diff --git a/calc.go b/calc.go
index d2bab1dc..5b975f52 100644
--- a/calc.go
+++ b/calc.go
@@ -110,6 +110,7 @@ var tokenPriority = map[string]int{
 	"+":  3,
 	"-":  3,
 	"=":  2,
+	"<>": 2,
 	"<":  2,
 	"<=": 2,
 	">":  2,
@@ -151,11 +152,9 @@ func (f *File) CalcCellValue(sheet, cell string) (result string, err error) {
 		return
 	}
 	result = token.TValue
-	if len(result) > 16 {
-		num, e := roundPrecision(result)
-		if e != nil {
-			return result, err
-		}
+	isNum, precision := isNumeric(result)
+	if isNum && precision > 15 {
+		num, _ := roundPrecision(result)
 		result = strings.ToUpper(num)
 	}
 	return
@@ -353,6 +352,12 @@ func calcEq(rOpd, lOpd string, opdStack *Stack) error {
 	return nil
 }
 
+// calcNEq evaluate not equal arithmetic operations.
+func calcNEq(rOpd, lOpd string, opdStack *Stack) error {
+	opdStack.Push(efp.Token{TValue: strings.ToUpper(strconv.FormatBool(rOpd != lOpd)), TType: efp.TokenTypeOperand, TSubType: efp.TokenSubTypeNumber})
+	return nil
+}
+
 // calcL evaluate less than arithmetic operations.
 func calcL(rOpd, lOpd string, opdStack *Stack) error {
 	lOpdVal, err := strconv.ParseFloat(lOpd, 64)
@@ -498,6 +503,7 @@ func calculate(opdStack *Stack, opt efp.Token) error {
 		"/":  calcDiv,
 		"+":  calcAdd,
 		"=":  calcEq,
+		"<>": calcNEq,
 		"<":  calcL,
 		"<=": calcLe,
 		">":  calcG,
@@ -3400,6 +3406,20 @@ func (fn *formulaFuncs) CLEAN(argsList *list.List) (result string, err error) {
 	return
 }
 
