File size: 3,975 Bytes
e36aeda | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 | // Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// This file implements encoding/decoding of Floats.
package big
import (
"errors"
"fmt"
"internal/byteorder"
)
// Gob codec version. Permits backward-compatible changes to the encoding.
const floatGobVersion byte = 1
// GobEncode implements the [encoding/gob.GobEncoder] interface.
// The [Float] value and all its attributes (precision,
// rounding mode, accuracy) are marshaled.
func (x *Float) GobEncode() ([]byte, error) {
if x == nil {
return nil, nil
}
// determine max. space (bytes) required for encoding
sz := 1 + 1 + 4 // version + mode|acc|form|neg (3+2+2+1bit) + prec
n := 0 // number of mantissa words
if x.form == finite {
// add space for mantissa and exponent
n = int((x.prec + (_W - 1)) / _W) // required mantissa length in words for given precision
// actual mantissa slice could be shorter (trailing 0's) or longer (unused bits):
// - if shorter, only encode the words present
// - if longer, cut off unused words when encoding in bytes
// (in practice, this should never happen since rounding
// takes care of it, but be safe and do it always)
if len(x.mant) < n {
n = len(x.mant)
}
// len(x.mant) >= n
sz += 4 + n*_S // exp + mant
}
buf := make([]byte, sz)
buf[0] = floatGobVersion
b := byte(x.mode&7)<<5 | byte((x.acc+1)&3)<<3 | byte(x.form&3)<<1
if x.neg {
b |= 1
}
buf[1] = b
byteorder.BEPutUint32(buf[2:], x.prec)
if x.form == finite {
byteorder.BEPutUint32(buf[6:], uint32(x.exp))
x.mant[len(x.mant)-n:].bytes(buf[10:]) // cut off unused trailing words
}
return buf, nil
}
// GobDecode implements the [encoding/gob.GobDecoder] interface.
// The result is rounded per the precision and rounding mode of
// z unless z's precision is 0, in which case z is set exactly
// to the decoded value.
func (z *Float) GobDecode(buf []byte) error {
if len(buf) == 0 {
// Other side sent a nil or default value.
*z = Float{}
return nil
}
if len(buf) < 6 {
return errors.New("Float.GobDecode: buffer too small")
}
if buf[0] != floatGobVersion {
return fmt.Errorf("Float.GobDecode: encoding version %d not supported", buf[0])
}
oldPrec := z.prec
oldMode := z.mode
b := buf[1]
z.mode = RoundingMode((b >> 5) & 7)
z.acc = Accuracy((b>>3)&3) - 1
z.form = form((b >> 1) & 3)
z.neg = b&1 != 0
z.prec = byteorder.BEUint32(buf[2:])
if z.form == finite {
if len(buf) < 10 {
return errors.New("Float.GobDecode: buffer too small for finite form float")
}
z.exp = int32(byteorder.BEUint32(buf[6:]))
z.mant = z.mant.setBytes(buf[10:])
}
if oldPrec != 0 {
z.mode = oldMode
z.SetPrec(uint(oldPrec))
}
if msg := z.validate0(); msg != "" {
return errors.New("Float.GobDecode: " + msg)
}
return nil
}
// AppendText implements the [encoding.TextAppender] interface.
// Only the [Float] value is marshaled (in full precision), other
// attributes such as precision or accuracy are ignored.
func (x *Float) AppendText(b []byte) ([]byte, error) {
if x == nil {
return append(b, "<nil>"...), nil
}
return x.Append(b, 'g', -1), nil
}
// MarshalText implements the [encoding.TextMarshaler] interface.
// Only the [Float] value is marshaled (in full precision), other
// attributes such as precision or accuracy are ignored.
func (x *Float) MarshalText() (text []byte, err error) {
return x.AppendText(nil)
}
// UnmarshalText implements the [encoding.TextUnmarshaler] interface.
// The result is rounded per the precision and rounding mode of z.
// If z's precision is 0, it is changed to 64 before rounding takes
// effect.
func (z *Float) UnmarshalText(text []byte) error {
// TODO(gri): get rid of the []byte/string conversion
_, _, err := z.Parse(string(text), 0)
if err != nil {
err = fmt.Errorf("math/big: cannot unmarshal %q into a *big.Float (%v)", text, err)
}
return err
}
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