Merge pull request #32 from qryxip/internal-bit

Implement `internal_bit`

Author: koba-e964

src/internal_bit.rs

@@ -1 +1,30 @@
+// Skipped:
+//
+// - `bsf` = `__builtin_ctz`: is equivalent to `{integer}::trailing_zeros`
 
+#[allow(dead_code)]
+pub(crate) fn ceil_pow2(n: u32) -> u32 {
+    32 - n.saturating_sub(1).leading_zeros()
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn ceil_pow2() {
+        // https://github.com/atcoder/ac-library/blob/2088c8e2431c3f4d29a2cfabc6529fe0a0586c48/test/unittest/bit_test.cpp
+        assert_eq!(0, super::ceil_pow2(0));
+        assert_eq!(0, super::ceil_pow2(1));
+        assert_eq!(1, super::ceil_pow2(2));
+        assert_eq!(2, super::ceil_pow2(3));
+        assert_eq!(2, super::ceil_pow2(4));
+        assert_eq!(3, super::ceil_pow2(5));
+        assert_eq!(3, super::ceil_pow2(6));
+        assert_eq!(3, super::ceil_pow2(7));
+        assert_eq!(3, super::ceil_pow2(8));
+        assert_eq!(4, super::ceil_pow2(9));
+        assert_eq!(30, super::ceil_pow2(1 << 30));
+        assert_eq!(31, super::ceil_pow2((1 << 30) + 1));
+
+        assert_eq!(32, super::ceil_pow2(u32::max_value()));
+    }
+}