func testFrac(c *C, v mysql.Decimal) {
b := EncodeDecimal([]byte{}, v)
_, d, err := DecodeDecimal(b)
c.Assert(err, IsNil)
c.Assert(v.Equals(d), IsTrue)
c.Assert(v.FracDigits(), Equals, d.FracDigits())
c.Assert(v.String(), Equals, d.String())
}
// DecodeDecimal decodes bytes to decimal.
// DecodeFloat decodes a float from a byte slice
// Decimal decoding:
// Byte -> value sign
// DecodeInt -> exp value
// DecodeBytes -> abs value bytes
func DecodeDecimal(b []byte) ([]byte, mysql.Decimal, error) {
var (
r = b
d mysql.Decimal
err error
)
// Decode value sign.
valSign := int64(r[0])
r = r[1:]
if valSign == zeroSign {
d, err = mysql.ParseDecimal("0")
return r, d, errors.Trace(err)
}
// Decode exp value.
expVal := int64(0)
r, expVal, err = DecodeInt(r)
if err != nil {
return r, d, errors.Trace(err)
}
// Decode abs value bytes.
value := []byte{}
if valSign == negativeSign {
expVal = -expVal
r, value, err = DecodeBytesDesc(r)
} else {
r, value, err = DecodeBytes(r)
}
if err != nil {
return r, d, errors.Trace(err)
}
// Set decimal sign and point to value.
if valSign == negativeSign {
value = append([]byte("-0."), value...)
} else {
value = append([]byte("0."), value...)
}
numberDecimal, err := mysql.ParseDecimal(string(value))
if err != nil {
return r, d, errors.Trace(err)
}
expDecimal := mysql.NewDecimalFromInt(1, int32(expVal))
d = numberDecimal.Mul(expDecimal)
if expDecimal.Exponent() > 0 {
// For int64(3), it will be converted to value=0.3 and exp=1 when doing encode.
// Its frac will be changed after we run d = numberDecimal.Mul(expDecimal).
// So we try to get frac to the original one.
d.SetFracDigits(d.FracDigits() - expDecimal.Exponent())
}
return r, d, nil
}