+// LEN returns the length of a supplied text string. The syntax of the
+// function is:
+//
+//    LEN(text)
+//
+func (fn *formulaFuncs) LEN(argsList *list.List) (result string, err error) {
+	if argsList.Len() != 1 {
+		err = errors.New("LEN requires 1 string argument")
+		return
+	}
+	result = strconv.Itoa(len(argsList.Front().Value.(formulaArg).String))
+	return
+}
+
 // TRIM removes extra spaces (i.e. all spaces except for single spaces between
 // words or characters) from a supplied text string. The syntax of the
 // function is:
@@ -3469,3 +3489,43 @@ func (fn *formulaFuncs) UPPER(argsList *list.List) (result string, err error) {
 	result = strings.ToUpper(argsList.Front().Value.(formulaArg).String)
 	return
 }
+
+// Conditional Functions
+
+// IF function tests a supplied condition and returns one result if the
+// condition evaluates to TRUE, and another result if the condition evaluates
+// to FALSE. The syntax of the function is:
+//
+//    IF( logical_test, value_if_true, value_if_false )
+//
+func (fn *formulaFuncs) IF(argsList *list.List) (result string, err error) {
+	if argsList.Len() == 0 {
+		err = errors.New("IF requires at least 1 argument")
+		return
+	}
+	if argsList.Len() > 3 {
+		err = errors.New("IF accepts at most 3 arguments")
+		return
+	}
+	token := argsList.Front().Value.(formulaArg)
+	var cond bool
+	switch token.Type {
+	case ArgString:
+		if cond, err = strconv.ParseBool(token.String); err != nil {
+			err = errors.New(formulaErrorVALUE)
+			return
+		}
+		if argsList.Len() == 1 {
+			result = strings.ToUpper(strconv.FormatBool(cond))
+			return
+		}
+		if cond {
+			result = argsList.Front().Next().Value.(formulaArg).String
+			return
+		}
+		if argsList.Len() == 3 {
+			result = argsList.Back().Value.(formulaArg).String
+		}
+	}
+	return
+}
diff --git a/calc_test.go b/calc_test.go
index ea60a500..c9995403 100644
--- a/calc_test.go
+++ b/calc_test.go
@@ -323,13 +323,13 @@ func TestCalcCellValue(t *testing.T) {
 		"=ROUND(991,-1)":    "990",
 		// ROUNDDOWN
 		"=ROUNDDOWN(99.999,1)":   "99.9",
-		"=ROUNDDOWN(99.999,2)":   "99.99000000000001",
+		"=ROUNDDOWN(99.999,2)":   "99.99000000000002",
 		"=ROUNDDOWN(99.999,0)":   "99",
 		"=ROUNDDOWN(99.999,-1)":  "90",
-		"=ROUNDDOWN(-99.999,2)":  "-99.99000000000001",
+		"=ROUNDDOWN(-99.999,2)":  "-99.99000000000002",
 		"=ROUNDDOWN(-99.999,-1)": "-90",
-		// ROUNDUP
-		"=ROUNDUP(11.111,1)":   "11.200000000000003",
+		// ROUNDUP`
+		"=ROUNDUP(11.111,1)":   "11.200000000000001",
 		"=ROUNDUP(11.111,2)":   "11.120000000000003",
 		"=ROUNDUP(11.111,0)":   "12",
 		"=ROUNDUP(11.111,-1)":  "20",
@@ -467,6 +467,9 @@ func TestCalcCellValue(t *testing.T) {
 		// CLEAN
 		"=CLEAN(\"\u0009clean text\")": "clean text",
 		"=CLEAN(0)":                    "0",
+		// LEN
+		"=LEN(\"\")": "0",
+		"=LEN(D1)":   "5",
 		// TRIM
 		"=TRIM(\" trim text \")": "trim text",
 		"=TRIM(0)":               "0",
@@ -485,6 +488,12 @@ func TestCalcCellValue(t *testing.T) {
 		"=UPPER(\"TEST\")":     "TEST",
 		"=UPPER(\"Test\")":     "TEST",
 		"=UPPER(\"TEST 123\")": "TEST 123",
+		// Conditional Functions
+		// IF
+		"=IF(1=1)":                              "TRUE",
+		"=IF(1<>1)":                             "FALSE",
+		"=IF(5<0, \"negative\", \"positive\")":  "positive",
+		"=IF(-2<0, \"negative\", \"positive\")": "negative",
 	}
 	for formula, expected := range mathCalc {
 		f := prepareData()
@@ -805,6 +814,8 @@ func TestCalcCellValue(t *testing.T) {
 		// CLEAN
 		"=CLEAN()":    "CLEAN requires 1 argument",
 		"=CLEAN(1,2)": "CLEAN requires 1 argument",
+		// LEN
+		"=LEN()": "LEN requires 1 string argument",
 		// TRIM
 		"=TRIM()":    "TRIM requires 1 argument",
 		"=TRIM(1,2)": "TRIM requires 1 argument",
@@ -817,6 +828,11 @@ func TestCalcCellValue(t *testing.T) {
 		// PROPER
 		"=PROPER()":    "PROPER requires 1 argument",
 		"=PROPER(1,2)": "PROPER requires 1 argument",
+		// Conditional Functions
+		// IF
+		"=IF()":        "IF requires at least 1 argument",
+		"=IF(0,1,2,3)": "IF accepts at most 3 arguments",
+		"=IF(D1,1,2)":  "#VALUE!",
 	}
 	for formula, expected := range mathCalcError {
 		f := prepareData()
diff --git a/lib.go b/lib.go
index c89d69f0..3f135128 100644
--- a/lib.go
+++ b/lib.go
@@ -403,8 +403,8 @@ func (f *File) addNameSpaces(path string, ns xml.Attr) {
 	}
 }
 
