part: `SearchSeq` now uses capacity-extended-switching between forward and backward searching (like `SearchPar` does.)

part: Fixed bug where `cap` may grow above buffer-halve length (in `SearchSeq` and `SearchPar`.)

part: TODO: Added test skeleton for testing `SearchSeq` and `SearchPar` correctness. Implement these tests!

Fortune for reverse's current commit: Small blessing − 小吉

src/part.rs

@@ -32,14 +32,55 @@ impl MidpointFBSearcher<u8> for SearchSeq
 
     #[inline] 
     fn search_combined<'a>(&self, haystack: &'a [u8], begin: usize, needle: u8) -> Option<&'a u8> {
+	let max_cap = match get_max_pivot_search_area(haystack.len() > (DEFAULT_PIVOT_MAX_SEARCH_AREA * DEFAULT_MEM_DETECT_HUGE_SIZE_PAGES)){ // Assume huge-page memory if len is larger than 4 pages.
+		
+		// On debug builds, cap search area to one system page only.
+		_ignore if cfg!(debug_assertions) && (*REAL_PAGE_SIZE) > 0 =>
+		// SAFETY: We have checked if `*REAL_PAGE_SIZE` is non-zero above.
+		    Some(unsafe { NonZeroUsize::new_unchecked(*REAL_PAGE_SIZE as usize) }),
+		// Otherwise, use the detected value.
+		cap => cap,
+	};
+
+	
 	match haystack.split_at(begin) {
 	    ([], []) => None,
 	    ([], x) => self.search_forward(x, needle),
 	    (x, []) => self.search_backward(x, needle),
-	    
-	    (x, y) => {
+
+	    // If both the buffers are lower than `max_cap`, just do the entire operation on each
+	    (x, y) if max_cap.map(|max| x.len() <= max.get() && y.len() <= max.get()).unwrap_or(false) => {
 		self.search_forward(y, needle)?;
 		self.search_backward(x, needle)
+	    },
+	    
+	    (mut x, mut y) => {
+		let len = std::cmp::min(x.len(), y.len());
+		let mut cap = std::cmp::min(len, DEFAULT_PIVOT_MAX_SEARCH_AREA);
+
+		while cap <= len {
+		    // If cap is too large for one (or more) of the buffers, truncate it.
+		    if cap > y.len() || cap > x.len() {
+			cap = std::cmp::min(y.len(), x.len());
+		    }
+		    
+		    // Search forwards in `y`. (up to `cap`)
+		    if let Some(y) = self.search_forward(&y[..cap], needle) {
+			return Some(y);
+		    }
+		    // Search backwards in `x`. (down to `cap`)
+		    if let Some(x) = self.search_backward(&x[(x.len()-cap)..], needle) {
+			return Some(x);
+		    }
+
+		    // Cut out `cap` bytes from the start of forwards
+		    y = &y[cap..];
+		    // Cut out `cap` bytes from the end of backwards.
+		    x = &x[..cap];
+		    // Grow `cap` by 1 ^2 (not passing `max_cap` if there is one set.)
+		    cap = max_cap.map(|max| std::cmp::min(max.get(), cap << 1)).unwrap_or_else(|| cap << 1);
+		}
+		None
 	    }
 	}
     }
@@ -193,15 +234,24 @@ impl MidpointFBSearcher<u8> for SearchPar
 		// Otherwise, use the detected value.
 		cap => cap,
 	    };
+	    // Cap the cap to `max_cap` if there is a max cap.
+	    let cap = if let Some(max) = max_cap.as_ref() {
+		    std::cmp::min(max.get(), self.cap_start)
+		} else {
+		    self.cap_start
+		};
 
 	    let forward = if hf.len() > 0 {
-		let cap = self.cap_start;
+		let cap = cap;
 		let sf = &self;
 		let complete = &complete;
 		Some(s.spawn(move || -> Option<_> {
 		    let mut cap = std::cmp::min(cap, hf.len());
 		    let len = hf.len();
 		    while cap <= len {
+			// If `cap` is larger than the buffer `hf`, truncate it.
+			cap = std::cmp::min(cap, hf.len());
+			// Search forward in `hf` up to `cap` bytes.
 			if let /*v @ */Some(x) = sf.search_forward(&hf[..cap], needle) {
 			    complete.store(true);
 			    //complete.call_once(|| complete_val = true);
@@ -220,13 +270,16 @@ impl MidpointFBSearcher<u8> for SearchPar
 		None
 	    };
 	    let backward = if hb.len() > 0 {
-		let cap = self.cap_start;
+		let cap = cap;
 		let sf = &self;
 		let complete = &complete;
 		Some(s.spawn(move || -> Option<_> {
 		    let mut cap = std::cmp::min(cap, hb.len());
 		    let len = hb.len();
 		    while cap <= len {
+			// If `cap` is larger than the buffer `hb`, truncate it.
+			cap = std::cmp::min(cap, hb.len());
+			// Search backwards in `hb` up to `cap` bytes.
 			if let /*v @ */Some(x) = sf.search_backward(&hb[(hb.len()-cap)..], needle) {
 			    complete.store(true);
 			    //complete.call_once(|| complete_val = true);
@@ -266,3 +319,36 @@ where S: MidpointFBSearcher<u8>
 //XXX: Should we add a `SearchAsync`? Or an impl for SearchPar that uses already-spawned threads? TODO: It would be best if we could re-use extant threads instead of spawning two on each partition...
 
 //Parallel (feature="threads") byte area partition-on-nearest-newline-to-halve impl, and non-parallel (default) impl. These impls can differ in their desired depths of partitioning (using parallel impls should balance num of partitions to num of logical cpus & input(/desired chunk) size.)
+
+//TODO: Add tests for `Search{Seq,Par}` partitioning methods.
+#[cfg(test)]
+mod test
+{
+    #[test]
+    fn partition_seq()
+    {
+	todo!("Test `SearchSeq` sequential partition searcher")
+    }
+    
+    #[cfg(feature="threads")] 
+    #[test]
+    fn partition_par_heavy()
+    {
+	todo!("Test `SearchPar` parallel partition searcher")
+    }
+
+    //TODO: Thread-reusing parallel `MidpointFBSearcher` (SearchSeq is thread-*spawning*; heavy.) This may require we use async and tasks. If it does, we should also create a `SearchAsync` partitioner (XXX: MidpointFBSearcher is currently a synchonous-only interface; a pure-async pivot finder may require a refactor.)
+	#[cfg(all(feature="threads-async", feature = "threads"))] 
+	#[test]
+	fn partition_par_light()
+	{
+	    unimplemented!("A light (thread-*reusing*) parallel searcher has not yet been implemented")
+	}
+
+	#[cfg(feature="threads-async")] 
+	#[/*tokio::*/test]
+	fn partition_par_async()
+	{
+	    unimplemented!("A pure async parallel searcher has not yet been implemented")
+	}
+}