From d392aecb792583f4f0ed85c56891aca21f76dd4c Mon Sep 17 00:00:00 2001
From: "Christopher H. Jordan" <christopherjordan87@gmail.com>
Date: Tue, 9 Aug 2022 10:49:08 +0800
Subject: [PATCH] Speed up conversion array generation.

This makes the function about 25% faster and removes a clone.
---
 src/convert/mod.rs            | 20 ++++++++++----------
 src/correlator_context/mod.rs |  2 +-
 2 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/src/convert/mod.rs b/src/convert/mod.rs
index 73c7fbf..a7d00fa 100644
--- a/src/convert/mod.rs
+++ b/src/convert/mod.rs
@@ -226,22 +226,22 @@ fn generate_full_matrix(mwax_order: Vec<usize>) -> Vec<i32> {
 ///LegacyConversionBaseline`s which tell us, for a specific output baseline, where in the input HDU
 /// to get data from (and whether it needs to be conjugated).
 ///
-pub(crate) fn generate_conversion_array(
-    rf_inputs: &mut [Rfinput],
-) -> Vec<LegacyConversionBaseline> {
-    // Sort the rf_inputs by "Input / metafits" order
-    rf_inputs.sort_by(|a, b| a.input.cmp(&b.input));
-
+pub(crate) fn generate_conversion_array(rf_inputs: &[Rfinput]) -> Vec<LegacyConversionBaseline> {
     // Ensure we have a 256 element array of rf_inputs
     // This is an OK assumption since we only use this for Legacy and OldLegacy MWA data which always must have 128 tiles
     // which is 256 rf inputs.
     assert_eq!(rf_inputs.len(), 256);
 
     // Create a vector which contains all the mwax_orders, sorted by "input" from the metafits
-    let mut mwax_order: Vec<usize> = vec![0; 256];
-    for index in 0..256 {
-        mwax_order[index] = rf_inputs[index].subfile_order as usize;
-    }
+    let mut map = rf_inputs
+        .iter()
+        .map(|rf| (rf.input, rf.subfile_order))
+        .collect::<Vec<_>>();
+    map.sort_unstable();
+    let mwax_order = map
+        .into_iter()
+        .map(|(_, subfile_order)| subfile_order as usize)
+        .collect();
 
     // Generate the full matrix
     let full_matrix: Vec<i32> = generate_full_matrix(mwax_order);
diff --git a/src/correlator_context/mod.rs b/src/correlator_context/mod.rs
index c2c7278..63dcba9 100644
--- a/src/correlator_context/mod.rs
+++ b/src/correlator_context/mod.rs
@@ -334,7 +334,7 @@ impl CorrelatorContext {
         // or just leave it empty if we're in any other format
         let legacy_conversion_table: Vec<LegacyConversionBaseline> = match gpubox_info.mwa_version {
             MWAVersion::CorrOldLegacy | MWAVersion::CorrLegacy => {
-                convert::generate_conversion_array(&mut metafits_context.rf_inputs.clone())
+                convert::generate_conversion_array(&metafits_context.rf_inputs)
             }
             _ => Vec::new(),
         };