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June 12, 2021 01:01
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Test popcnt implementations
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use std::time::Instant; | |
use std::thread::sleep; | |
use std::time::Duration; | |
macro_rules! do_timing { | |
($name:expr, $body:expr) => { | |
{ | |
let from_time = Instant::now(); | |
let value = { | |
$body | |
}; | |
let duration = from_time.elapsed(); | |
eprintln!("timing: {:>7} ms for {} result {}", duration.as_millis(), $name, value); | |
} | |
} | |
} | |
fn pause_for_thermals() { | |
sleep(Duration::from_secs(5)); | |
} | |
#[inline(always)] | |
fn count_bitwise(val: u32) -> u32 { | |
let mut x = val; | |
x = (x & 0x55555555) + ((x >> 1) & 0x55555555); | |
x = (x & 0x33333333) + ((x >> 2) & 0x33333333); | |
x = (x & 0x0f0f0f0f) + ((x >> 4) & 0x0f0f0f0f); | |
x = (x & 0x00ff00ff) + ((x >> 8) & 0x00ff00ff); | |
x = (x & 0x0000ffff) + (x >> 16); | |
x | |
} | |
#[inline(always)] | |
fn count_lookup(val: u32, table: &[u32]) -> u32 { | |
let bytes = val.to_ne_bytes(); | |
table[bytes[0] as usize] + | |
table[bytes[1] as usize] + | |
table[bytes[2] as usize] + | |
table[bytes[3] as usize] | |
} | |
pub fn main() { | |
let mut table: Vec<u32> = Vec::with_capacity(256); | |
for n in (0 as u32)..256 { | |
table.push(n.count_ones()); | |
} | |
pause_for_thermals(); | |
do_timing!("validate ", { | |
let mut result: u64 = 0; | |
for n in 0..u32::MAX { | |
let truth = n.count_ones(); | |
result += truth as u64; | |
assert_eq!(count_bitwise(n), truth); | |
assert_eq!(count_lookup(n, &table), truth); | |
} | |
result | |
}); | |
pause_for_thermals(); | |
do_timing!("count_ones ", { | |
let mut result: u64 = 0; | |
for n in 0..u32::MAX { | |
result += n.count_ones() as u64; | |
} | |
result | |
}); | |
pause_for_thermals(); | |
do_timing!("count_bitwise", { | |
let mut result: u64 = 0; | |
for n in 0..u32::MAX { | |
result += count_bitwise(n) as u64; | |
} | |
result | |
}); | |
pause_for_thermals(); | |
do_timing!("count_lookup ", { | |
let mut result: u64 = 0; | |
for n in 0..u32::MAX { | |
result += count_lookup(n, &table) as u64; | |
} | |
result | |
}); | |
} |
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