| // Copyright 2022 Google LLC. |
| // SPDX-License-Identifier: Apache-2.0 |
| |
| // ported from: https://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel |
| fn popcount(v: u8) -> u8 { |
| let v = v - ((v >> 1) & u8:0x55); |
| let v = (v & u8:0x33) + ((v >> 2) & u8:0x33); |
| (v + (v >> 4) & u8:0x0F) |
| } |
| |
| #[test] |
| fn popcount_test() { |
| let _= assert_eq(popcount(u8:0b0000_0000), u8:0); |
| let _= assert_eq(popcount(u8:0b0000_0001), u8:1); |
| let _= assert_eq(popcount(u8:0b1111_0000), u8:4); |
| let _= assert_eq(popcount(u8:0b0101_0101), u8:4); |
| let _= assert_eq(popcount(u8:0b1111_1111), u8:8); |
| _ |
| } |
| |
| pub fn user_module(io_in: u8) -> u8 { |
| popcount(io_in) |
| } |
