From 85967d6dbb5d0d8afb0a09ed25abbe9d067c12b7 Mon Sep 17 00:00:00 2001
From: bensynapse <118375461+bensynapse@users.noreply.github.com>
Date: Thu, 17 Sep 2026 20:07:25 +0300
Subject: [PATCH] Preserve FIT records on the equator and prime meridian

---
 core/src/lib.rs                | 12 ++++--
 core/tests/fit_parser_tests.rs | 68 ++++++++++++++++++++++++++++++++++
 2 files changed, 76 insertions(+), 4 deletions(-)

diff --git a/core/src/lib.rs b/core/src/lib.rs
index 0709d7e..459364b 100644
--- a/core/src/lib.rs
+++ b/core/src/lib.rs
@@ -661,7 +661,7 @@ impl FitParser {
             self.read_u8().unwrap_or(0),
             self.read_u8().unwrap_or(0),
         ];
-        if signature != [b'.', b'F', b'I', b'T'] {
+        if signature != *b".FIT" {
             return coordinates;
         }
 
@@ -890,7 +890,7 @@ impl FitParser {
                     // Latitude field
                     if field.size == 4 {
                         if let Some(lat_raw) = self.read_i32_le() {
-                            if lat_raw != 0x7FFFFFFF && lat_raw != 0 {
+                            if lat_raw != 0x7FFFFFFF {
                                 let lat_degrees = lat_raw as f64 * (180.0 / 2147483648.0);
                                 if lat_degrees.abs() <= 90.0 {
                                     lat = Some(lat_degrees);
@@ -905,7 +905,7 @@ impl FitParser {
                     // Longitude field
                     if field.size == 4 {
                         if let Some(lon_raw) = self.read_i32_le() {
-                            if lon_raw != 0x7FFFFFFF && lon_raw != 0 {
+                            if lon_raw != 0x7FFFFFFF {
                                 let lon_degrees = lon_raw as f64 * (180.0 / 2147483648.0);
                                 if lon_degrees.abs() <= 180.0 {
                                     lon = Some(lon_degrees);
@@ -924,7 +924,11 @@ impl FitParser {
         }
 
         if let (Some(lat_val), Some(lon_val)) = (lat, lon) {
-            Some([round(lat_val), round(lon_val)])
+            if is_valid_coordinate(lat_val, lon_val) {
+                Some([round(lat_val), round(lon_val)])
+            } else {
+                None
+            }
         } else {
             None
         }
diff --git a/core/tests/fit_parser_tests.rs b/core/tests/fit_parser_tests.rs
index 008ce1e..3d03b40 100644
--- a/core/tests/fit_parser_tests.rs
+++ b/core/tests/fit_parser_tests.rs
@@ -253,6 +253,74 @@ mod fit_parser_tests {
         assert!(result.is_none());
     }
 
+    #[test]
+    fn test_parse_record_message_equator() {
+        let definition = create_test_message_definition(20);
+        for longitude in [-45.0, 45.0] {
+            let mut data = Vec::new();
+            data.extend_from_slice(&0i32.to_le_bytes());
+            data.extend_from_slice(&((longitude * 2147483648.0 / 180.0) as i32).to_le_bytes());
+            data.extend_from_slice(&1234u16.to_le_bytes());
+
+            let mut parser = create_test_parser(data);
+            assert_eq!(
+                parser.parse_record_message(&definition),
+                Some([0.0, longitude])
+            );
+            assert_eq!(parser.pos, parser.data.len());
+        }
+    }
+
+    #[test]
+    fn test_parse_record_message_prime_meridian() {
+        let definition = create_test_message_definition(20);
+        for latitude in [-45.0, 45.0] {
+            let mut data = Vec::new();
+            data.extend_from_slice(&((latitude * 2147483648.0 / 180.0) as i32).to_le_bytes());
+            data.extend_from_slice(&0i32.to_le_bytes());
+            data.extend_from_slice(&1234u16.to_le_bytes());
+
+            let mut parser = create_test_parser(data);
+            assert_eq!(
+                parser.parse_record_message(&definition),
+                Some([latitude, 0.0])
+            );
+            assert_eq!(parser.pos, parser.data.len());
+        }
+    }
+
+    #[test]
+    fn test_parse_gps_coordinates_zero_axes() {
+        // A local record definition with signed latitude and longitude fields.
+        let mut records = vec![0x40, 0, 0, 20, 0, 2, 0, 4, 0x85, 1, 4, 0x85];
+        let quarter_circle = 1i32 << 29; // 45 degrees in semicircles
+        for (lat, lon) in [
+            (0, quarter_circle),
+            (0, -quarter_circle),
+            (quarter_circle, 0),
+            (-quarter_circle, 0),
+            (i32::MAX, quarter_circle),
+            (quarter_circle, i32::MAX),
+            (0, 0),
+        ] {
+            records.push(0); // Local record message header
+            records.extend_from_slice(&lat.to_le_bytes());
+            records.extend_from_slice(&lon.to_le_bytes());
+        }
+
+        let mut data = vec![12, 0x10, 0, 0];
+        data.extend_from_slice(&(records.len() as u32).to_le_bytes());
+        data.extend_from_slice(b".FIT");
+        data.extend_from_slice(&records);
+        data.extend_from_slice(&[0, 0]); // CRC is not checked by this parser
+
+        let mut parser = create_test_parser(data);
+        assert_eq!(
+            parser.parse_gps_coordinates(),
+            vec![[0.0, 45.0], [0.0, -45.0], [45.0, 0.0], [-45.0, 0.0]]
+        );
+    }
+
     #[test]
     fn test_parse_record_message_out_of_range_coordinates() {
         let definition = create_test_message_definition(20);