chore: import upstream snapshot with attribution

server/functions/power.go

@@ -0,0 +1,126 @@
+// 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"
+
+	"github.com/cockroachdb/apd/v3"
+	"github.com/cockroachdb/errors"
+	"github.com/dolthub/go-mysql-server/sql"
+	"github.com/dolthub/go-mysql-server/sql/types"
+
+	"github.com/dolthub/doltgresql/server/functions/framework"
+	pgtypes "github.com/dolthub/doltgresql/server/types"
+)
+
+// initPower registers the functions to the catalog.
+func initPower() {
+	framework.RegisterFunction(power_float64_float64)
+	framework.RegisterFunction(power_numeric_numeric)
+}
+
+var (
+	// errPowerZeroToNegative is an error for raising zero to a negative power in the "power" functions.
+	errPowerZeroToNegative = errors.New("zero raised to a negative power is undefined")
+	// numericOne is equivalent to apt.NewFromInt(1, 0), but represented as a value for the sake of efficiency.
+	numericOne = apd.New(1, 0)
+)
+
+// power_float64_float64 represents the PostgreSQL function of the same name, taking the same parameters.
+var power_float64_float64 = framework.Function2{
+	Name:       "power",
+	Return:     pgtypes.Float64,
+	Parameters: [2]*pgtypes.DoltgresType{pgtypes.Float64, pgtypes.Float64},
+	Strict:     true,
+	Callable: func(ctx *sql.Context, _ [3]*pgtypes.DoltgresType, val1 any, val2 any) (any, error) {
+		f1 := val1.(float64)
+		f2 := val2.(float64)
+		if f1 == 0 && f2 < 0 {
+			return nil, errPowerZeroToNegative
+		}
+		return math.Pow(f1, f2), nil
+	},
+}
+
+// power_numeric_numeric represents the PostgreSQL function of the same name, taking the same parameters.
+var power_numeric_numeric = framework.Function2{
+	Name:       "power",
+	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) {
+		dec1 := val1.(*apd.Decimal)
+		dec2 := val2.(*apd.Decimal)
+		if dec1.Form == apd.NaN || dec2.Form == apd.NaN {
+			return pgtypes.NumericNaN, nil
+		}
+		if dec1.Form == apd.Infinite && dec1.Negative {
+			// dec1 is -Infinity
+			even := dec2.Form == apd.Infinite && !dec2.Negative
+			if dec2.Form == apd.Finite {
+				i, err := dec2.Int64()
+				if err != nil {
+					return nil, errors.Errorf(`a negative number raised to a non-integer power yields a complex result`)
+				}
+				even = i%2 == 0
+			}
+			if dec2.Sign() > 0 {
+				// +inf will return neginf == fix!!
+				if even {
+					return pgtypes.NumericInf, nil
+				}
+				return pgtypes.NumericNegInf, nil
+			}
+			if (dec2.Form == apd.Infinite && dec2.Negative) || dec2.Sign() < 0 {
+				return apd.New(0, 0), nil
+			}
+			return apd.New(1, 0), nil
+		} else if dec1.Form == apd.Infinite {
+			// dec1 is +Infinity
+			d2Sign := dec2.Sign()
+			if dec2.Sign() < 0 {
+				return apd.New(0, 0), nil
+			} else if d2Sign == 0 {
+				return apd.New(1, 0), nil
+			}
+			return types.DecimalPosInf, nil
+		} else if dec1.IsZero() {
+			// dec1 is 0
+			if dec2.Sign() < 0 {
+				// includes neg inf
+				return nil, errPowerZeroToNegative
+			}
+			if dec2.Form == apd.Infinite {
+				return apd.New(0, 0), nil
+			}
+			if dec2.Sign() > 0 {
+				return sql.DecimalRound(apd.New(0, 0), 16)
+			}
+		}
+		// decimal.Pow() does not handle the zero exponent properly, so we special case it
+		if dec2.IsZero() || dec1.Cmp(numericOne) == 0 {
+			return sql.DecimalRound(apd.New(1, 0), 16)
+		}
+
+		// give enough precision that we can round it to 16 exp
+		res := new(apd.Decimal)
+		_, err := sql.DecimalCtx.WithPrecision(17).Pow(res, dec1, dec2)
+		if err != nil {
+			return nil, err
+		}
+		return sql.DecimalRound(res, 16)
+	},
+}