init formula calculation engine, ref #65 and #599

6 files changed, 788 insertions, 19 deletions

diff --git a/calc.go b/calc.go
new file mode 100644
index 0000000..d962fd4
--- /dev/null
+++ b/calc.go
@@ -0,0 +1,605 @@
+// Copyright 2016 - 2020 The excelize Authors. All rights reserved. Use of
+// this source code is governed by a BSD-style license that can be found in
+// the LICENSE file.
+//
+// Package excelize providing a set of functions that allow you to write to
+// and read from XLSX / XLSM / XLTM files. Supports reading and writing
+// spreadsheet documents generated by Microsoft Exce™ 2007 and later. Supports
+// complex components by high compatibility, and provided streaming API for
+// generating or reading data from a worksheet with huge amounts of data. This
+// library needs Go version 1.10 or later.
+
+package excelize
+
+import (
+	"container/list"
+	"errors"
+	"fmt"
+	"math"
+	"reflect"
+	"strconv"
+	"strings"
+
+	"github.com/xuri/efp"
+)
+
+// Excel formula errors
+const (
+	formulaErrorDIV         = "#DIV/0!"
+	formulaErrorNAME        = "#NAME?"
+	formulaErrorNA          = "#N/A"
+	formulaErrorNUM         = "#NUM!"
+	formulaErrorVALUE       = "#VALUE!"
+	formulaErrorREF         = "#REF!"
+	formulaErrorNULL        = "#NULL"
+	formulaErrorSPILL       = "#SPILL!"
+	formulaErrorCALC        = "#CALC!"
+	formulaErrorGETTINGDATA = "#GETTING_DATA"
+)
+
+// cellRef defines the structure of a cell reference
+type cellRef struct {
+	Col   int
+	Row   int
+	Sheet string
+}
+
+// cellRef defines the structure of a cell range
+type cellRange struct {
+	From cellRef
+	To   cellRef
+}
+
+type formulaFuncs struct{}
+
+// CalcCellValue provides a function to get calculated cell value. This
+// feature is currently in beta. Array formula, table formula and some other
+// formulas are not supported currently.
+func (f *File) CalcCellValue(sheet, cell string) (result string, err error) {
+	var (
+		formula string
+		token   efp.Token
+	)
+	if formula, err = f.GetCellFormula(sheet, cell); err != nil {
+		return
+	}
+	ps := efp.ExcelParser()
+	tokens := ps.Parse(formula)
+	if tokens == nil {
+		return
+	}
+	if token, err = f.evalInfixExp(sheet, tokens); err != nil {
+		return
+	}
+	result = token.TValue
+	return
+}
+
+// getPriority calculate arithmetic operator priority.
+func getPriority(token efp.Token) (pri int) {
+	var priority = map[string]int{
+		"*": 2,
+		"/": 2,
+		"+": 1,
+		"-": 1,
+	}
+	pri, _ = priority[token.TValue]
+	if token.TValue == "-" && token.TType == efp.TokenTypeOperatorPrefix {
+		pri = 3
+	}
+	if token.TSubType == efp.TokenSubTypeStart && token.TType == efp.TokenTypeSubexpression { // (
+		pri = 0
+	}
+	return
+}
+
+// evalInfixExp evaluate syntax analysis by given infix expression after
+// lexical analysis. Evaluate an infix expression containing formulas by
+// stacks:
+//
+//    opd  - Operand
+//    opt  - Operator
+//    opf  - Operation formula
+//    opfd - Operand of the operation formula
+//    opft - Operator of the operation formula
+//    args - Arguments of the operation formula
+//
+func (f *File) evalInfixExp(sheet string, tokens []efp.Token) (efp.Token, error) {
+	var err error
+	opdStack, optStack, opfStack, opfdStack, opftStack, argsStack := NewStack(), NewStack(), NewStack(), NewStack(), NewStack(), NewStack()
+	for i := 0; i < len(tokens); i++ {
+		token := tokens[i]
+
+		// out of function stack
+		if opfStack.Len() == 0 {
+			if err = f.parseToken(sheet, token, opdStack, optStack); err != nil {
