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conv.go
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conv.go
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// Copyright 2022 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 function
import (
"fmt"
"math"
"strconv"
"strings"
"github.com/gabereiser/go-mysql-server/sql"
"github.com/gabereiser/go-mysql-server/sql/types"
)
// Conv function converts numbers between different number bases. Returns a string representation of the number N, converted from base from_base to base to_base.
type Conv struct {
n sql.Expression
fromBase sql.Expression
toBase sql.Expression
}
var _ sql.FunctionExpression = (*Conv)(nil)
// NewConv returns a new Conv expression.
func NewConv(n, from, to sql.Expression) sql.Expression {
return &Conv{n, from, to}
}
// FunctionName implements sql.FunctionExpression
func (c *Conv) FunctionName() string {
return "conv"
}
// Description implements sql.FunctionExpression
func (c *Conv) Description() string {
return "returns a string representation of the number N, converted from base from_base to base to_base."
}
// Type implements the Expression interface.
func (c *Conv) Type() sql.Type { return types.LongText }
// IsNullable implements the Expression interface.
func (c *Conv) IsNullable() bool {
return c.n.IsNullable() || c.fromBase.IsNullable() || c.toBase.IsNullable()
}
func (c *Conv) String() string {
return fmt.Sprintf("%s(%s,%s,%s)", c.FunctionName(), c.n, c.fromBase, c.toBase)
}
// Eval implements the Expression interface.
func (c *Conv) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
n, err := c.n.Eval(ctx, row)
if err != nil {
return nil, err
}
if n == nil {
return nil, nil
}
from, err := c.fromBase.Eval(ctx, row)
if err != nil {
return nil, err
}
if from == nil {
return nil, nil
}
to, err := c.toBase.Eval(ctx, row)
if err != nil {
return nil, err
}
if to == nil {
return nil, nil
}
n, err = types.LongText.Convert(n)
if err != nil {
return nil, nil
}
// valConvertedFrom is unsigned if n input is positive, signed if negative.
valConvertedFrom := convertFromBase(n.(string), from)
switch valConvertedFrom {
case nil:
return nil, nil
case 0:
return "0", nil
}
result := convertToBase(valConvertedFrom, to)
if result == "" {
return nil, nil
}
return strings.ToUpper(result), nil
}
// Resolved implements the Expression interface.
func (c *Conv) Resolved() bool {
return c.n.Resolved() && c.fromBase.Resolved() && c.toBase.Resolved()
}
// Children implements the Expression interface.
func (c *Conv) Children() []sql.Expression {
return []sql.Expression{c.n, c.fromBase, c.toBase}
}
// WithChildren implements the Expression interface.
func (c *Conv) WithChildren(children ...sql.Expression) (sql.Expression, error) {
if len(children) != 3 {
return nil, sql.ErrInvalidChildrenNumber.New(c, len(children), 3)
}
return NewConv(children[0], children[1], children[2]), nil
}
// convertFromBase returns nil if fromBase input is invalid, 0 if nVal input is invalid and converted result if nVal and fromBase inputs are valid.
// This conversion truncates nVal as its first subpart that is convertable.
// nVal is treated as unsigned except nVal is negative.
func convertFromBase(nVal string, fromBase interface{}) interface{} {
fromBase, err := types.Int64.Convert(fromBase)
if err != nil {
return nil
}
fromVal := int(math.Abs(float64(fromBase.(int64))))
if fromVal < 2 || fromVal > 36 {
return nil
}
negative := false
var upper string
var lower string
if nVal[0] == '-' {
negative = true
nVal = nVal[1:]
} else if nVal[0] == '+' {
nVal = nVal[1:]
}
// check for upper and lower bound for given fromBase
if negative {
upper = strconv.FormatInt(math.MaxInt64, fromVal)
lower = strconv.FormatInt(math.MinInt64, fromVal)
if len(nVal) > len(lower) {
nVal = lower
} else if len(nVal) > len(upper) {
nVal = upper
}
} else {
upper = strconv.FormatUint(math.MaxUint64, fromVal)
lower = "0"
if len(nVal) < len(lower) {
nVal = lower
} else if len(nVal) > len(upper) {
nVal = upper
}
}
truncate := false
result := uint64(0)
i := 1
for !truncate && i <= len(nVal) {
val, err := strconv.ParseUint(nVal[:i], fromVal, 64)
if err != nil {
truncate = true
return result
}
result = val
i++
}
if negative {
return int64(result) * -1
}
return result
}
// convertToBase returns result of whole CONV function in string format, empty string if to input is invalid.
// The sign of toBase decides whether result is formatted as signed or unsigned.
func convertToBase(val interface{}, toBase interface{}) string {
toBase, err := types.Int64.Convert(toBase)
if err != nil {
return ""
}
toVal := int(math.Abs(float64(toBase.(int64))))
if toVal < 2 || toVal > 36 {
return ""
}
var result string
switch v := val.(type) {
case int64:
if toBase.(int64) < 0 {
result = strconv.FormatInt(v, toVal)
if err != nil {
return ""
}
} else {
result = strconv.FormatUint(uint64(v), toVal)
if err != nil {
return ""
}
}
case uint64:
if toBase.(int64) < 0 {
result = strconv.FormatInt(int64(v), toVal)
if err != nil {
return ""
}
} else {
result = strconv.FormatUint(v, toVal)
if err != nil {
return ""
}
}
}
return result
}