Golang strconv.AppendFloat函數代碼示例

func (s *testFlusherSink) appendNumber(v interface{}) {
	switch n := v.(type) {
	case int:
		s.buf = strconv.AppendInt(s.buf, int64(n), 10)
	case uint:
		s.buf = strconv.AppendUint(s.buf, uint64(n), 10)
	case int64:
		s.buf = strconv.AppendInt(s.buf, n, 10)
	case uint64:
		s.buf = strconv.AppendUint(s.buf, n, 10)
	case int32:
		s.buf = strconv.AppendInt(s.buf, int64(n), 10)
	case uint32:
		s.buf = strconv.AppendUint(s.buf, uint64(n), 10)
	case int16:
		s.buf = strconv.AppendInt(s.buf, int64(n), 10)
	case uint16:
		s.buf = strconv.AppendUint(s.buf, uint64(n), 10)
	case int8:
		s.buf = strconv.AppendInt(s.buf, int64(n), 10)
	case uint8:
		s.buf = strconv.AppendUint(s.buf, uint64(n), 10)
	case float64:
		s.buf = strconv.AppendFloat(s.buf, n, 'f', -1, 64)
	case float32:
		s.buf = strconv.AppendFloat(s.buf, float64(n), 'f', -1, 32)
	}
}

func formatTextValue(value interface{}) ([]byte, error) {
	switch v := value.(type) {
	case int8:
		return strconv.AppendInt(nil, int64(v), 10), nil
	case int16:
		return strconv.AppendInt(nil, int64(v), 10), nil
	case int32:
		return strconv.AppendInt(nil, int64(v), 10), nil
	case int64:
		return strconv.AppendInt(nil, int64(v), 10), nil
	case int:
		return strconv.AppendInt(nil, int64(v), 10), nil
	case uint8:
		return strconv.AppendUint(nil, uint64(v), 10), nil
	case uint16:
		return strconv.AppendUint(nil, uint64(v), 10), nil
	case uint32:
		return strconv.AppendUint(nil, uint64(v), 10), nil
	case uint64:
		return strconv.AppendUint(nil, uint64(v), 10), nil
	case uint:
		return strconv.AppendUint(nil, uint64(v), 10), nil
	case float32:
		return strconv.AppendFloat(nil, float64(v), 'f', -1, 64), nil
	case float64:
		return strconv.AppendFloat(nil, float64(v), 'f', -1, 64), nil
	case []byte:
		return v, nil
	case string:
		return hack.Slice(v), nil
	default:
		return nil, errors.Errorf("invalid type %T", value)
	}
}

func (c *conn) appendNumber(v interface{}) {
	switch n := v.(type) {
	case int:
		c.buf = strconv.AppendInt(c.buf, int64(n), 10)
	case uint:
		c.buf = strconv.AppendUint(c.buf, uint64(n), 10)
	case int64:
		c.buf = strconv.AppendInt(c.buf, n, 10)
	case uint64:
		c.buf = strconv.AppendUint(c.buf, n, 10)
	case int32:
		c.buf = strconv.AppendInt(c.buf, int64(n), 10)
	case uint32:
		c.buf = strconv.AppendUint(c.buf, uint64(n), 10)
	case int16:
		c.buf = strconv.AppendInt(c.buf, int64(n), 10)
	case uint16:
		c.buf = strconv.AppendUint(c.buf, uint64(n), 10)
	case int8:
		c.buf = strconv.AppendInt(c.buf, int64(n), 10)
	case uint8:
		c.buf = strconv.AppendUint(c.buf, uint64(n), 10)
	case float64:
		c.buf = strconv.AppendFloat(c.buf, n, 'f', -1, 64)
	case float32:
		c.buf = strconv.AppendFloat(c.buf, float64(n), 'f', -1, 32)
	}
}