+				return efp.Token{}, err
+			}
+		}
+
+		// function start
+		if token.TType == efp.TokenTypeFunction && token.TSubType == efp.TokenSubTypeStart {
+			opfStack.Push(token)
+			continue
+		}
+
+		// in function stack, walk 2 token at once
+		if opfStack.Len() > 0 {
+			var nextToken efp.Token
+			if i+1 < len(tokens) {
+				nextToken = tokens[i+1]
+			}
+
+			// current token is args or range, skip next token, order required: parse reference first
+			if token.TSubType == efp.TokenSubTypeRange {
+				if !opftStack.Empty() {
+					// parse reference: must reference at here
+					result, err := f.parseReference(sheet, token.TValue)
+					if err != nil {
+						return efp.Token{TValue: formulaErrorNAME}, err
+					}
+					if len(result) != 1 {
+						return efp.Token{}, errors.New(formulaErrorVALUE)
+					}
+					opfdStack.Push(efp.Token{
+						TType:    efp.TokenTypeOperand,
+						TSubType: efp.TokenSubTypeNumber,
+						TValue:   result[0],
+					})
+					continue
+				}
+				if nextToken.TType == efp.TokenTypeArgument || nextToken.TType == efp.TokenTypeFunction {
+					// parse reference: reference or range at here
+					result, err := f.parseReference(sheet, token.TValue)
+					if err != nil {
+						return efp.Token{TValue: formulaErrorNAME}, err
+					}
+					for _, val := range result {
+						argsStack.Push(efp.Token{
+							TType:    efp.TokenTypeOperand,
+							TSubType: efp.TokenSubTypeNumber,
+							TValue:   val,
+						})
+					}
+					if len(result) == 0 {
+						return efp.Token{}, errors.New(formulaErrorVALUE)
+					}
+					continue
+				}
+			}
+
+			// check current token is opft
+			if err = f.parseToken(sheet, token, opfdStack, opftStack); err != nil {
+				return efp.Token{}, err
+			}
+
+			// current token is arg
+			if token.TType == efp.TokenTypeArgument {
+				for !opftStack.Empty() {
+					// calculate trigger
+					topOpt := opftStack.Peek().(efp.Token)
+					if err := calculate(opfdStack, topOpt); err != nil {
+						return efp.Token{}, err
+					}
+					opftStack.Pop()
+				}
+				if !opfdStack.Empty() {
+					argsStack.Push(opfdStack.Pop())
+				}
+				continue
+			}
+
+			// current token is function stop
+			if token.TType == efp.TokenTypeFunction && token.TSubType == efp.TokenSubTypeStop {
+				for !opftStack.Empty() {
+					// calculate trigger
+					topOpt := opftStack.Peek().(efp.Token)
+					if err := calculate(opfdStack, topOpt); err != nil {
+						return efp.Token{}, err
+					}
+					opftStack.Pop()
+				}
+
+				// push opfd to args
+				if opfdStack.Len() > 0 {
+					argsStack.Push(opfdStack.Pop())
+				}
+				// call formula function to evaluate
+				result, err := callFuncByName(&formulaFuncs{}, opfStack.Peek().(efp.Token).TValue, []reflect.Value{reflect.ValueOf(argsStack)})
+				if err != nil {
+					return efp.Token{}, err
+				}
+				opfStack.Pop()
+				if opfStack.Len() > 0 { // still in function stack
+					opfdStack.Push(efp.Token{TValue: result, TType: efp.TokenTypeOperand, TSubType: efp.TokenSubTypeNumber})
+				} else {
+					opdStack.Push(efp.Token{TValue: result, TType: efp.TokenTypeOperand, TSubType: efp.TokenSubTypeNumber})
+				}
+			}
+		}
+	}
+	for optStack.Len() != 0 {
+		topOpt := optStack.Peek().(efp.Token)
+		if err = calculate(opdStack, topOpt); err != nil {
+			return efp.Token{}, err
+		}
+		optStack.Pop()
+	}
+	return opdStack.Peek().(efp.Token), err
+}
+
+// calculate evaluate basic arithmetic operations.
