mirror of git://gcc.gnu.org/git/gcc.git
121 lines
3.3 KiB
Go
121 lines
3.3 KiB
Go
// Copyright 2015 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// This file implements encoding/decoding of Floats.
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package big
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import (
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"encoding/binary"
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"fmt"
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)
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// Gob codec version. Permits backward-compatible changes to the encoding.
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const floatGobVersion byte = 1
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// GobEncode implements the gob.GobEncoder interface.
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// The Float value and all its attributes (precision,
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// rounding mode, accuracy) are marshaled.
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func (x *Float) GobEncode() ([]byte, error) {
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if x == nil {
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return nil, nil
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}
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// determine max. space (bytes) required for encoding
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sz := 1 + 1 + 4 // version + mode|acc|form|neg (3+2+2+1bit) + prec
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n := 0 // number of mantissa words
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if x.form == finite {
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// add space for mantissa and exponent
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n = int((x.prec + (_W - 1)) / _W) // required mantissa length in words for given precision
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// actual mantissa slice could be shorter (trailing 0's) or longer (unused bits):
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// - if shorter, only encode the words present
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// - if longer, cut off unused words when encoding in bytes
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// (in practice, this should never happen since rounding
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// takes care of it, but be safe and do it always)
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if len(x.mant) < n {
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n = len(x.mant)
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}
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// len(x.mant) >= n
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sz += 4 + n*_S // exp + mant
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}
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buf := make([]byte, sz)
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buf[0] = floatGobVersion
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b := byte(x.mode&7)<<5 | byte((x.acc+1)&3)<<3 | byte(x.form&3)<<1
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if x.neg {
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b |= 1
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}
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buf[1] = b
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binary.BigEndian.PutUint32(buf[2:], x.prec)
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if x.form == finite {
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binary.BigEndian.PutUint32(buf[6:], uint32(x.exp))
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x.mant[len(x.mant)-n:].bytes(buf[10:]) // cut off unused trailing words
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}
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return buf, nil
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}
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// GobDecode implements the gob.GobDecoder interface.
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// The result is rounded per the precision and rounding mode of
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// z unless z's precision is 0, in which case z is set exactly
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// to the decoded value.
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func (z *Float) GobDecode(buf []byte) error {
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if len(buf) == 0 {
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// Other side sent a nil or default value.
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*z = Float{}
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return nil
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}
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if buf[0] != floatGobVersion {
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return fmt.Errorf("Float.GobDecode: encoding version %d not supported", buf[0])
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}
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oldPrec := z.prec
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oldMode := z.mode
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b := buf[1]
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z.mode = RoundingMode((b >> 5) & 7)
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z.acc = Accuracy((b>>3)&3) - 1
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z.form = form((b >> 1) & 3)
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z.neg = b&1 != 0
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z.prec = binary.BigEndian.Uint32(buf[2:])
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if z.form == finite {
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z.exp = int32(binary.BigEndian.Uint32(buf[6:]))
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z.mant = z.mant.setBytes(buf[10:])
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}
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if oldPrec != 0 {
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z.mode = oldMode
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z.SetPrec(uint(oldPrec))
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}
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return nil
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}
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// MarshalText implements the encoding.TextMarshaler interface.
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// Only the Float value is marshaled (in full precision), other
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// attributes such as precision or accuracy are ignored.
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func (x *Float) MarshalText() (text []byte, err error) {
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if x == nil {
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return []byte("<nil>"), nil
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}
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var buf []byte
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return x.Append(buf, 'g', -1), nil
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}
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// UnmarshalText implements the encoding.TextUnmarshaler interface.
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// The result is rounded per the precision and rounding mode of z.
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// If z's precision is 0, it is changed to 64 before rounding takes
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// effect.
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func (z *Float) UnmarshalText(text []byte) error {
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// TODO(gri): get rid of the []byte/string conversion
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_, _, err := z.Parse(string(text), 0)
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if err != nil {
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err = fmt.Errorf("math/big: cannot unmarshal %q into a *big.Float (%v)", text, err)
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}
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return err
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}
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