From 90ece37a65996fb9c999007c4467f7c4d440e1c5 Mon Sep 17 00:00:00 2001
From: "Alex Razumov (from Dev Box)" <alrazu@microsoft.com>
Date: Mon, 5 Oct 2026 11:35:02 -0700
Subject: [PATCH] fix(disk): round-trip default scalar quantization

Align the serialized spelling for SQ's default standard deviation with the parser's canonical SQ_N form.
---
 .../build/configuration/quantization_types.rs | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/diskann-disk/src/build/configuration/quantization_types.rs b/diskann-disk/src/build/configuration/quantization_types.rs
index bafae97895..5fa691d646 100644
--- a/diskann-disk/src/build/configuration/quantization_types.rs
+++ b/diskann-disk/src/build/configuration/quantization_types.rs
@@ -211,13 +211,10 @@ impl Display for QuantizationType {
             QuantizationType::SQ {
                 nbits,
                 standard_deviation,
-            } => {
-                let standard_deviation = match standard_deviation {
-                    Some(sd) => sd.into_inner().to_string(),
-                    None => "None".to_string(),
-                };
-                write!(f, "SQ_{}_{}", nbits, standard_deviation)
-            }
+            } => match standard_deviation {
+                Some(sd) => write!(f, "SQ_{}_{}", nbits, sd.into_inner()),
+                None => write!(f, "SQ_{}", nbits),
+            },
         }
     }
 }
@@ -281,7 +278,7 @@ mod tests {
     #[case(QuantizationType::Spherical(SphericalBits::One), "SPHERICAL_1")]
     #[case(
         QuantizationType::SQ { nbits: 8, standard_deviation: None },
-        "SQ_8_None"
+        "SQ_8"
     )]
     #[case(
         QuantizationType::SQ {
@@ -331,11 +328,13 @@ mod tests {
 
     #[test]
     fn test_roundtrip_serialization() {
-        // Note: SQ with None standard_deviation is not included as it formats to "SQ_N_None"
-        // which the parser doesn't accept - this is a known limitation of the current implementation
         let types = vec![
             QuantizationType::FP,
             QuantizationType::PQ { num_chunks: 256 },
+            QuantizationType::SQ {
+                nbits: 8,
+                standard_deviation: None,
+            },
             QuantizationType::SQ {
                 nbits: 8,
                 standard_deviation: Some(Positive::new(1.5).unwrap()),