chore: import upstream snapshot with attribution

server/functions/log.go

@@ -0,0 +1,134 @@
+// Copyright 2024 Dolthub, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package functions
+
+import (
+	"math"
+	"strings"
+
+	"github.com/cockroachdb/apd/v3"
+	"github.com/cockroachdb/errors"
+	"github.com/dolthub/go-mysql-server/sql"
+
+	"github.com/dolthub/doltgresql/server/functions/framework"
+	pgtypes "github.com/dolthub/doltgresql/server/types"
+)
+
+// initLog registers the functions to the catalog.
+func initLog() {
+	framework.RegisterFunction(log_float64)
+	framework.RegisterFunction(log_numeric)
+	framework.RegisterFunction(log_numeric_numeric)
+}
+
+// log_float64 represents the PostgreSQL function of the same name, taking the same parameters.
+var log_float64 = framework.Function1{
+	Name:       "log",
+	Return:     pgtypes.Float64,
+	Parameters: [1]*pgtypes.DoltgresType{pgtypes.Float64},
+	Strict:     true,
+	Callable: func(ctx *sql.Context, _ [2]*pgtypes.DoltgresType, val1Interface any) (any, error) {
+		val1 := val1Interface.(float64)
+		if val1 == 0 {
+			return nil, errors.Errorf("cannot take logarithm of zero")
+		} else if val1 < 0 {
+			return nil, errors.Errorf("cannot take logarithm of a negative number")
+		}
+		return math.Log10(val1), nil
+	},
+}
+
+// log_numeric represents the PostgreSQL function of the same name, taking the same parameters.
+var log_numeric = framework.Function1{
+	Name:       "log",
+	Return:     pgtypes.Numeric,
+	Parameters: [1]*pgtypes.DoltgresType{pgtypes.Numeric},
+	Strict:     true,
+	Callable: func(ctx *sql.Context, _ [2]*pgtypes.DoltgresType, val1 any) (any, error) {
+		dec := val1.(*apd.Decimal)
+		if dec.IsZero() {
+			return nil, errors.Errorf("cannot take logarithm of zero")
+		} else if dec.Sign() < 0 {
+			return nil, errors.Errorf("cannot take logarithm of a negative number")
+		}
+
+		// calculate precision and scale
+		p := uint32(17)
+		if dec.Exponent < 0 {
+			p += uint32(-dec.Exponent)
+		}
+
+		res := new(apd.Decimal)
+		_, err := sql.DecimalCtx.WithPrecision(p).Log10(res, dec)
+		if err != nil {
+			return nil, err
+		}
+		return res, nil
+	},
+}
+
+// log_numeric_numeric represents the PostgreSQL function of the same name, taking the same parameters.
+var log_numeric_numeric = framework.Function2{
+	Name:       "log",
+	Return:     pgtypes.Numeric,
+	Parameters: [2]*pgtypes.DoltgresType{pgtypes.Numeric, pgtypes.Numeric},
+	Strict:     true,
+	Callable: func(ctx *sql.Context, _ [3]*pgtypes.DoltgresType, val1 any, val2 any) (any, error) {
+		base := val1.(*apd.Decimal)
+		num := val2.(*apd.Decimal)
+		if base.IsZero() || num.IsZero() {
+			return nil, errors.Errorf("cannot take logarithm of zero")
+		} else if base.Sign() < 0 || num.Sign() < 0 {
+			return nil, errors.Errorf("cannot take logarithm of a negative number")
+		}
+
+		// TODO: calculate precision and scale accurately
+		sNum := num.Text('f')
+		sBase := base.Text('f')
+		partsNum := strings.Split(sNum, ".")
+		partsBase := strings.Split(sBase, ".")
+		exp := int32(-16)
+		if minExp := math.Min(float64(base.Exponent), float64(num.Exponent)); int32(minExp) < exp {
+			exp = int32(minExp)
+		}
+		p := uint32(int32(math.Max(float64(len(partsNum[0])), float64(len(partsBase[0])))) + (-exp))
+		c := sql.DecimalCtx.WithPrecision(p)
+
+		lnBase := new(apd.Decimal)
+		_, err := c.Ln(lnBase, base)
+		if err != nil {
+			return nil, err
+		}
+		if lnBase.IsZero() {
+			return nil, errors.Errorf("division by zero")
+		}
+
+		lnNum := new(apd.Decimal)
+		_, err = c.Ln(lnNum, num)
+		if err != nil {
+			return nil, err
+		}
+		if lnNum.IsZero() {
+			return apd.New(0, -16), nil
+		}
+
+		res := new(apd.Decimal)
+		_, err = c.Quo(res, lnNum, lnBase)
+		if err != nil {
+			return nil, err
+		}
+		return sql.DecimalRound(res, -exp)
+	},
+}