-// setIgnorableNameSpace provides a function to set XML namespace as ignorable by the given
-// attribute.
+// setIgnorableNameSpace provides a function to set XML namespace as ignorable
+// by the given attribute.
 func (f *File) setIgnorableNameSpace(path string, index int, ns xml.Attr) {
 	ignorableNS := []string{"c14", "cdr14", "a14", "pic14", "x14", "xdr14", "x14ac", "dsp", "mso14", "dgm14", "x15", "x12ac", "x15ac", "xr", "xr2", "xr3", "xr4", "xr5", "xr6", "xr7", "xr8", "xr9", "xr10", "xr11", "xr12", "xr13", "xr14", "xr15", "x15", "x16", "x16r2", "mo", "mx", "mv", "o", "v"}
 	if inStrSlice(strings.Fields(f.xmlAttr[path][index].Value), ns.Name.Local) == -1 && inStrSlice(ignorableNS, ns.Name.Local) != -1 {
@@ -418,6 +418,29 @@ func (f *File) addSheetNameSpace(sheet string, ns xml.Attr) {
 	f.addNameSpaces(name, ns)
 }
 
+// isNumeric determines whether an expression is a valid numeric type and get
+// the precision for the numeric.
+func isNumeric(s string) (bool, int) {
+	dot := false
+	p := 0
+	for i, v := range s {
+		if v == '.' {
+			if dot {
+				return false, 0
+			}
+			dot = true
+		} else if v < '0' || v > '9' {
+			if i == 0 && v == '-' {
+				continue
+			}
+			return false, 0
+		} else if dot {
+			p++
+		}
+	}
+	return true, p
+}
+
 // Stack defined an abstract data type that serves as a collection of elements.
 type Stack struct {
 	list *list.List
diff --git a/rows.go b/rows.go
index 44c4b643..97cf2f59 100644
--- a/rows.go
+++ b/rows.go
@@ -20,7 +20,6 @@ import (
 	"log"
 	"math"
 	"strconv"
-	"strings"
 
 	"github.com/mohae/deepcopy"
 )
@@ -346,12 +345,9 @@ func (c *xlsxC) getValueFrom(f *File, d *xlsxSST) (string, error) {
 		}
 		return f.formattedValue(c.S, c.V), nil
 	default:
-		splited := strings.Split(c.V, ".")
-		if len(splited) == 2 && len(splited[1]) > 15 {
-			val, err := roundPrecision(c.V)
-			if err != nil {
-				return "", err
-			}
+		isNum, precision := isNumeric(c.V)
+		if isNum && precision > 15 {
+			val, _ := roundPrecision(c.V)
 			if val != c.V {
 				return f.formattedValue(c.S, val), nil
 			}
diff --git a/rows_test.go b/rows_test.go
index 02b00daf..73931aa3 100644
--- a/rows_test.go
+++ b/rows_test.go
@@ -835,9 +835,14 @@ func TestGetValueFromNumber(t *testing.T) {
 	assert.Equal(t, "2.22", val)
 
 	c = &xlsxC{T: "n", V: "2.220000ddsf0000000002-r"}
-	_, err = c.getValueFrom(f, d)
-	assert.NotNil(t, err)
-	assert.Equal(t, "strconv.ParseFloat: parsing \"2.220000ddsf0000000002-r\": invalid syntax", err.Error())
+	val, err = c.getValueFrom(f, d)
+	assert.NoError(t, err)
+	assert.Equal(t, "2.220000ddsf0000000002-r", val)
+
+	c = &xlsxC{T: "n", V: "2.2."}
+	val, err = c.getValueFrom(f, d)
+	assert.NoError(t, err)
+	assert.Equal(t, "2.2.", val)
 }
 
 func TestErrSheetNotExistError(t *testing.T) {