// appendEncodedText encodes item in text format as required by COPY
// and appends to buf
func appendEncodedText(parameterStatus *parameterStatus, buf []byte, x interface{}) []byte {
	switch v := x.(type) {
	case int64:
		return strconv.AppendInt(buf, v, 10)
	case float32:
		return strconv.AppendFloat(buf, float64(v), 'f', -1, 32)
	case float64:
		return strconv.AppendFloat(buf, v, 'f', -1, 64)
	case []byte:
		encodedBytea := encodeBytea(parameterStatus.serverVersion, v)
		return appendEscapedText(buf, string(encodedBytea))
	case string:
		return appendEscapedText(buf, v)
	case bool:
		return strconv.AppendBool(buf, v)
	case time.Time:
		return append(buf, v.Format(time.RFC3339Nano)...)
	case nil:
		return append(buf, "\\N"...)
	default:
		errorf("encode: unknown type for %T", v)
	}

	panic("not reached")
}

func dumpTextValue(mysqlType uint8, value types.Datum) ([]byte, error) {
	switch value.Kind() {
	case types.KindInt64:
		return strconv.AppendInt(nil, value.GetInt64(), 10), nil
	case types.KindUint64:
		return strconv.AppendUint(nil, value.GetUint64(), 10), nil
	case types.KindFloat32:
		return strconv.AppendFloat(nil, value.GetFloat64(), 'f', -1, 32), nil
	case types.KindFloat64:
		return strconv.AppendFloat(nil, value.GetFloat64(), 'f', -1, 64), nil
	case types.KindString, types.KindBytes:
		return value.GetBytes(), nil
	case types.KindMysqlTime:
		return hack.Slice(value.GetMysqlTime().String()), nil
	case types.KindMysqlDuration:
		return hack.Slice(value.GetMysqlDuration().String()), nil
	case types.KindMysqlDecimal:
		return hack.Slice(value.GetMysqlDecimal().String()), nil
	case types.KindMysqlEnum:
		return hack.Slice(value.GetMysqlEnum().String()), nil
	case types.KindMysqlSet:
		return hack.Slice(value.GetMysqlSet().String()), nil
	case types.KindMysqlBit:
		return hack.Slice(value.GetMysqlBit().ToString()), nil
	case types.KindMysqlHex:
		return hack.Slice(value.GetMysqlHex().ToString()), nil
	default:
		return nil, errInvalidType.Gen("invalid type %T", value)
	}
}

func appendField(b []byte, k string, v interface{}) []byte {
	b = append(b, []byte(escape.String(k))...)
	b = append(b, '=')

	// check popular types first
	switch v := v.(type) {
	case float64:
		b = strconv.AppendFloat(b, v, 'f', -1, 64)
	case int64:
		b = strconv.AppendInt(b, v, 10)
		b = append(b, 'i')
	case string:
		b = append(b, '"')
		b = append(b, []byte(EscapeStringField(v))...)
		b = append(b, '"')
	case bool:
		b = strconv.AppendBool(b, v)
	case int32:
		b = strconv.AppendInt(b, int64(v), 10)
		b = append(b, 'i')
	case int16:
		b = strconv.AppendInt(b, int64(v), 10)
		b = append(b, 'i')
	case int8:
		b = strconv.AppendInt(b, int64(v), 10)
		b = append(b, 'i')
	case int:
		b = strconv.AppendInt(b, int64(v), 10)
		b = append(b, 'i')
	case uint32:
		b = strconv.AppendInt(b, int64(v), 10)
		b = append(b, 'i')
	case uint16:
		b = strconv.AppendInt(b, int64(v), 10)
		b = append(b, 'i')
	case uint8:
		b = strconv.AppendInt(b, int64(v), 10)
		b = append(b, 'i')
	// TODO: 'uint' should be considered just as "dangerous" as a uint64,
	// perhaps the value should be checked and capped at MaxInt64? We could
	// then include uint64 as an accepted value
	case uint:
		b = strconv.AppendInt(b, int64(v), 10)
		b = append(b, 'i')
	case float32:
		b = strconv.AppendFloat(b, float64(v), 'f', -1, 32)
	case []byte:
		b = append(b, v...)
	case nil:
		// skip
	default:
		// Can't determine the type, so convert to string
		b = append(b, '"')
		b = append(b, []byte(EscapeStringField(fmt.Sprintf("%v", v)))...)
		b = append(b, '"')

	}

	return b
}

func ExampleAppendFloat() {
	b32 := []byte("float32:")
	b32 = strconv.AppendFloat(b32, 3.1415926535, 'E', -1, 32)
	fmt.Println(string(b32))

	b64 := []byte("float64:")
	b64 = strconv.AppendFloat(b64, 3.1415926535, 'E', -1, 64)
	fmt.Println(string(b64))

