From d09aa9f873789f73a8dc1f046a09643a5e5b317a Mon Sep 17 00:00:00 2001
From: Andrew Kane <andrew@ankane.org>
Date: Mon, 4 Dec 2023 12:49:28 -0800
Subject: [PATCH] Added casts between half to double precision [skip ci]

---
 sql/vector--0.5.1--0.6.0.sql | 12 ++++++++++++
 sql/vector.sql               | 12 ++++++++++++
 src/half.c                   | 36 ++++++++++++++++++++++++++++++++++++
 test/expected/half.out       | 12 ++++++++++++
 test/sql/half.sql            |  3 +++
 5 files changed, 75 insertions(+)

diff --git a/sql/vector--0.5.1--0.6.0.sql b/sql/vector--0.5.1--0.6.0.sql
index 3b9115e..2865352 100644
--- a/sql/vector--0.5.1--0.6.0.sql
+++ b/sql/vector--0.5.1--0.6.0.sql
@@ -49,6 +49,12 @@ CREATE FUNCTION float4_to_half(real, integer, boolean) RETURNS half
 CREATE FUNCTION half_to_float4(half, integer, boolean) RETURNS real
 	AS 'MODULE_PATHNAME' LANGUAGE C IMMUTABLE STRICT PARALLEL SAFE;
 
+CREATE FUNCTION float8_to_half(float8, integer, boolean) RETURNS half
+	AS 'MODULE_PATHNAME' LANGUAGE C IMMUTABLE STRICT PARALLEL SAFE;
+
+CREATE FUNCTION half_to_float8(half, integer, boolean) RETURNS float8
+	AS 'MODULE_PATHNAME' LANGUAGE C IMMUTABLE STRICT PARALLEL SAFE;
+
 CREATE FUNCTION integer_to_half(integer, integer, boolean) RETURNS half
 	AS 'MODULE_PATHNAME' LANGUAGE C IMMUTABLE STRICT PARALLEL SAFE;
 
@@ -64,6 +70,12 @@ CREATE CAST (real AS half)
 CREATE CAST (half AS real)
 	WITH FUNCTION half_to_float4(half, integer, boolean) AS IMPLICIT;
 
+CREATE CAST (float8 AS half)
+	WITH FUNCTION float8_to_half(float8, integer, boolean) AS IMPLICIT;
+
+CREATE CAST (half AS float8)
+	WITH FUNCTION half_to_float8(half, integer, boolean) AS IMPLICIT;
+
 CREATE CAST (integer AS half)
 	WITH FUNCTION integer_to_half(integer, integer, boolean) AS IMPLICIT;
 
diff --git a/sql/vector.sql b/sql/vector.sql
index dfa1c7c..ad1be73 100644
--- a/sql/vector.sql
+++ b/sql/vector.sql
@@ -347,6 +347,12 @@ CREATE FUNCTION float4_to_half(real, integer, boolean) RETURNS half
 CREATE FUNCTION half_to_float4(half, integer, boolean) RETURNS real
 	AS 'MODULE_PATHNAME' LANGUAGE C IMMUTABLE STRICT PARALLEL SAFE;
 
+CREATE FUNCTION float8_to_half(float8, integer, boolean) RETURNS half
+	AS 'MODULE_PATHNAME' LANGUAGE C IMMUTABLE STRICT PARALLEL SAFE;
+
+CREATE FUNCTION half_to_float8(half, integer, boolean) RETURNS float8
+	AS 'MODULE_PATHNAME' LANGUAGE C IMMUTABLE STRICT PARALLEL SAFE;
+
 CREATE FUNCTION integer_to_half(integer, integer, boolean) RETURNS half
 	AS 'MODULE_PATHNAME' LANGUAGE C IMMUTABLE STRICT PARALLEL SAFE;
 
@@ -364,6 +370,12 @@ CREATE CAST (real AS half)
 CREATE CAST (half AS real)
 	WITH FUNCTION half_to_float4(half, integer, boolean) AS IMPLICIT;
 
+CREATE CAST (float8 AS half)
+	WITH FUNCTION float8_to_half(float8, integer, boolean) AS IMPLICIT;
+
+CREATE CAST (half AS float8)
+	WITH FUNCTION half_to_float8(half, integer, boolean) AS IMPLICIT;
+
 CREATE CAST (integer AS half)
 	WITH FUNCTION integer_to_half(integer, integer, boolean) AS IMPLICIT;
 
diff --git a/src/half.c b/src/half.c
index 5199eff..bcbde77 100644
--- a/src/half.c
+++ b/src/half.c
@@ -298,6 +298,16 @@ Float4ToHalf(float num)
 	return result;
 }
 
+/*
+ * Convert a float8 to a half
+ */
+static half
+Float8ToHalf(double num)
+{
+	/* TODO Convert directly for greater accuracy */
+	return Float4ToHalf((float) num);
+}
+
 /*
  * Convert textual representation to internal representation
  */
@@ -466,6 +476,32 @@ half_to_float4(PG_FUNCTION_ARGS)
 	PG_RETURN_FLOAT4(f);
 }
 
+/*
+ * Convert float8 to half
+ */
+PGDLLEXPORT PG_FUNCTION_INFO_V1(float8_to_half);
+Datum
+float8_to_half(PG_FUNCTION_ARGS)
+{
+	float8		d = PG_GETARG_FLOAT8(0);
+	half		h = Float8ToHalf(d);
+
+	PG_RETURN_HALF(h);
+}
+
+/*
+ * Convert half to float8
+ */
+PGDLLEXPORT PG_FUNCTION_INFO_V1(half_to_float8);
+Datum
+half_to_float8(PG_FUNCTION_ARGS)
+{
+	half		h = PG_GETARG_HALF(0);
+	float		f = HalfToFloat4(h);
+
+	PG_RETURN_FLOAT8((double) f);
+}
+
 /*
  * Get the L2 distance between half arrays
  */
diff --git a/test/expected/half.out b/test/expected/half.out
index 95f4439..7188963 100644
--- a/test/expected/half.out
+++ b/test/expected/half.out
@@ -94,6 +94,18 @@ SELECT '1.5'::real::half;
  1.5
 (1 row)
 
+SELECT '1.5'::half::double precision;
+ float8 
+--------
+    1.5
+(1 row)
+
+SELECT '1.5'::double precision::half;
+ half 
+------
+ 1.5
+(1 row)
+
 SELECT '1.5'::half::numeric;
  numeric 
 ---------
diff --git a/test/sql/half.sql b/test/sql/half.sql
index 7b01e1c..6588322 100644
--- a/test/sql/half.sql
+++ b/test/sql/half.sql
@@ -21,6 +21,9 @@ SELECT 'Infinity'::real::half;
 SELECT '1.5'::half::real;
 SELECT '1.5'::real::half;
 
+SELECT '1.5'::half::double precision;
+SELECT '1.5'::double precision::half;
+
 SELECT '1.5'::half::numeric;
 SELECT '1.5'::numeric::half;