+func calculate(opdStack *Stack, opt efp.Token) error {
+	if opt.TValue == "-" && opt.TType == efp.TokenTypeOperatorPrefix {
+		opd := opdStack.Pop().(efp.Token)
+		opdVal, err := strconv.ParseFloat(opd.TValue, 64)
+		if err != nil {
+			return err
+		}
+		result := 0 - opdVal
+		opdStack.Push(efp.Token{TValue: fmt.Sprintf("%g", result), TType: efp.TokenTypeOperand, TSubType: efp.TokenSubTypeNumber})
+	}
+	if opt.TValue == "+" {
+		rOpd := opdStack.Pop().(efp.Token)
+		lOpd := opdStack.Pop().(efp.Token)
+		lOpdVal, err := strconv.ParseFloat(lOpd.TValue, 64)
+		if err != nil {
+			return err
+		}
+		rOpdVal, err := strconv.ParseFloat(rOpd.TValue, 64)
+		if err != nil {
+			return err
+		}
+		result := lOpdVal + rOpdVal
+		opdStack.Push(efp.Token{TValue: fmt.Sprintf("%g", result), TType: efp.TokenTypeOperand, TSubType: efp.TokenSubTypeNumber})
+	}
+	if opt.TValue == "-" && opt.TType == efp.TokenTypeOperatorInfix {
+		rOpd := opdStack.Pop().(efp.Token)
+		lOpd := opdStack.Pop().(efp.Token)
+		lOpdVal, err := strconv.ParseFloat(lOpd.TValue, 64)
+		if err != nil {
+			return err
+		}
+		rOpdVal, err := strconv.ParseFloat(rOpd.TValue, 64)
+		if err != nil {
+			return err
+		}
+		result := lOpdVal - rOpdVal
+		opdStack.Push(efp.Token{TValue: fmt.Sprintf("%g", result), TType: efp.TokenTypeOperand, TSubType: efp.TokenSubTypeNumber})
+	}
+	if opt.TValue == "*" {
+		rOpd := opdStack.Pop().(efp.Token)
+		lOpd := opdStack.Pop().(efp.Token)
+		lOpdVal, err := strconv.ParseFloat(lOpd.TValue, 64)
+		if err != nil {
+			return err
+		}
+		rOpdVal, err := strconv.ParseFloat(rOpd.TValue, 64)
+		if err != nil {
+			return err
+		}
+		result := lOpdVal * rOpdVal
+		opdStack.Push(efp.Token{TValue: fmt.Sprintf("%g", result), TType: efp.TokenTypeOperand, TSubType: efp.TokenSubTypeNumber})
+	}
+	if opt.TValue == "/" {
+		rOpd := opdStack.Pop().(efp.Token)
+		lOpd := opdStack.Pop().(efp.Token)
+		lOpdVal, err := strconv.ParseFloat(lOpd.TValue, 64)
+		if err != nil {
+			return err
+		}
+		rOpdVal, err := strconv.ParseFloat(rOpd.TValue, 64)
+		if err != nil {
+			return err
+		}
+		result := lOpdVal / rOpdVal
+		if rOpdVal == 0 {
+			return errors.New(formulaErrorDIV)
+		}
+		opdStack.Push(efp.Token{TValue: fmt.Sprintf("%g", result), TType: efp.TokenTypeOperand, TSubType: efp.TokenSubTypeNumber})
+	}
+	return nil
+}
+
+// parseToken parse basic arithmetic operator priority and evaluate based on
+// operators and operands.
+func (f *File) parseToken(sheet string, token efp.Token, opdStack, optStack *Stack) error {
+	// parse reference: must reference at here
+	if token.TSubType == efp.TokenSubTypeRange {
+		result, err := f.parseReference(sheet, token.TValue)
+		if err != nil {
+			return errors.New(formulaErrorNAME)
+		}
+		if len(result) != 1 {
+			return errors.New(formulaErrorVALUE)
+		}
+		token.TValue = result[0]
+		token.TType = efp.TokenTypeOperand
+		token.TSubType = efp.TokenSubTypeNumber
+	}
+	if (token.TValue == "-" && token.TType == efp.TokenTypeOperatorPrefix) || token.TValue == "+" || token.TValue == "-" || token.TValue == "*" || token.TValue == "/" {
+		if optStack.Len() == 0 {
+			optStack.Push(token)
+		} else {
+			tokenPriority := getPriority(token)
+			topOpt := optStack.Peek().(efp.Token)
+			topOptPriority := getPriority(topOpt)
+			if tokenPriority > topOptPriority {
+				optStack.Push(token)
+			} else {
+				for tokenPriority <= topOptPriority {
+					optStack.Pop()
+					if err := calculate(opdStack, topOpt); err != nil {
+						return err
+					}
+					if optStack.Len() > 0 {
+						topOpt = optStack.Peek().(efp.Token)
+						topOptPriority = getPriority(topOpt)
+						continue
+					}
+					break
+				}
+				optStack.Push(token)
+			}
+		}
+	}
+	if token.TType == efp.TokenTypeSubexpression && token.TSubType == efp.TokenSubTypeStart { // (
+		optStack.Push(token)
+	}
+	if token.TType == efp.TokenTypeSubexpression && token.TSubType == efp.TokenSubTypeStop { // )
+		for optStack.Peek().(efp.Token).TSubType != efp.TokenSubTypeStart && optStack.Peek().(efp.Token).TType != efp.TokenTypeSubexpression { // != (
+			topOpt := optStack.Peek().(efp.Token)
+			if err := calculate(opdStack, topOpt); err != nil {
+				return err
+			}
+			optStack.Pop()
+		}
+		optStack.Pop()
+	}
+	// opd
+	if token.TType == efp.TokenTypeOperand && token.TSubType == efp.TokenSubTypeNumber {
+		opdStack.Push(token)
+	}
+	return nil
+}
+
+// parseReference parse reference and extract values by given reference
+// characters and default sheet name.
