq!(binary_count_trailing_zeros(1), 0);
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assert_eq!(binary_count_trailing_zeros(2), 1);
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assert_eq!(binary_count_trailing_zeros(4), 2);
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assert_eq!(binary_count_trailing_zeros(8), 3);
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assert_eq!(binary_count_trailing_zeros(1024), 10);
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}
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#[test]
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fn test_bitwise_vs_builtin() {
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// Test that bitwise implementation matches built-in trailing_zeros()
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let test_cases = vec![
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0,
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1,
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2,
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3,
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4,
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5,
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6,
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7,
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8,
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16,
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25,
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36,
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58,
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64,
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100,
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128,
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256,
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512,
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1024,
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4294967296,
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u64::MAX - 1,
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u64::MAX,
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];
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for num in test_cases {
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assert_eq!(
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binary_count_trailing_zeros(num),
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binary_count_trailing_zeros_bitwise(num),
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"Mismatch for input: {num}"
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);
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}
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}
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}

‎src/bit_manipulation/mod.rs‎

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mod binary_coded_decimal;
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mod binary_count_trailing_zeros;
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mod counting_bits;
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mod find_previous_power_of_two;
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mod highest_set_bit;
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mod twos_complement;
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pub use self::binary_coded_decimal::binary_coded_decimal;
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pub use self::binary_count_trailing_zeros::binary_count_trailing_zeros;
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pub use self::counting_bits::count_set_bits;
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pub use self::find_previous_power_of_two::find_previous_power_of_two;
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pub use self::highest_set_bit::find_highest_set_bit;

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