From 40811151abf12dfd308223add0705a0776e51559 Mon Sep 17 00:00:00 2001
From: "Elf M. Sternberg" <elf.sternberg@gmail.com>
Date: Sun, 13 Nov 2022 12:33:34 -0800
Subject: [PATCH] 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.
---
 crates/squozen/docs/patprep/bench_patprep.c |  2 +-
 crates/squozen/src/prepare_pattern.rs       | 18 +++++++++++++-----
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/crates/squozen/docs/patprep/bench_patprep.c b/crates/squozen/docs/patprep/bench_patprep.c
index ab36738..37b033d 100644
--- a/crates/squozen/docs/patprep/bench_patprep.c
+++ b/crates/squozen/docs/patprep/bench_patprep.c
@@ -1,6 +1,6 @@
 #include "patprep.h"
 
-const int count = 5 * 1000 * 1000 * 1000;
+const int count = 5 * 1000 * 1000 * 100;
 
 void main() {
   for (int i = 0; i <= count; i++) {
diff --git a/crates/squozen/src/prepare_pattern.rs b/crates/squozen/src/prepare_pattern.rs
index 6966372..77d021d 100644
--- a/crates/squozen/src/prepare_pattern.rs
+++ b/crates/squozen/src/prepare_pattern.rs
@@ -28,6 +28,12 @@ where
 }
 
 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();
     if eol == 0 {
         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 {
-        return if GLOBCHARS.contains(&name[0]) {
-            vec![b'/']
+        if GLOBCHARS.contains(&name[0]) {
+            dest.push(b'/');
+            return;
         } else {
-            vec![name[0]]
+            dest.push(name[0]);
+            return;
         };
     }
 
@@ -57,9 +65,9 @@ pub fn prepare_pattern(name: &[u8]) -> Vec<u8> {
         start
     };
     if start > eol {
-        vec![b'/']
+        dest.push(b'/');
     } else {
-        name[start..eol + 1].to_vec()
+        dest.extend_from_slice(&name[start..eol + 1]);
     }
 }