+func (f *File) parseReference(sheet, reference string) (result []string, err error) {
+	reference = strings.Replace(reference, "$", "", -1)
+	refs, cellRanges, cellRefs := list.New(), list.New(), list.New()
+	for _, ref := range strings.Split(reference, ":") {
+		tokens := strings.Split(ref, "!")
+		cr := cellRef{}
+		if len(tokens) == 2 { // have a worksheet name
+			cr.Sheet = tokens[0]
+			if cr.Col, cr.Row, err = CellNameToCoordinates(tokens[1]); err != nil {
+				return
+			}
+			if refs.Len() > 0 {
+				e := refs.Back()
+				cellRefs.PushBack(e.Value.(cellRef))
+				refs.Remove(e)
+			}
+			refs.PushBack(cr)
+			continue
+		}
+		if cr.Col, cr.Row, err = CellNameToCoordinates(tokens[0]); err != nil {
+			return
+		}
+		e := refs.Back()
+		if e == nil {
+			cr.Sheet = sheet
+			refs.PushBack(cr)
+			continue
+		}
+		cellRanges.PushBack(cellRange{
+			From: e.Value.(cellRef),
+			To:   cr,
+		})
+		refs.Remove(e)
+	}
+	if refs.Len() > 0 {
+		e := refs.Back()
+		cellRefs.PushBack(e.Value.(cellRef))
+		refs.Remove(e)
+	}
+
+	result, err = f.rangeResolver(cellRefs, cellRanges)
+	return
+}
+
+// rangeResolver extract value as string from given reference and range list.
+// This function will not ignore the empty cell. Note that the result of 3D
+// range references may be different from Excel in some cases, for example,
+// A1:A2:A2:B3 in Excel will include B2, but we wont.
+func (f *File) rangeResolver(cellRefs, cellRanges *list.List) (result []string, err error) {
+	filter := map[string]string{}
+	// extract value from ranges
+	for temp := cellRanges.Front(); temp != nil; temp = temp.Next() {
+		cr := temp.Value.(cellRange)
+		if cr.From.Sheet != cr.To.Sheet {
+			err = errors.New(formulaErrorVALUE)
+		}
+		rng := []int{cr.From.Col, cr.From.Row, cr.To.Col, cr.To.Row}
+		sortCoordinates(rng)
+		for col := rng[0]; col <= rng[2]; col++ {
+			for row := rng[1]; row <= rng[3]; row++ {
+				var cell string
+				if cell, err = CoordinatesToCellName(col, row); err != nil {
+					return
+				}
+				if filter[cell], err = f.GetCellValue(cr.From.Sheet, cell); err != nil {
+					return
+				}
+			}
+		}
+	}
+	// extract value from references
+	for temp := cellRefs.Front(); temp != nil; temp = temp.Next() {
+		cr := temp.Value.(cellRef)
+		var cell string
+		if cell, err = CoordinatesToCellName(cr.Col, cr.Row); err != nil {
+			return
+		}
+		if filter[cell], err = f.GetCellValue(cr.Sheet, cell); err != nil {
+			return
+		}
+	}
+
+	for _, val := range filter {
+		result = append(result, val)
+	}
+	return
+}
+
+// callFuncByName calls the no error or only error return function with
+// reflect by given receiver, name and parameters.