	// Output:
	// float32:3.1415927E+00
	// float64:3.1415926535E+00
}

/*
func AppendFloat(dst []byte, f float64, fmt byte, prec int, bitSize int) []byte

參數列表
dst 原列表
f 需要append到列表的浮點數
fmt 轉換格式 'b' 'e' 'E' 'f' 'g'或'G'
prec 浮點數精度
bitSize 32或64，32對應float32，64對應float64

返回值:
[]byte 返回列表

功能說明：
將浮點數f轉換為字符串值，並將轉換結果追加到dst的尾部，返回追加後的[]byte。
浮點數格式有'b' (-ddddp±ddd, 二進製指數), 'e' (-d.dddde±dd, 十進製指數), 'E' (-d.ddddE±dd, 十進製指數), 'f' (-ddd.dddd, 無指數), 'g' (大指數時相當於'e', 其他情況時相當於'f'), 'G' (大指數時相當於'E', 其他情況相當於'f').
精度用於控製當格式為'e' 'E' 'f' 'g' 'G'時除指數外的數字的個數；對於'e' 'E' 'f'指小數點後位數；對於'g' 'G'則表示總共的位數；如果使用-1，表示不改變數值的最小位數
*/
func main() {
	f := 100.123456789
	fmt.Println(f)
	c := strconv.AppendFloat(make([]byte, 0), f, 'f', 10, 32)
	fmt.Println(string(c))
	c = strconv.AppendFloat(make([]byte, 0), f, 'e', 10, 32)
	fmt.Println(string(c))
	c = strconv.AppendFloat(make([]byte, 0), f, 'f', 10, 64)
	fmt.Println(string(c))
	c = strconv.AppendFloat(make([]byte, 0), f, 'e', 10, 64)
	fmt.Println(string(c))

}

// submit an already sampled raw stat
func (s *Client) submit(stat, vprefix string, value interface{}, suffix string, rate float32) error {
	data := bufPool.Get()
	defer bufPool.Put(data)

	if s.prefix != "" {
		data.WriteString(s.prefix)
		data.WriteString(".")
	}

	data.WriteString(stat)
	data.WriteString(":")

	if vprefix != "" {
		data.WriteString(vprefix)
	}

	// sadly, no way to jam this back into the bytes.Buffer without
	// doing a few allocations... avoiding those is the whole point here...
	// so from here on out just use it as a raw []byte
	b := data.Bytes()

	switch v := value.(type) {
	case string:
		b = append(b, v...)
	case int64:
		b = strconv.AppendInt(b, v, 10)
	case float64:
		b = strconv.AppendFloat(b, v, 'f', -1, 64)
	default:
		return fmt.Errorf("No matching type format")
	}

	if suffix != "" {
		b = append(b, suffix...)
	}

	if s.rate != 0 && s.rate != 1 {
		rate *= s.rate
	}

	if rate < 1 {
		b = append(b, "|@"...)
		b = strconv.AppendFloat(b, float64(rate), 'f', 6, 32)
	}

	_, err := s.sender.Send(b)
	return err
}

func encode(parameterStatus *parameterStatus, x interface{}, pgtypOid oid.Oid) []byte {
	switch v := x.(type) {
	case int64:
		return strconv.AppendInt(nil, v, 10)
	case float64:
		return strconv.AppendFloat(nil, v, 'f', -1, 64)
	case []byte:
		if pgtypOid == oid.T_bytea {
			return encodeBytea(parameterStatus.serverVersion, v)
		}

		return v
	case string:
		if pgtypOid == oid.T_bytea {
			return encodeBytea(parameterStatus.serverVersion, []byte(v))
		}

		return []byte(v)
	case bool:
		return strconv.AppendBool(nil, v)
	case time.Time:
		return formatTs(v)

	default:
		errorf("encode: unknown type for %T", v)
	}

	panic("not reached")
}

func maxCellWidth(m Matrix, c rune, printed, prec int) ([]byte, int) {
	var (
		buf        = make([]byte, 0, 64)
		rows, cols = m.Dims()
		max        int
	)
	for i := 0; i < rows; i++ {
		if i >= printed-1 && i < rows-printed && 2*printed < rows {
			i = rows - printed - 1
			continue
		}
		for j := 0; j < cols; j++ {
			if j >= printed && j < cols-printed {
				continue
			}

			buf = strconv.AppendFloat(buf, m.At(i, j), byte(c), prec, 64)
			if len(buf) > max {
				max = len(buf)
			}
			buf = buf[:0]
		}
	}
	return buf, max
}

