feat: dequantize (#431)

closes #427

Signed-off-by: usamoi <usamoi@outlook.com>

Author: usamoi

src/datatype/functions_rabitq4.rs

@@ -12,12 +12,13 @@
 //
 // Copyright (c) 2025 TensorChord Inc.
 
-use crate::datatype::memory_halfvec::HalfvecInput;
-use crate::datatype::memory_rabitq4::Rabitq4Output;
-use crate::datatype::memory_vector::VectorInput;
+use crate::datatype::memory_halfvec::{HalfvecInput, HalfvecOutput};
+use crate::datatype::memory_rabitq4::{Rabitq4Input, Rabitq4Output};
+use crate::datatype::memory_vector::{VectorInput, VectorOutput};
 use simd::{Floating, f16};
 use vector::VectorBorrowed;
 use vector::rabitq4::Rabitq4Borrowed;
+use vector::vect::VectBorrowed;
 
 #[pgrx::pg_extern(sql = "")]
 fn _vchord_vector_quantize_to_rabitq4(vector: VectorInput) -> Rabitq4Output {
@@ -54,3 +55,30 @@ fn _vchord_halfvec_quantize_to_rabitq4(vector: HalfvecInput) -> Rabitq4Output {
         &elements,
     ))
 }
+
+#[pgrx::pg_extern(sql = "")]
+fn _vchord_rabitq4_dequantize_to_vector(vector: Rabitq4Input) -> VectorOutput {
+    let vector = vector.as_borrowed();
+    let scale = vector.sum_of_x2().sqrt() / vector.norm_of_lattice();
+    let mut result = Vec::with_capacity(vector.dim() as _);
+    for c in vector.unpacked_code() {
+        let base = -0.5 * ((1 << 4) - 1) as f32;
+        result.push((base + c as f32) * scale);
+    }
+    rabitq::rotate::rotate_reversed_inplace(&mut result);
+    VectorOutput::new(VectBorrowed::new(&result))
+}
+
+#[pgrx::pg_extern(sql = "")]
+fn _vchord_rabitq4_dequantize_to_halfvec(vector: Rabitq4Input) -> HalfvecOutput {
+    let vector = vector.as_borrowed();
+    let scale = vector.sum_of_x2().sqrt() / vector.norm_of_lattice();
+    let mut result = Vec::with_capacity(vector.dim() as _);
+    for c in vector.unpacked_code() {
+        let base = -0.5 * ((1 << 4) - 1) as f32;
+        result.push((base + c as f32) * scale);
+    }
+    rabitq::rotate::rotate_reversed_inplace(&mut result);
+    let result = f16::vector_from_f32(&result);
+    HalfvecOutput::new(VectBorrowed::new(&result))
+}

src/datatype/functions_rabitq8.rs

@@ -12,12 +12,13 @@
 //
 // Copyright (c) 2025 TensorChord Inc.
 
-use crate::datatype::memory_halfvec::HalfvecInput;
-use crate::datatype::memory_rabitq8::Rabitq8Output;
-use crate::datatype::memory_vector::VectorInput;
+use crate::datatype::memory_halfvec::{HalfvecInput, HalfvecOutput};
+use crate::datatype::memory_rabitq8::{Rabitq8Input, Rabitq8Output};
+use crate::datatype::memory_vector::{VectorInput, VectorOutput};
 use simd::{Floating, f16};
 use vector::VectorBorrowed;
 use vector::rabitq8::Rabitq8Borrowed;
+use vector::vect::VectBorrowed;
 
 #[pgrx::pg_extern(sql = "")]
 fn _vchord_vector_quantize_to_rabitq8(vector: VectorInput) -> Rabitq8Output {
@@ -54,3 +55,30 @@ fn _vchord_halfvec_quantize_to_rabitq8(vector: HalfvecInput) -> Rabitq8Output {
         &elements,
     ))
 }
+
+#[pgrx::pg_extern(sql = "")]
+fn _vchord_rabitq8_dequantize_to_vector(vector: Rabitq8Input) -> VectorOutput {
+    let vector = vector.as_borrowed();
+    let scale = vector.sum_of_x2().sqrt() / vector.norm_of_lattice();
+    let mut result = Vec::with_capacity(vector.dim() as _);
+    for c in vector.unpacked_code() {
+        let base = -0.5 * ((1 << 8) - 1) as f32;
+        result.push((base + c as f32) * scale);
+    }
+    rabitq::rotate::rotate_reversed_inplace(&mut result);
+    VectorOutput::new(VectBorrowed::new(&result))
+}
+
+#[pgrx::pg_extern(sql = "")]
+fn _vchord_rabitq8_dequantize_to_halfvec(vector: Rabitq8Input) -> HalfvecOutput {
+    let vector = vector.as_borrowed();
+    let scale = vector.sum_of_x2().sqrt() / vector.norm_of_lattice();
+    let mut result = Vec::with_capacity(vector.dim() as _);
+    for c in vector.unpacked_code() {
+        let base = -0.5 * ((1 << 8) - 1) as f32;
+        result.push((base + c as f32) * scale);
+    }
+    rabitq::rotate::rotate_reversed_inplace(&mut result);
+    let result = f16::vector_from_f32(&result);
+    HalfvecOutput::new(VectBorrowed::new(&result))
+}

