The C and Rust versions are now comparable.

The C and Rust versions are now comparable, with a memory-reuse and
a memory-safe version for Rust.  The memory-safe version is five times
faster than the C version; the memory-reuse version (technically safe,
but can panic under some very rare circumstances) is ten times faster.

I suspect the reasons for he speedup are strictly in the `for()` loop
in the C version for copying the string, where the Rust version probably
uses memcpy() under the covers to transfer the short string into the
destination.
This commit is contained in:
Elf M. Sternberg 2022-11-13 12:33:34 -08:00
parent 2eab17934c
commit 40811151ab
2 changed files with 14 additions and 6 deletions

View File

@ -1,6 +1,6 @@
#include "patprep.h" #include "patprep.h"
const int count = 5 * 1000 * 1000 * 1000; const int count = 5 * 1000 * 1000 * 100;
void main() { void main() {
for (int i = 0; i <= count; i++) { for (int i = 0; i <= count; i++) {

View File

@ -28,6 +28,12 @@ where
} }
pub fn prepare_pattern(name: &[u8]) -> Vec<u8> { pub fn prepare_pattern(name: &[u8]) -> Vec<u8> {
let mut dest = Vec::with_capacity(116);
prepare_pattern_raw(name, &mut dest);
dest
}
pub fn prepare_pattern_raw(name: &[u8], dest: &mut Vec<u8>) {
let mut eol = name.len(); let mut eol = name.len();
if eol == 0 { if eol == 0 {
panic!("Library error - This function should never be called with an empty string.") panic!("Library error - This function should never be called with an empty string.")
@ -43,10 +49,12 @@ pub fn prepare_pattern(name: &[u8]) -> Vec<u8> {
} }
if eol == 0 { if eol == 0 {
return if GLOBCHARS.contains(&name[0]) { if GLOBCHARS.contains(&name[0]) {
vec![b'/'] dest.push(b'/');
return;
} else { } else {
vec![name[0]] dest.push(name[0]);
return;
}; };
} }
@ -57,9 +65,9 @@ pub fn prepare_pattern(name: &[u8]) -> Vec<u8> {
start start
}; };
if start > eol { if start > eol {
vec![b'/'] dest.push(b'/');
} else { } else {
name[start..eol + 1].to_vec() dest.extend_from_slice(&name[start..eol + 1]);
} }
} }