From 43db25440ca40cd9752d8465c8cb1fed6e8ebc4e Mon Sep 17 00:00:00 2001
From: benibus <bpharks@gmx.com>
Date: Mon, 11 Sep 2023 18:04:11 -0400
Subject: [PATCH] Additions to `arrow.float16` pkg

---
 go/arrow/float16/float16.go      | 29 +++++++++++++++++++++++
 go/arrow/float16/float16_test.go | 40 ++++++++++++++++++++++++++++++++
 2 files changed, 69 insertions(+)

diff --git a/go/arrow/float16/float16.go b/go/arrow/float16/float16.go
index 4e03d13df0cae..184cf9d153287 100644
--- a/go/arrow/float16/float16.go
+++ b/go/arrow/float16/float16.go
@@ -17,6 +17,7 @@
 package float16
 
 import (
+	"encoding/binary"
 	"math"
 	"strconv"
 )
@@ -29,6 +30,11 @@ type Num struct {
 	bits uint16
 }
 
+var (
+	MaxNum = Num{bits: 0b0111101111111111}
+	MinNum = MaxNum.Negate()
+)
+
 // New creates a new half-precision floating point value from the provided
 // float32 value.
 func New(f float32) Num {
@@ -86,6 +92,11 @@ func (n Num) Div(rhs Num) Num {
 	return New(n.Float32() / rhs.Float32())
 }
 
+// Equal returns true if the value represented by n is == other
+func (n Num) Equal(other Num) bool {
+	return n.Float32() == other.Float32()
+}
+
 // Greater returns true if the value represented by n is > other
 func (n Num) Greater(other Num) bool {
 	return n.Float32() > other.Float32()
@@ -161,5 +172,23 @@ func (n Num) Sign() int {
 	return -1
 }
 
+func (n Num) Signbit() bool { return (n.bits & 0x8000) != 0 }
+
+func (n Num) IsNaN() bool { return (n.bits & 0x7fff) > 0x7c00 }
+
 func (f Num) Uint16() uint16 { return f.bits }
 func (f Num) String() string { return strconv.FormatFloat(float64(f.Float32()), 'g', -1, 32) }
+
+func FromLEBytes(src []byte) Num {
+	return Num{bits: binary.LittleEndian.Uint16(src)}
+}
+
+func (f Num) PutLEBytes(dst []byte) {
+	binary.LittleEndian.PutUint16(dst, f.bits)
+}
+
+func (f Num) ToLEBytes() []byte {
+	dst := make([]byte, 2)
+	f.PutLEBytes(dst)
+	return dst
+}
diff --git a/go/arrow/float16/float16_test.go b/go/arrow/float16/float16_test.go
index 55c3ea8b30404..c1d1f4f2e3c50 100644
--- a/go/arrow/float16/float16_test.go
+++ b/go/arrow/float16/float16_test.go
@@ -248,3 +248,43 @@ func TestSign(t *testing.T) {
 		})
 	}
 }
+
+func TestSignbit(t *testing.T) {
+	for _, tc := range []struct {
+		n    Num
+		want bool
+	}{
+		{Num{bits: 0x4580}, false}, // 5.5
+		{Num{bits: 0x0000}, false}, // 0
+		{Num{bits: 0x8000}, true},  // -0
+		{Num{bits: 0xC580}, true},  // -5.5
+	} {
+		t.Run("signbit", func(t *testing.T) {
+			n := tc.n.Signbit()
+			if got, want := n, tc.want; got != want {
+				t.Fatalf("invalid value. got=%v, want=%v", got, want)
+			}
+		})
+	}
+}
+
+func TestIsNaN(t *testing.T) {
+	for _, tc := range []struct {
+		n    Num
+		want bool
+	}{
+		{Num{bits: 0x7c00}, false}, // inf
+		{Num{bits: 0xfc00}, false}, // -inf
+		{Num{bits: 0x7c01}, true},  // nan
+		{Num{bits: 0xfc01}, true},  // -nan
+		{Num{bits: 0x7e00}, true},  // nan
+		{Num{bits: 0xfe00}, true},  // -nan
+	} {
+		t.Run("isnan", func(t *testing.T) {
+			n := tc.n.IsNaN()
+			if got, want := n, tc.want; got != want {
+				t.Fatalf("invalid value. got=%v, want=%v", got, want)
+			}
+		})
+	}
+}