+func callFuncByName(receiver interface{}, name string, params []reflect.Value) (result string, err error) {
+	function := reflect.ValueOf(receiver).MethodByName(name)
+	if function.IsValid() {
+		rt := function.Call(params)
+		if len(rt) == 0 {
+			return
+		}
+		if !rt[1].IsNil() {
+			err = rt[1].Interface().(error)
+			return
+		}
+		result = rt[0].Interface().(string)
+		return
+	}
+	err = fmt.Errorf("not support %s function", name)
+	return
+}
+
+// Math and Trigonometric functions
+
+// SUM function adds together a supplied set of numbers and returns the sum of
+// these values. The syntax of the function is:
+//
+//    SUM(number1,[number2],...)
+//
+func (fn *formulaFuncs) SUM(argsStack *Stack) (result string, err error) {
+	var val float64
+	var sum float64
+	for !argsStack.Empty() {
+		token := argsStack.Pop().(efp.Token)
+		if token.TValue == "" {
+			continue
+		}
+		val, err = strconv.ParseFloat(token.TValue, 64)
+		if err != nil {
+			return
+		}
+		sum += val
+	}
+	result = fmt.Sprintf("%g", sum)
+	return
+}
+
+// PRODUCT function returns the product (multiplication) of a supplied set of numerical values.
+// The syntax of the function is:
+//
+//    PRODUCT(number1,[number2],...)
+//
+func (fn *formulaFuncs) PRODUCT(argsStack *Stack) (result string, err error) {
+	var (
+		val     float64
+		product float64 = 1
+	)
+	for !argsStack.Empty() {
+		token := argsStack.Pop().(efp.Token)
+		if token.TValue == "" {
+			continue
+		}
+		val, err = strconv.ParseFloat(token.TValue, 64)
+		if err != nil {
+			return
+		}
+		product = product * val
+	}
+	result = fmt.Sprintf("%g", product)
+	return
+}
+
+// PRODUCT function calculates a given number, raised to a supplied power.
+// The syntax of the function is:
+//
+//    POWER(number,power)
+//
+func (fn *formulaFuncs) POWER(argsStack *Stack) (result string, err error) {
+	if argsStack.Len() != 2 {
+		err = errors.New("POWER requires 2 numeric arguments")
+		return
+	}
+	var x, y float64
+	y, err = strconv.ParseFloat(argsStack.Pop().(efp.Token).TValue, 64)
+	if err != nil {
+		return
+	}
+	x, err = strconv.ParseFloat(argsStack.Pop().(efp.Token).TValue, 64)
+	if err != nil {
+		return
+	}
+	if x == 0 && y == 0 {
+		err = errors.New(formulaErrorNUM)
+		return
+	}
+	if x == 0 && y < 0 {
+		err = errors.New(formulaErrorDIV)
+		return
+	}
+	result = fmt.Sprintf("%g", math.Pow(x, y))
+	return
+}
+
+// SQRT function calculates the positive square root of a supplied number.
+// The syntax of the function is:
+//
+//    SQRT(number)
+//
+func (fn *formulaFuncs) SQRT(argsStack *Stack) (result string, err error) {
+	if argsStack.Len() != 1 {
+		err = errors.New("SQRT requires 1 numeric arguments")
+		return
+	}
+	var val float64
+	val, err = strconv.ParseFloat(argsStack.Pop().(efp.Token).TValue, 64)
+	if err != nil {
+		return
+	}
+	if val < 0 {
+		err = errors.New(formulaErrorNUM)
+		return
+	}
+	result = fmt.Sprintf("%g", math.Sqrt(val))
+	return
+}
+
+// QUOTIENT function returns the integer portion of a division between two supplied numbers.
