codekingpro/portable-devtools

1// Copyright 2015 The Go Authors. All rights reserved.2// Use of this source code is governed by a BSD-style3// license that can be found in the LICENSE file.4 5// This file implements encoding/decoding of Floats.6 7package big8 9import (10	"errors"11	"fmt"12	"internal/byteorder"13)14 15// Gob codec version. Permits backward-compatible changes to the encoding.16const floatGobVersion byte = 117 18// GobEncode implements the [encoding/gob.GobEncoder] interface.19// The [Float] value and all its attributes (precision,20// rounding mode, accuracy) are marshaled.21func (x *Float) GobEncode() ([]byte, error) {22	if x == nil {23		return nil, nil24	}25 26	// determine max. space (bytes) required for encoding27	sz := 1 + 1 + 4 // version + mode|acc|form|neg (3+2+2+1bit) + prec28	n := 0          // number of mantissa words29	if x.form == finite {30		// add space for mantissa and exponent31		n = int((x.prec + (_W - 1)) / _W) // required mantissa length in words for given precision32		// actual mantissa slice could be shorter (trailing 0's) or longer (unused bits):33		// - if shorter, only encode the words present34		// - if longer, cut off unused words when encoding in bytes35		//   (in practice, this should never happen since rounding36		//   takes care of it, but be safe and do it always)37		if len(x.mant) < n {38			n = len(x.mant)39		}40		// len(x.mant) >= n41		sz += 4 + n*_S // exp + mant42	}43	buf := make([]byte, sz)44 45	buf[0] = floatGobVersion46	b := byte(x.mode&7)<<5 | byte((x.acc+1)&3)<<3 | byte(x.form&3)<<147	if x.neg {48		b |= 149	}50	buf[1] = b51	byteorder.BEPutUint32(buf[2:], x.prec)52 53	if x.form == finite {54		byteorder.BEPutUint32(buf[6:], uint32(x.exp))55		x.mant[len(x.mant)-n:].bytes(buf[10:]) // cut off unused trailing words56	}57 58	return buf, nil59}60 61// GobDecode implements the [encoding/gob.GobDecoder] interface.62// The result is rounded per the precision and rounding mode of63// z unless z's precision is 0, in which case z is set exactly64// to the decoded value.65func (z *Float) GobDecode(buf []byte) error {66	if len(buf) == 0 {67		// Other side sent a nil or default value.68		*z = Float{}69		return nil70	}71	if len(buf) < 6 {72		return errors.New("Float.GobDecode: buffer too small")73	}74 75	if buf[0] != floatGobVersion {76		return fmt.Errorf("Float.GobDecode: encoding version %d not supported", buf[0])77	}78 79	oldPrec := z.prec80	oldMode := z.mode81 82	b := buf[1]83	z.mode = RoundingMode((b >> 5) & 7)84	z.acc = Accuracy((b>>3)&3) - 185	z.form = form((b >> 1) & 3)86	z.neg = b&1 != 087	z.prec = byteorder.BEUint32(buf[2:])88 89	if z.form == finite {90		if len(buf) < 10 {91			return errors.New("Float.GobDecode: buffer too small for finite form float")92		}93		z.exp = int32(byteorder.BEUint32(buf[6:]))94		z.mant = z.mant.setBytes(buf[10:])95	}96 97	if oldPrec != 0 {98		z.mode = oldMode99		z.SetPrec(uint(oldPrec))100	}101 102	if msg := z.validate0(); msg != "" {103		return errors.New("Float.GobDecode: " + msg)104	}105 106	return nil107}108 109// AppendText implements the [encoding.TextAppender] interface.110// Only the [Float] value is marshaled (in full precision), other111// attributes such as precision or accuracy are ignored.112func (x *Float) AppendText(b []byte) ([]byte, error) {113	if x == nil {114		return append(b, "<nil>"...), nil115	}116	return x.Append(b, 'g', -1), nil117}118 119// MarshalText implements the [encoding.TextMarshaler] interface.120// Only the [Float] value is marshaled (in full precision), other121// attributes such as precision or accuracy are ignored.122func (x *Float) MarshalText() (text []byte, err error) {123	return x.AppendText(nil)124}125 126// UnmarshalText implements the [encoding.TextUnmarshaler] interface.127// The result is rounded per the precision and rounding mode of z.128// If z's precision is 0, it is changed to 64 before rounding takes129// effect.130func (z *Float) UnmarshalText(text []byte) error {131	// TODO(gri): get rid of the []byte/string conversion132	_, _, err := z.Parse(string(text), 0)133	if err != nil {134		err = fmt.Errorf("math/big: cannot unmarshal %q into a *big.Float (%v)", text, err)135	}136	return err137}138