From 5716ae804d5f1007acfbb0ee4a99bc840c5b982b Mon Sep 17 00:00:00 2001
From: alice pellerin <thealicepellerin@gmail.com>
Date: Sat, 21 Mar 2026 01:10:24 -0500
Subject: [PATCH] jump to selected offset

---
 src/action.rs | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++-
 src/config.rs |  4 ++++
 src/main.rs   |  4 +++-
 3 files changed, 58 insertions(+), 2 deletions(-)

diff --git a/src/action.rs b/src/action.rs
index 2798d38..8e7b2e1 100644
--- a/src/action.rs
+++ b/src/action.rs
@@ -81,6 +81,8 @@ pub enum Action {
 	SplitSelectionsInto7s,
 	SplitSelectionsInto8s,
 	SplitSelectionsInto9s,
+	
+	JumpToSelectedOffset,
 }
 
 // actions that act on the app as a whole, not just one buffer
@@ -171,6 +173,8 @@ impl Buffer {
 			Action::SplitSelectionsInto7s => self.split_selections_into_size(7),
 			Action::SplitSelectionsInto8s => self.split_selections_into_size(8),
 			Action::SplitSelectionsInto9s => self.split_selections_into_size(9),
+			
+			Action::JumpToSelectedOffset => self.jump_to_selected_offset(window_size),
 		}
 		
 		None
@@ -600,12 +604,48 @@ impl Buffer {
 				cursor
 					.range()
 					.step_by(size)
-					.map(|head| Cursor { head, tail: head + size - 1 })
+					.map(|tail| Cursor { head: tail + size - 1, tail })
 			});
 		
 		self.primary_cursor = new_cursors.next().unwrap();
 		self.cursors = new_cursors.collect();
 	}
+	
+	fn jump_to_selected_offset(&mut self, window_size: WindowSize) {
+		if !iter::once(&self.primary_cursor)
+			.chain(&self.cursors)
+			.all(|cursor| {
+				bytes_as_nat(&self.contents[cursor.range()])
+					.is_some_and(|offset| offset < self.contents.len())
+			})
+		{
+			if self.cursors.is_empty() {
+				self.alert_message = Span::from(
+					"selection is not a valid offset"
+				).red();
+			} else {
+				self.alert_message = Span::from(
+					"not all selections are valid offsets"
+				).red();
+			}
+			return;
+		}
+		
+		self.primary_cursor = Cursor::at(
+			bytes_as_nat(&self.contents[self.primary_cursor.range()]).unwrap()
+		);
+		
+		for cursor in &mut self.cursors {
+			*cursor = Cursor::at(
+				bytes_as_nat(&self.contents[cursor.range()]).unwrap()
+			);
+		}
+		
+		self.cursors.sort_by_key(|cursor| cursor.head);
+		
+		self.combine_cursors_if_overlapping();
+		self.clamp_screen_to_primary_cursor(window_size);
+	}
 }
 
 // helpers
@@ -622,3 +662,13 @@ impl Buffer {
 		}
 	}
 }
+
+fn bytes_as_nat(bytes: &[u8]) -> Option<usize> {
+	bytes
+		.iter()
+		.rev() // little-endian
+		.skip_while(|&&byte| byte == 0)
+		.try_fold(usize::default(), |result, &byte| {
+			Some(result.shl_exact(8)? | (byte as usize))
+		})
+}
diff --git a/src/config.rs b/src/config.rs
index c0280f6..ea42a00 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -161,6 +161,8 @@ impl Default for Config {
 					("7".try_into().unwrap(), Action::SplitSelectionsInto7s),
 					("8".try_into().unwrap(), Action::SplitSelectionsInto8s),
 					("9".try_into().unwrap(), Action::SplitSelectionsInto9s),
+					
+					("J".try_into().unwrap(), Action::JumpToSelectedOffset),
 				].into()),
 				(Some(PartialAction::Goto), [
 					("j".try_into().unwrap(), Action::GotoLineStart),
@@ -230,6 +232,8 @@ impl Default for Config {
 					("7".try_into().unwrap(), Action::SplitSelectionsInto7s),
 					("8".try_into().unwrap(), Action::SplitSelectionsInto8s),
 					("9".try_into().unwrap(), Action::SplitSelectionsInto9s),
+					
+					("J".try_into().unwrap(), Action::JumpToSelectedOffset),
 				].into()),
 				(Some(PartialAction::Space), [
 					("w".try_into().unwrap(), Action::Save),
diff --git a/src/main.rs b/src/main.rs
index 3abd807..0403add 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,6 +1,7 @@
 #![warn(clippy::pedantic, clippy::nursery)]
 #![allow(clippy::cast_possible_truncation)]
 #![feature(get_disjoint_mut_helpers)]
+#![feature(exact_bitshifts)]
 
 use app::App;
 
@@ -20,7 +21,6 @@ const BYTES_PER_CHUNK: usize = 4;
 const CHUNKS_PER_LINE: usize = BYTES_PER_LINE / BYTES_PER_CHUNK;
 
 // TODO:
-// - J jump to offset under cursor
 // - m mark offset
 // - search
 // - s/A-k/A-K
@@ -40,6 +40,8 @@ const CHUNKS_PER_LINE: usize = BYTES_PER_LINE / BYTES_PER_CHUNK;
 // - y/p
 // - [/] to cycle view offset?
 // - gj jump to entered offset
+// - repeat X times (dec and hex)
+// - jump relative to last marker?
 
 // future directions
 // - 'views' for bytes (i8/16/etc u8/16/etc 20.12/8.4/etc)