+// The syntax of the function is:
+//
+//   QUOTIENT(numerator,denominator)
+//
+func (fn *formulaFuncs) QUOTIENT(argsStack *Stack) (result string, err error) {
+	if argsStack.Len() != 2 {
+		err = errors.New("QUOTIENT requires 2 numeric arguments")
+		return
+	}
+	var x, y float64
+	y, err = strconv.ParseFloat(argsStack.Pop().(efp.Token).TValue, 64)
+	if err != nil {
+		return
+	}
+	x, err = strconv.ParseFloat(argsStack.Pop().(efp.Token).TValue, 64)
+	if err != nil {
+		return
+	}
+	if y == 0 {
+		err = errors.New(formulaErrorDIV)
+		return
+	}
+	result = fmt.Sprintf("%g", math.Trunc(x/y))
+	return
+}
diff --git a/calc_test.go b/calc_test.go
new file mode 100644
index 0000000..0ebe37e
--- /dev/null
+++ b/calc_test.go
@@ -0,0 +1,116 @@
+package excelize
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCalcCellValue(t *testing.T) {
+	prepareData := func() *File {
+		f := NewFile()
+		f.SetCellValue("Sheet1", "A1", 1)
+		f.SetCellValue("Sheet1", "A2", 2)
+		f.SetCellValue("Sheet1", "A3", 3)
+		f.SetCellValue("Sheet1", "A4", 0)
+		f.SetCellValue("Sheet1", "B1", 4)
+		return f
+	}
+
+	mathCalc := map[string]string{
+		"=SUM(1,2)":                           "3",
+		"=SUM(1,2+3)":                         "6",
+		"=SUM(SUM(1,2),2)":                    "5",
+		"=(-2-SUM(-4+7))*5":                   "-25",
+		"SUM(1,2,3,4,5,6,7)":                  "28",
+		"=SUM(1,2)+SUM(1,2)":                  "6",
+		"=1+SUM(SUM(1,2*3),4)":                "12",
+		"=1+SUM(SUM(1,-2*3),4)":               "0",
+		"=(-2-SUM(-4*(7+7)))*5":               "270",
+		"=SUM(SUM(1+2/1)*2-3/2,2)":            "6.5",
+		"=((3+5*2)+3)/5+(-6)/4*2+3":           "3.2",
+		"=1+SUM(SUM(1,2*3),4)*-4/2+5+(4+2)*3": "2",
+		"=1+SUM(SUM(1,2*3),4)*4/3+5+(4+2)*3":  "38.666666666666664",
+		// POWER
+		"=POWER(4,2)": "16",
+		// SQRT
+		"=SQRT(4)": "2",
+		// QUOTIENT
+		"=QUOTIENT(5, 2)":     "2",
+		"=QUOTIENT(4.5, 3.1)": "1",
+		"=QUOTIENT(-10, 3)":   "-3",
+	}
+	for formula, expected := range mathCalc {
+		f := prepareData()
+		assert.NoError(t, f.SetCellFormula("Sheet1", "C1", formula))
+		result, err := f.CalcCellValue("Sheet1", "C1")
+		assert.NoError(t, err)
+		assert.Equal(t, expected, result)
+	}
+	mathCalcError := map[string]string{
+		// POWER
+		"=POWER(0,0)":  "#NUM!",
+		"=POWER(0,-1)": "#DIV/0!",
+		"=POWER(1)":    "POWER requires 2 numeric arguments",
+		// SQRT
+		"=SQRT(-1)":  "#NUM!",
+		"=SQRT(1,2)": "SQRT requires 1 numeric arguments",
+		// QUOTIENT
+		"=QUOTIENT(1,0)": "#DIV/0!",
+		"=QUOTIENT(1)":   "QUOTIENT requires 2 numeric arguments",
+	}
+	for formula, expected := range mathCalcError {
+		f := prepareData()
+		assert.NoError(t, f.SetCellFormula("Sheet1", "C1", formula))
+		result, err := f.CalcCellValue("Sheet1", "C1")
+		assert.EqualError(t, err, expected)
+		assert.Equal(t, "", result)
+	}
+
+	referenceCalc := map[string]string{
+		"=A1/A3":                          "0.3333333333333333",
+		"=SUM(A1:A2)":                     "3",
+		"=SUM(Sheet1!A1,A2)":              "3",
+		"=(-2-SUM(-4+A2))*5":              "0",
+		"=SUM(Sheet1!A1:Sheet1!A1:A2,A2)": "5",
+		"=SUM(A1,A2,A3)*SUM(2,3)":         "30",
+		"=1+SUM(SUM(A1+A2/A3)*(2-3),2)":   "1.3333333333333335",
+		"=A1/A2/SUM(A1:A2:B1)":            "0.07142857142857142",
+		"=A1/A2/SUM(A1:A2:B1)*A3":         "0.21428571428571427",
+		// PRODUCT
+		"=PRODUCT(Sheet1!A1:Sheet1!A1:A2,A2)": "4",
+	}
+	for formula, expected := range referenceCalc {
+		f := prepareData()
+		assert.NoError(t, f.SetCellFormula("Sheet1", "C1", formula))
+		result, err := f.CalcCellValue("Sheet1", "C1")
+		assert.NoError(t, err)
+		assert.Equal(t, expected, result)
+	}
+
+	referenceCalcError := map[string]string{
+		"=1+SUM(SUM(A1+A2/A4)*(2-3),2)": "#DIV/0!",
+	}
+	for formula, expected := range referenceCalcError {
+		f := prepareData()
+		assert.NoError(t, f.SetCellFormula("Sheet1", "C1", formula))
+		result, err := f.CalcCellValue("Sheet1", "C1")
+		assert.EqualError(t, err, expected)
+		assert.Equal(t, "", result)
+	}
+
+	// Test get calculated cell value on not formula cell.
