add decimal and test case

math/big/helper.go

+package hessian
+
+import (
+	"github.com/pkg/errors"
+	"math"
+	"strings"
+	"unicode"
+)
+
+// RoundFloat rounds float val to the nearest integer value with float64 format, like MySQL Round function.
+// RoundFloat uses default rounding mode, see https://dev.mysql.com/doc/refman/5.7/en/precision-math-rounding.html
+// so rounding use "round half away from zero".
+// e.g, 1.5 -> 2, -1.5 -> -2.
+func RoundFloat(f float64) float64 {
+	if math.Abs(f) < 0.5 {
+		return 0
+	}
+
+	return math.Trunc(f + math.Copysign(0.5, f))
+}
+
+// Round rounds the argument f to dec decimal places.
+// dec defaults to 0 if not specified. dec can be negative
+// to cause dec digits left of the decimal point of the
+// value f to become zero.
+func Round(f float64, dec int) float64 {
+	shift := math.Pow10(dec)
+	tmp := f * shift
+	if math.IsInf(tmp, 0) {
+		return f
+	}
+	return RoundFloat(tmp) / shift
+}
+
+// Truncate truncates the argument f to dec decimal places.
+// dec defaults to 0 if not specified. dec can be negative
+// to cause dec digits left of the decimal point of the
+// value f to become zero.
+func Truncate(f float64, dec int) float64 {
+	shift := math.Pow10(dec)
+	tmp := f * shift
+	if math.IsInf(tmp, 0) {
+		return f
+	}
+	return math.Trunc(tmp) / shift
+}
+
+// GetMaxFloat gets the max float for given flen and decimal.
+func GetMaxFloat(flen int, decimal int) float64 {
+	intPartLen := flen - decimal
+	f := math.Pow10(intPartLen)
+	f -= math.Pow10(-decimal)
+	return f
+}
+
+// TruncateFloat tries to truncate f.
+// If the result exceeds the max/min float that flen/decimal allowed, returns the max/min float allowed.
+func TruncateFloat(f float64, flen int, decimal int) (float64, error) {
+	if math.IsNaN(f) {
+		// nan returns 0
+		//todo ErrOverflow.GenWithStackByArgs("DOUBLE", "")
+		return 0, nil
+	}
+
+	maxF := GetMaxFloat(flen, decimal)
+
+	if !math.IsInf(f, 0) {
+		f = Round(f, decimal)
+	}
+
+	var err error
+	if f > maxF {
+		f = maxF
+		//err = ErrOverflow.GenWithStackByArgs("DOUBLE", "")
+	} else if f < -maxF {
+		f = -maxF
+		//	err = ErrOverflow.GenWithStackByArgs("DOUBLE", "")
+	}
+	//todo errors.Trace(err)
+	return f, err
+}
+
+func isSpace(c byte) bool {
+	return c == ' ' || c == '\t'
+}
+
+func isDigit(c byte) bool {
+	return c >= '0' && c <= '9'
+}
+
+func myMax(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}
+
+func myMaxInt8(a, b int8) int8 {
+	if a > b {
+		return a
+	}
+	return b
+}
+
+func myMin(a, b int) int {
+	if a < b {
+		return a
+	}
+	return b
+}
+
+func myMinInt8(a, b int8) int8 {
+	if a < b {
+		return a
+	}
+	return b
+}
+
+const (
+	maxUint    = uint64(math.MaxUint64)
+	uintCutOff = maxUint/uint64(10) + 1
+	intCutOff  = uint64(math.MaxInt64) + 1
+)
+
+// strToInt converts a string to an integer in best effort.
+func strToInt(str string) (int64, error) {
+	str = strings.TrimSpace(str)
+	if len(str) == 0 {
+		//todo ErrTruncated
+		return 0, nil
+	}
+	negative := false
+	i := 0
+	if str[i] == '-' {
+		negative = true
+		i++
+	} else if str[i] == '+' {
+		i++
+	}
+
+	var (
+		err    error
+		hasNum = false
+	)
+	r := uint64(0)
+	for ; i < len(str); i++ {
+		if !unicode.IsDigit(rune(str[i])) {
+			//todo ErrTruncated
+
+			//			err = ErrTruncated
+			err = errors.Errorf("")
+			break
+		}
+		hasNum = true
+		if r >= uintCutOff {
+			r = 0
+			// todo err = errors.Trace(ErrBadNumber)
+			err = errors.Errorf("")
+			break
+		}
+		r = r * uint64(10)
+
+		r1 := r + uint64(str[i]-'0')
+		if r1 < r || r1 > maxUint {
+			r = 0
+			//todo err = errors.Trace(ErrBadNumber)
+			err = errors.Errorf("")
+			break
+		}
+		r = r1
+	}
+	if !hasNum {
+		//err = ErrTruncated
+	}
+
+	if !negative && r >= intCutOff {
+		//todo errors.Trace(ErrBadNumber)
+		return math.MaxInt64, nil
+	}
+
+	if negative && r > intCutOff {
+		//todo errors.Trace(ErrBadNumber)
+
+		return math.MinInt64, nil
+	}
+
+	if negative {
+		r = -r
+	}
+	return int64(r), err
+}