From 9e8413586b23fa53575941448dc0f019bb870294 Mon Sep 17 00:00:00 2001
From: Michael Erickson <michae2@cockroachlabs.com>
Date: Fri, 16 Aug 2024 14:44:27 -0700
Subject: [PATCH] eval: fix hlc_to_timestamp builtin

Builtin function `hlc_to_timestamp` calls internal function
`decimalToHLC` which was assuming all input decimals had -10 as the
exponent. But some decimals may have other exponents. It's more robust
to call `Int64()` on the floored decimal, which handles any exponent.

Fixes: #129152

Release note (bug fix): Fix a bug that would cause `hlc_to_timestamp` to
return an incorrect timestamp for some input decimals.
---
 pkg/sql/sem/eval/context.go             | 15 ++++++++-------
 pkg/sql/sem/eval/testdata/eval/builtins | 10 ++++++++++
 2 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/pkg/sql/sem/eval/context.go b/pkg/sql/sem/eval/context.go
index 72f4e6f71aec..c914d52952a4 100644
--- a/pkg/sql/sem/eval/context.go
+++ b/pkg/sql/sem/eval/context.go
@@ -672,18 +672,19 @@ func DecimalToInexactDTimestampTZ(d *tree.DDecimal) (*tree.DTimestampTZ, error)
 }
 
 func decimalToHLC(d *tree.DDecimal) (hlc.Timestamp, error) {
-	var coef apd.BigInt
-	coef.Set(&d.Decimal.Coeff)
-	// The physical portion of the HLC is stored shifted up by 10^10, so shift
-	// it down and clear out the logical component.
-	coef.Div(&coef, big10E10)
-	if !coef.IsInt64() {
+	var floorD apd.Decimal
+	if _, err := tree.DecimalCtx.Floor(&floorD, &d.Decimal); err != nil {
+		return hlc.Timestamp{}, err
+	}
+
+	i, err := floorD.Int64()
+	if err != nil {
 		return hlc.Timestamp{}, pgerror.Newf(
 			pgcode.DatetimeFieldOverflow,
 			"timestamp value out of range: %s", d.String(),
 		)
 	}
-	return hlc.Timestamp{WallTime: coef.Int64()}, nil
+	return hlc.Timestamp{WallTime: i}, nil
 }
 
 // DecimalToInexactDTimestamp is the inverse of TimestampToDecimal. It converts
diff --git a/pkg/sql/sem/eval/testdata/eval/builtins b/pkg/sql/sem/eval/testdata/eval/builtins
index 1b12094db558..2987cb806731 100644
--- a/pkg/sql/sem/eval/testdata/eval/builtins
+++ b/pkg/sql/sem/eval/testdata/eval/builtins
@@ -172,3 +172,13 @@ eval
 hlc_to_timestamp(1627966319623050000.0000000000)
 ----
 '2021-08-03 04:51:59.62305+00'
+
+eval
+hlc_to_timestamp(1627966319623050000)
+----
+'2021-08-03 04:51:59.62305+00'
+
+eval
+hlc_to_timestamp(1627966319623050000.00)
+----
+'2021-08-03 04:51:59.62305+00'