+	f := prepareData()
+	result, err := f.CalcCellValue("Sheet1", "A1")
+	assert.NoError(t, err)
+	assert.Equal(t, "", result)
+	// Test get calculated cell value on not exists worksheet.
+	f = prepareData()
+	_, err = f.CalcCellValue("SheetN", "A1")
+	assert.EqualError(t, err, "sheet SheetN is not exist")
+	// Test get calculated cell value with not support formula.
+	f = prepareData()
+	assert.NoError(t, f.SetCellFormula("Sheet1", "A1", "=UNSUPPORT(A1)"))
+	_, err = f.CalcCellValue("Sheet1", "A1")
+	assert.EqualError(t, err, "not support UNSUPPORT function")
+}
diff --git a/excelize.go b/excelize.go
index 73bc1b5..04e2e85 100644
--- a/excelize.go
+++ b/excelize.go
@@ -3,9 +3,11 @@
 // the LICENSE file.
 
 // Package excelize providing a set of functions that allow you to write to
-// and read from XLSX files. Support reads and writes XLSX file generated by
-// Microsoft Excel™ 2007 and later. Support save file without losing original
-// charts of XLSX. This library needs Go version 1.10 or later.
+// and read from XLSX / XLSM / XLTM files. Supports reading and writing
+// spreadsheet documents generated by Microsoft Exce™ 2007 and later. Supports
+// complex components by high compatibility, and provided streaming API for
+// generating or reading data from a worksheet with huge amounts of data. This
+// library needs Go version 1.10 or later.
 //
 // See https://xuri.me/excelize for more information about this package.
 package excelize
diff --git a/lib.go b/lib.go
index 83cdb4a..79c7cd4 100644
--- a/lib.go
+++ b/lib.go
@@ -12,6 +12,7 @@ package excelize
 import (
 	"archive/zip"
 	"bytes"
+	"container/list"
 	"fmt"
 	"io"
 	"log"
@@ -305,3 +306,48 @@ func genSheetPasswd(plaintext string) string {
 	password ^= 0xCE4B
 	return strings.ToUpper(strconv.FormatInt(password, 16))
 }
+
+// Stack defined an abstract data type that serves as a collection of elements.
+type Stack struct {
+	list *list.List
+}
+
+// NewStack create a new stack.
+func NewStack() *Stack {
+	list := list.New()
+	return &Stack{list}
+}
+
+// Push a value onto the top of the stack.
+func (stack *Stack) Push(value interface{}) {
+	stack.list.PushBack(value)
+}
+
+// Pop the top item of the stack and return it.
+func (stack *Stack) Pop() interface{} {
+	e := stack.list.Back()
+	if e != nil {
+		stack.list.Remove(e)
+		return e.Value
+	}
+	return nil
+}
+
+// Peek view the top item on the stack.
+func (stack *Stack) Peek() interface{} {
+	e := stack.list.Back()
+	if e != nil {
+		return e.Value
+	}
+	return nil
+}
+
+// Len return the number of items in the stack.
+func (stack *Stack) Len() int {
+	return stack.list.Len()
+}
+
+// Empty the stack.
