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Add benchmarks for [u8]::make_ascii_uppercase

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SimonSapin committed Mar 18, 2019
1 parent 0f88167 commit 8740d5d171fbb2fc9a12e46ecda32a0124badb46
Showing with 173 additions and 0 deletions.
  1. +172 −0 src/libcore/benches/
  2. +1 −0 src/libcore/benches/
@@ -0,0 +1,172 @@
// Lower-case ASCII 'a' is the first byte that has its highest bit set after wrap-adding 0x1F:
// b'a' + 0x1F == 0x80 == 0b1000_0000
// b'z' + 0x1F == 0x98 == 0b10011000
// Lower-case ASCII 'z' is the last byte that has its highest bit unset after wrap-adding 0x05:
// b'a' + 0x05 == 0x66 == 0b0110_0110
// b'z' + 0x05 == 0x7F == 0b0111_1111
// … except for 0xFB to 0xFF, but those are in the range of bytes that have the highest bit
// unset again after adding 0x1F.
// So `(byte + 0x1f) & !(byte + 5)` has its highest bit set
// iff `byte` is a lower-case ASCII letter.
// Lower-case ASCII letters all have the 0x20 bit set.
// (Two positions right of 0x80, the highest bit.)
// Unsetting that bit produces the same letter, in upper-case.
// Therefore:
fn branchless_to_ascii_upper_case(byte: u8) -> u8 {
byte &
byte.wrapping_add(0x1f) &
!byte.wrapping_add(0x05) &
) >> 2

macro_rules! benches {
($( fn $name: ident($arg: ident: &mut [u8]) $body: block )+) => {
benches!(mod short SHORT $($name $arg $body)+);
benches!(mod medium MEDIUM $($name $arg $body)+);
benches!(mod long LONG $($name $arg $body)+);

(mod $mod_name: ident $input: ident $($name: ident $arg: ident $body: block)+) => {
mod $mod_name {
use super::*;

fn $name(bencher: &mut Bencher) {
bencher.bytes = $input.len() as u64;
bencher.iter(|| {
let mut vec = $input.as_bytes().to_vec();
let $arg = &mut vec[..];

use test::black_box;
use test::Bencher;

benches! {
fn bench00_alloc_only(_bytes: &mut [u8]) {}

fn bench01_black_box_read_each_byte(bytes: &mut [u8]) {
for byte in bytes {

fn bench02_lookup(bytes: &mut [u8]) {
for byte in bytes {
*byte = ASCII_UPPERCASE_MAP[*byte as usize]

fn bench03_branch_and_subtract(bytes: &mut [u8]) {
for byte in bytes {
*byte = if b'a' <= *byte && *byte <= b'z' {
*byte - b'a' + b'A'
} else {

fn bench04_branch_and_mask(bytes: &mut [u8]) {
for byte in bytes {
*byte = if b'a' <= *byte && *byte <= b'z' {
*byte & !0x20
} else {

fn bench05_branchless(bytes: &mut [u8]) {
for byte in bytes {
*byte = branchless_to_ascii_upper_case(*byte)

fn bench06_libcore(bytes: &mut [u8]) {

macro_rules! repeat {
($s: expr) => { concat!($s, $s, $s, $s, $s, $s, $s, $s, $s, $s) }

const SHORT: &'static str = "Alice's";
const MEDIUM: &'static str = "Alice's Adventures in Wonderland";
const LONG: &'static str = repeat!(r#"
La Guida di Bragia, a Ballad Opera for the Marionette Theatre (around 1850)
Alice's Adventures in Wonderland (1865)
Phantasmagoria and Other Poems (1869)
Through the Looking-Glass, and What Alice Found There (includes "Jabberwocky" and "The Walrus and the Carpenter") (1871)
The Hunting of the Snark (1876)
Rhyme? And Reason? (1883) – shares some contents with the 1869 collection, including the long poem "Phantasmagoria"
A Tangled Tale (1885)
Sylvie and Bruno (1889)
Sylvie and Bruno Concluded (1893)
Pillow Problems (1893)
What the Tortoise Said to Achilles (1895)
Three Sunsets and Other Poems (1898)
The Manlet (1903)[106]

const ASCII_UPPERCASE_MAP: [u8; 256] = [
0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
b' ', b'!', b'"', b'#', b'$', b'%', b'&', b'\'',
b'(', b')', b'*', b'+', b',', b'-', b'.', b'/',
b'0', b'1', b'2', b'3', b'4', b'5', b'6', b'7',
b'8', b'9', b':', b';', b'<', b'=', b'>', b'?',
b'@', b'A', b'B', b'C', b'D', b'E', b'F', b'G',
b'H', b'I', b'J', b'K', b'L', b'M', b'N', b'O',
b'P', b'Q', b'R', b'S', b'T', b'U', b'V', b'W',
b'X', b'Y', b'Z', b'[', b'\\', b']', b'^', b'_',

b'A', b'B', b'C', b'D', b'E', b'F', b'G',
b'H', b'I', b'J', b'K', b'L', b'M', b'N', b'O',
b'P', b'Q', b'R', b'S', b'T', b'U', b'V', b'W',
b'X', b'Y', b'Z',

b'{', b'|', b'}', b'~', 0x7f,
0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,
0x88, 0x89, 0x8a, 0x8b, 0x8c, 0x8d, 0x8e, 0x8f,
0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97,
0x98, 0x99, 0x9a, 0x9b, 0x9c, 0x9d, 0x9e, 0x9f,
0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7,
0xa8, 0xa9, 0xaa, 0xab, 0xac, 0xad, 0xae, 0xaf,
0xb0, 0xb1, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6, 0xb7,
0xb8, 0xb9, 0xba, 0xbb, 0xbc, 0xbd, 0xbe, 0xbf,
0xc0, 0xc1, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7,
0xc8, 0xc9, 0xca, 0xcb, 0xcc, 0xcd, 0xce, 0xcf,
0xd0, 0xd1, 0xd2, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7,
0xd8, 0xd9, 0xda, 0xdb, 0xdc, 0xdd, 0xde, 0xdf,
0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7,
0xe8, 0xe9, 0xea, 0xeb, 0xec, 0xed, 0xee, 0xef,
0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7,
0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff,

@@ -5,6 +5,7 @@ extern crate core;
extern crate test;

mod any;
mod ascii_case;
mod char;
mod hash;
mod iter;

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