From a29019de9d6dc5a3fdefe67f29a36d9ecf5a943f Mon Sep 17 00:00:00 2001
From: Jack Christensen <jack@jackchristensen.com>
Date: Sat, 30 Oct 2021 10:17:58 -0500
Subject: [PATCH] Fix binary decoding of very large numerics.

fixes #133
---
 numeric.go      | 6 +++---
 numeric_test.go | 7 +++++++
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/numeric.go b/numeric.go
index a7efa704..f5260548 100644
--- a/numeric.go
+++ b/numeric.go
@@ -452,11 +452,11 @@ func (dst *Numeric) DecodeBinary(ci *ConnInfo, src []byte) error {
 	}
 
 	rp := 0
-	ndigits := int16(binary.BigEndian.Uint16(src[rp:]))
+	ndigits := binary.BigEndian.Uint16(src[rp:])
 	rp += 2
 	weight := int16(binary.BigEndian.Uint16(src[rp:]))
 	rp += 2
-	sign := uint16(binary.BigEndian.Uint16(src[rp:]))
+	sign := binary.BigEndian.Uint16(src[rp:])
 	rp += 2
 	dscale := int16(binary.BigEndian.Uint16(src[rp:]))
 	rp += 2
@@ -504,7 +504,7 @@ func (dst *Numeric) DecodeBinary(ci *ConnInfo, src []byte) error {
 	exp := (int32(weight) - int32(ndigits) + 1) * 4
 
 	if dscale > 0 {
-		fracNBaseDigits := ndigits - weight - 1
+		fracNBaseDigits := int16(int32(ndigits) - int32(weight) - 1)
 		fracDecimalDigits := fracNBaseDigits * 4
 
 		if dscale > fracDecimalDigits {
diff --git a/numeric_test.go b/numeric_test.go
index 81595cb3..fff5a2e0 100644
--- a/numeric_test.go
+++ b/numeric_test.go
@@ -117,6 +117,10 @@ func TestNumericNormalize(t *testing.T) {
 }
 
 func TestNumericTranscode(t *testing.T) {
+	max := new(big.Int).Exp(big.NewInt(10), big.NewInt(147454), nil)
+	max.Add(max, big.NewInt(1))
+	longestNumeric := &pgtype.Numeric{Int: max, Exp: -16383, Status: pgtype.Present}
+
 	testutil.TestSuccessfulTranscodeEqFunc(t, "numeric", []interface{}{
 		&pgtype.Numeric{NaN: true, Status: pgtype.Present},
 
@@ -151,6 +155,9 @@ func TestNumericTranscode(t *testing.T) {
 		&pgtype.Numeric{Int: mustParseBigInt(t, "423409823409243892349028349023482934092340892390101"), Exp: -92, Status: pgtype.Present},
 		&pgtype.Numeric{Int: mustParseBigInt(t, "23409823409243892349028349023482934092340892390101"), Exp: -93, Status: pgtype.Present},
 		&pgtype.Numeric{Int: mustParseBigInt(t, "3409823409243892349028349023482934092340892390101"), Exp: -94, Status: pgtype.Present},
+
+		longestNumeric,
+
 		&pgtype.Numeric{Status: pgtype.Null},
 	}, func(aa, bb interface{}) bool {
 		a := aa.(pgtype.Numeric)