+func (stack *Stack) Empty() bool {
+	return stack.list.Len() == 0
+}
diff --git a/sheet.go b/sheet.go
index 8c7f754..fa858af 100644
--- a/sheet.go
+++ b/sheet.go
@@ -211,10 +211,10 @@ func replaceRelationshipsBytes(content []byte) []byte {
 	return bytesReplace(content, oldXmlns, newXmlns, -1)
 }
 
-// SetActiveSheet provides function to set default active worksheet of XLSX by
-// given index. Note that active index is different from the index returned by
-// function GetSheetMap(). It should be greater or equal to 0 and less than
-// total worksheet numbers.
+// SetActiveSheet provides a function to set the default active sheet of the
+// workbook by a given index. Note that the active index is different from the
+// ID returned by function GetSheetMap(). It should be greater or equal to 0
+// and less than the total worksheet numbers.
 func (f *File) SetActiveSheet(index int) {
 	if index < 0 {
 		index = 0
@@ -327,9 +327,9 @@ func (f *File) getSheetNameByID(ID int) string {
 	return ""
 }
 
-// GetSheetName provides a function to get worksheet name of XLSX by given
-// worksheet index. If given sheet index is invalid, will return an empty
-// string.
+// GetSheetName provides a function to get the sheet name of the workbook by
+// the given sheet index. If the given sheet index is invalid, it will return
+// an empty string.
 func (f *File) GetSheetName(index int) (name string) {
 	for idx, sheet := range f.GetSheetList() {
 		if idx == index {
@@ -352,9 +352,9 @@ func (f *File) getSheetID(name string) int {
 	return ID
 }
 
-// GetSheetIndex provides a function to get worksheet index of XLSX by given
-// sheet name. If given worksheet name is invalid, will return an integer type
-// value -1.
+// GetSheetIndex provides a function to get a sheet index of the workbook by
+// the given sheet name. If the given sheet name is invalid, it will return an
+// integer type value -1.
 func (f *File) GetSheetIndex(name string) int {
 	var idx = -1
 	for index, sheet := range f.GetSheetList() {
@@ -365,8 +365,8 @@ func (f *File) GetSheetIndex(name string) int {
 	return idx
 }
 
-// GetSheetMap provides a function to get worksheet, chartsheet and
-// dialogsheet ID and name map of XLSX. For example:
+// GetSheetMap provides a function to get worksheets, chart sheets, dialog
+// sheets ID and name map of the workbook. For example:
 //
 //    f, err := excelize.OpenFile("Book1.xlsx")
 //    if err != nil {
@@ -387,8 +387,8 @@ func (f *File) GetSheetMap() map[int]string {
 	return sheetMap
 }
 
-// GetSheetList provides a function to get worksheet, chartsheet and
-// dialogsheet name list of workbook.
+// GetSheetList provides a function to get worksheets, chart sheets, and
+// dialog sheets name list of the workbook.
 func (f *File) GetSheetList() (list []string) {
 	wb := f.workbookReader()
 	if wb != nil {
diff --git a/xmlChartSheet.go b/xmlChartSheet.go
index fae5a16..30a0693 100644
--- a/xmlChartSheet.go
+++ b/xmlChartSheet.go
@@ -51,7 +51,7 @@ type xlsxChartsheetView struct {
 	XMLName            xml.Name      `xml:"sheetView"`
 	TabSelectedAttr    bool          `xml:"tabSelected,attr,omitempty"`
 	ZoomScaleAttr      uint32        `xml:"zoomScale,attr,omitempty"`
-	WorkbookViewIdAttr uint32        `xml:"workbookViewId,attr"`
+	WorkbookViewIDAttr uint32        `xml:"workbookViewId,attr"`
 	ZoomToFitAttr      bool          `xml:"zoomToFit,attr,omitempty"`
 	ExtLst             []*xlsxExtLst `xml:"extLst"`
 }
@@ -78,7 +78,7 @@ type xlsxCustomChartsheetViews struct {
 // xlsxCustomChartsheetView defines custom view properties for chart sheets.
 type xlsxCustomChartsheetView struct {
 	XMLName       xml.Name            `xml:"customChartsheetView"`
-	GuidAttr      string              `xml:"guid,attr"`
+	GUIDAttr      string              `xml:"guid,attr"`
 	ScaleAttr     uint32              `xml:"scale,attr,omitempty"`
 	StateAttr     string              `xml:"state,attr,omitempty"`
 	ZoomToFitAttr bool                `xml:"zoomToFit,attr,omitempty"`