Minor re-arrangement for compatibiility.

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/bench/bench_patprep.rs

@@ -1,11 +1,13 @@
-use squozen::prepare_pattern::prepare_pattern;
+use squozen::prepare_pattern::prepare_pattern_raw;
 
 const COUNT: usize = 5 * 1000 * 1000 * 100;
 
 fn main() {
     let mut end = COUNT;
+    let mut dest = Vec::<u8>::with_capacity(100);
     while end > 0 {
-        let _g = prepare_pattern(b"/foo/bar/whatever[0-9]*");
+        dest.clear();
+        prepare_pattern_raw(b"/foo/bar/whatever[0-9]*", &mut dest);
         end = end - 1;
     }
 }

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++) {

crates/squozen/src/prepare_pattern.rs

@@ -28,7 +28,13 @@ where
 }
 
 pub fn prepare_pattern(name: &[u8]) -> Vec<u8> {
-    let mut eol = name.len();
+    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 eol = name.len();
     if eol == 0 {
         panic!("Library error - This function should never be called with an empty string.")
     }
@@ -36,17 +42,19 @@ pub fn prepare_pattern(name: &[u8]) -> Vec<u8> {
     // After this point, eol always points to the index from where we want to
     // stop, not to the character beyond that.
 
-    eol = hunt(name, eol - 1, 0, |&c| c != b'*' && c != b'?');
+    let mut eol = hunt(name, eol - 1, 0, |&c| c != b'*' && c != b'?');
     if name[eol] == b']' {
         eol = hunt(&name, eol - 1, 0, |&c| c == b'[');
         eol = if eol > 0 { eol - 1 } else { 0 }
     }
 
     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]);
     }
 }