// EncodeSQLValue ...
func EncodeSQLValue(buf []byte, arg interface{}) ([]byte, error) {
	// Use sql.driver to convert the arg to a sql.Value which is simply
	// an interface{} with a restricted set of types. This also takes
	// care of using the sql.Valuer interface to convert arbitrary types
	// into sql.Values.
	dv, err := driver.DefaultParameterConverter.ConvertValue(arg)
	if err != nil {
		return nil, fmt.Errorf("converting query argument type: %v", err)
	}

	switch v := dv.(type) {
	case nil:
		return append(buf, nullstr...), nil
	case bool:
		if v {
			return append(buf, '1'), nil
		}
		return append(buf, '0'), nil
	case int64:
		return strconv.AppendInt(buf, v, 10), nil
	case float64:
		return strconv.AppendFloat(buf, v, 'f', -1, 64), nil
	case string:
		return encodeSQLString(buf, []byte(v)), nil
	case []byte:
		return encodeSQLBytes(buf, v), nil
	case time.Time:
		return encodeSQLString(buf, []byte(v.Format("2006-01-02 15:04:05"))), nil
	default:
		return nil, fmt.Errorf("unsupported bind variable type %T: %v", arg, arg)
	}
}

// formatFloat formats a float64; it is an efficient equivalent to  f.pad(strconv.FormatFloat()...).
func (f *fmt) formatFloat(v float64, verb byte, prec, n int) {
	// Format number, reserving space for leading + sign if needed.
	num := strconv.AppendFloat(f.intbuf[0:1], v, verb, prec, n)
	if num[1] == '-' || num[1] == '+' {
		num = num[1:]
	} else {
		num[0] = '+'
	}
	// num is now a signed version of the number.
	// If we're zero padding, want the sign before the leading zeros.
	// Achieve this by writing the sign out and then padding the unsigned number.
	if f.zero && f.widPresent && f.wid > len(num) {
		f.buf.WriteByte(num[0])
		f.wid--
		f.pad(num[1:])
		f.wid++ // Restore width; complex numbers will reuse this value for imaginary part.
		return
	}
	// f.space says to replace a leading + with a space.
	if f.space && num[0] == '+' {
		num[0] = ' '
		f.pad(num)
		return
	}
	// Now we know the sign is attached directly to the number, if present at all.
	// We want a sign if asked for, if it's negative, or if it's infinity (+Inf vs. -Inf).
	if f.plus || num[0] == '-' || math.IsInf(v, 0) {
		f.pad(num)
		return
	}
	// No sign to show and the number is positive; just print the unsigned number.
	f.pad(num[1:])
}

// formatFloat formats a float64; it is an efficient equivalent to  f.pad(strconv.FormatFloat()...).
func (f *fmt) formatFloat(v float64, verb byte, prec, n int) {
	// We leave one byte at the beginning of f.intbuf for a sign if needed,
	// and make it a space, which we might be able to use.
	f.intbuf[0] = ' '
	slice := strconv.AppendFloat(f.intbuf[0:1], v, verb, prec, n)
	// Add a plus sign or space to the floating-point string representation if missing and required.
	// The formatted number starts at slice[1].
	switch slice[1] {
	case '-', '+':
		// If we're zero padding, want the sign before the leading zeros.
		// Achieve this by writing the sign out and padding the postive number.
		if f.zero && f.widPresent && f.wid > len(slice) {
			f.buf.WriteByte(slice[1])
			f.wid--
			f.pad(slice[2:])
			return
		}
		// We're set; drop the leading space.
		slice = slice[1:]
	default:
		// There's no sign, but we might need one.
		if f.plus {
			slice[0] = '+'
		} else if f.space {
			// space is already there
		} else {
			slice = slice[1:]
		}
	}
	f.pad(slice)
}

func BenchmarkFloatToBytes1(b *testing.B) {
	r := []byte{} //make([]byte, 10)
	f := 123.456
	for i := 0; i < b.N; i++ {
		r = strconv.AppendFloat(r[:0], f, 'g', 6, 64)
	}
}