src/datatype/memory_halfvec.rs

@@ -102,7 +102,6 @@ impl HalfvecOutput {
         }
         Self(q)
     }
-    #[expect(dead_code)]
     pub fn new(vector: VectBorrowed<'_, f16>) -> Self {
         unsafe {
             let slice = vector.slice();

src/datatype/memory_vector.rs

@@ -101,7 +101,6 @@ impl VectorOutput {
         }
         Self(q)
     }
-    #[expect(dead_code)]
     pub fn new(vector: VectBorrowed<'_, f32>) -> Self {
         unsafe {
             let slice = vector.slice();

src/sql/finalize.sql

@@ -206,12 +206,24 @@ IMMUTABLE STRICT PARALLEL SAFE LANGUAGE c AS 'MODULE_PATHNAME', '_vchord_vector_
 CREATE FUNCTION quantize_to_rabitq8(halfvec) RETURNS rabitq8
 IMMUTABLE STRICT PARALLEL SAFE LANGUAGE c AS 'MODULE_PATHNAME', '_vchord_halfvec_quantize_to_rabitq8_wrapper';
 
+CREATE FUNCTION dequantize_to_vector(rabitq8) RETURNS vector
+IMMUTABLE STRICT PARALLEL SAFE LANGUAGE c AS 'MODULE_PATHNAME', '_vchord_rabitq8_dequantize_to_vector_wrapper';
+
+CREATE FUNCTION dequantize_to_halfvec(rabitq8) RETURNS halfvec
+IMMUTABLE STRICT PARALLEL SAFE LANGUAGE c AS 'MODULE_PATHNAME', '_vchord_rabitq8_dequantize_to_halfvec_wrapper';
+
 CREATE FUNCTION quantize_to_rabitq4(vector) RETURNS rabitq4
 IMMUTABLE STRICT PARALLEL SAFE LANGUAGE c AS 'MODULE_PATHNAME', '_vchord_vector_quantize_to_rabitq4_wrapper';
 
 CREATE FUNCTION quantize_to_rabitq4(halfvec) RETURNS rabitq4
 IMMUTABLE STRICT PARALLEL SAFE LANGUAGE c AS 'MODULE_PATHNAME', '_vchord_halfvec_quantize_to_rabitq4_wrapper';
 
+CREATE FUNCTION dequantize_to_vector(rabitq4) RETURNS vector
+IMMUTABLE STRICT PARALLEL SAFE LANGUAGE c AS 'MODULE_PATHNAME', '_vchord_rabitq4_dequantize_to_vector_wrapper';
+
+CREATE FUNCTION dequantize_to_halfvec(rabitq4) RETURNS halfvec
+IMMUTABLE STRICT PARALLEL SAFE LANGUAGE c AS 'MODULE_PATHNAME', '_vchord_rabitq4_dequantize_to_halfvec_wrapper';
+
 CREATE FUNCTION vchordrq_sampled_values(regclass) RETURNS SETOF TEXT
 STRICT LANGUAGE c AS 'MODULE_PATHNAME', '_vchordrq_sampled_values_wrapper';
 

tests/general/dequantize.slt

@@ -0,0 +1,19 @@
+query I
+SELECT dequantize_to_vector(quantize_to_rabitq8('[1,2,3,4,5,6,7,8]'::vector)) <-> '[1,2,3,4,5,6,7,8]'::vector < 0.07;
+----
+t
+
+query I
+SELECT dequantize_to_halfvec(quantize_to_rabitq8('[1,2,3,4,5,6,7,8]'::halfvec)) <-> '[1,2,3,4,5,6,7,8]'::halfvec < 0.07;
+----
+t
+
+query I
+SELECT dequantize_to_vector(quantize_to_rabitq4('[1,2,3,4,5,6,7,8]'::vector)) <-> '[1,2,3,4,5,6,7,8]'::vector < 1.00;
+----
+t
+
+query I
+SELECT dequantize_to_halfvec(quantize_to_rabitq4('[1,2,3,4,5,6,7,8]'::halfvec)) <-> '[1,2,3,4,5,6,7,8]'::halfvec < 1.00;
+----
+t