package mssql import ( "encoding/binary" "errors" "math" "math/big" ) // http://msdn.microsoft.com/en-us/library/ee780893.aspx type Decimal struct { integer [4]uint32 positive bool prec uint8 scale uint8 } var scaletblflt64 [39]float64 func (d Decimal) ToFloat64() float64 { val := float64(0) for i := 3; i >= 0; i-- { val *= 0x100000000 val += float64(d.integer[i]) } if !d.positive { val = -val } if d.scale != 0 { val /= scaletblflt64[d.scale] } return val } func Float64ToDecimal(f float64) (Decimal, error) { var dec Decimal if math.IsNaN(f) { return dec, errors.New("NaN") } if math.IsInf(f, 0) { return dec, errors.New("Infinity can't be converted to decimal") } dec.positive = f >= 0 if !dec.positive { f = math.Abs(f) } if f > 3.402823669209385e+38 { return dec, errors.New("Float value is out of range") } dec.prec = 20 var integer float64 for dec.scale = 0; dec.scale <= 20; dec.scale++ { integer = f * scaletblflt64[dec.scale] _, frac := math.Modf(integer) if frac == 0 { break } } for i := 0; i < 4; i++ { mod := math.Mod(integer, 0x100000000) integer -= mod integer /= 0x100000000 dec.integer[i] = uint32(mod) } return dec, nil } func init() { var acc float64 = 1 for i := 0; i <= 38; i++ { scaletblflt64[i] = acc acc *= 10 } } func (d Decimal) Bytes() []byte { bytes := make([]byte, 16) binary.BigEndian.PutUint32(bytes[0:4], d.integer[3]) binary.BigEndian.PutUint32(bytes[4:8], d.integer[2]) binary.BigEndian.PutUint32(bytes[8:12], d.integer[1]) binary.BigEndian.PutUint32(bytes[12:16], d.integer[0]) var x big.Int x.SetBytes(bytes) if !d.positive { x.Neg(&x) } return scaleBytes(x.String(), d.scale) } func scaleBytes(s string, scale uint8) []byte { z := make([]byte, 0, len(s)+1) if s[0] == '-' || s[0] == '+' { z = append(z, byte(s[0])) s = s[1:] } pos := len(s) - int(scale) if pos <= 0 { z = append(z, byte('0')) } else if pos > 0 { z = append(z, []byte(s[:pos])...) } if scale > 0 { z = append(z, byte('.')) for pos < 0 { z = append(z, byte('0')) pos++ } z = append(z, []byte(s[pos:])...) } return z } func (d Decimal) String() string { return string(d.Bytes()) }