forked from woodsbury/decimal128
/
scan.go
475 lines (393 loc) · 9.21 KB
/
scan.go
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package decimal128
import (
"errors"
"fmt"
"io"
"strconv"
)
// MustParse is like [Parse] but panics if the provided string cannot be parsed,
// instead of returning an error.
func MustParse(s string) Decimal {
d, err := parse(s, payloadOpMustParse)
if err != nil {
panic("decimal128.MustParse(" + strconv.Quote(s) + "): invalid syntax")
}
return d
}
// Parse parses a Decimal value from the string provided. Parse accepts decimal
// floating point syntax. An underscore character '_' may appear between digits
// as a separator. Parse also recognises the string "NaN", and the (possibly
// signed) strings "Inf" and "Infinity", as their respective special floating
// point values. It ignores case when matching.
//
// If s is not syntactically well-formed, Parse returns an error that can be
// compared to [strconv.ErrSyntax] via [errors.Is].
//
// If the value is too precise to fit in a Decimal the result is rounded using
// the [DefaultRoundingMode]. If the value is greater than the largest possible
// Decimal value, Parse returns ±Inf and an error that can be compared to
// [strconv.ErrRange] via [errors.Is].
func Parse(s string) (Decimal, error) {
return parse(s, payloadOpParse)
}
// Scan implements the [fmt.Scanner] interface. It supports the verbs 'e', 'E',
// 'f', 'F', 'g', 'G', and 'v'.
func (d *Decimal) Scan(f fmt.ScanState, verb rune) error {
switch verb {
case 'e', 'E', 'f', 'F', 'g', 'G', 'v':
default:
return errors.New("bad verb '%" + string(verb) + "' for Decimal")
}
f.SkipSpace()
r, _, err := f.ReadRune()
if err != nil {
if errors.Is(err, io.EOF) {
return io.ErrUnexpectedEOF
}
return err
}
neg := false
if r == '-' {
neg = true
} else if r != '+' {
f.UnreadRune()
}
r, _, err = f.ReadRune()
if err != nil {
if errors.Is(err, io.EOF) {
return io.ErrUnexpectedEOF
}
return err
}
if r == 'I' || r == 'i' {
r2, _, err := f.ReadRune()
if err != nil {
if errors.Is(err, io.EOF) {
return io.ErrUnexpectedEOF
}
return err
}
if r2 != 'N' && r2 != 'n' {
return &parseSyntaxError{s: string([]rune{r, r2})}
}
r3, _, err := f.ReadRune()
if err != nil {
if errors.Is(err, io.EOF) {
return io.ErrUnexpectedEOF
}
return err
}
if r3 != 'F' && r3 != 'f' {
return &parseSyntaxError{s: string([]rune{r, r2, r3})}
}
*d = inf(neg)
return nil
}
if r == 'N' || r == 'n' {
r2, _, err := f.ReadRune()
if err != nil {
if errors.Is(err, io.EOF) {
return io.ErrUnexpectedEOF
}
return err
}
if r2 != 'A' && r2 != 'a' {
return &parseSyntaxError{s: string([]rune{r, r2})}
}
r3, _, err := f.ReadRune()
if err != nil {
if errors.Is(err, io.EOF) {
return io.ErrUnexpectedEOF
}
return err
}
if r3 != 'N' && r3 != 'n' {
return &parseSyntaxError{s: string([]rune{r, r2, r3})}
}
*d = nan(payloadOpScan, 0, 0)
return nil
}
f.UnreadRune()
tok, err := f.Token(false, func(r rune) bool {
switch {
case r >= '0' && r <= '9':
return true
case r == '.':
return true
case r == 'E' || r == 'e':
return true
case r == '-':
return true
case r == '_':
return true
case r == '+':
return true
default:
return false
}
})
if err != nil {
return err
}
tmp, err := parseNumber(tok, neg, true)
if err != nil {
switch err := err.(type) {
case parseNumberRangeError:
return &parseRangeError{string(tok)}
case parseNumberSyntaxError:
return &parseSyntaxError{string(tok)}
default:
return err
}
}
*d = tmp
return nil
}
// UnmarshalText implements the [encoding.TextUnmarshaler] interface.
func (d *Decimal) UnmarshalText(data []byte) error {
tmp, err := parse(data, payloadOpUnmarshalText)
if err != nil {
return err
}
*d = tmp
return nil
}
func parse[D []byte | string](d D, op Payload) (Decimal, error) {
if len(d) == 0 {
return Decimal{}, &parseSyntaxError{}
}
s := d
neg := false
if d[0] == '+' {
d = d[1:]
} else if d[0] == '-' {
neg = true
d = d[1:]
}
l := len(d)
if l == 0 {
return Decimal{}, &parseSyntaxError{string(s)}
} else if l == 3 {
if (d[0] == 'I' || d[0] == 'i') && (d[1] == 'N' || d[1] == 'n') && (d[2] == 'F' || d[2] == 'f') {
return inf(neg), nil
}
if (d[0] == 'N' || d[0] == 'n') && (d[1] == 'A' || d[1] == 'a') && (d[2] == 'N' || d[2] == 'n') {
return nan(op, 0, 0), nil
}
} else if l == 8 {
if (d[0] == 'I' || d[0] == 'i') && (d[1] == 'N' || d[1] == 'n') && (d[2] == 'F' || d[2] == 'f') && (d[3] == 'I' || d[3] == 'i') && (d[4] == 'N' || d[4] == 'n') && (d[5] == 'I' || d[5] == 'i') && (d[6] == 'T' || d[6] == 't') && (d[7] == 'Y' || d[7] == 'y') {
return inf(neg), nil
}
}
v, err := parseNumber(d, neg, true)
if err != nil {
switch err := err.(type) {
case parseNumberRangeError:
return v, &parseRangeError{string(s)}
case parseNumberSyntaxError:
return v, &parseSyntaxError{string(s)}
default:
return v, err
}
}
return v, nil
}
func parseNumber[D []byte | string](d D, neg, sepallowed bool) (Decimal, error) {
var sig64 uint64
var nfrac int16
var trunc int8
caneof := false
cansep := false
cansgn := false
eneg := false
sawdig := false
sawdot := false
sawexp := false
l := len(d)
i := 0
for ; !sawexp && sig64 <= 0x18ff_ffff_ffff_ffff && i < l; i++ {
switch c := d[i]; true {
case c >= '0' && c <= '9':
caneof = true
cansep = true
cansgn = false
sawdig = true
sig64 = sig64*10 + uint64(c-'0')
if sawdot {
nfrac++
}
case c == '.':
if sawdot {
return Decimal{}, parseNumberSyntaxError{}
}
caneof = true
cansep = false
cansgn = false
sawdot = true
case c == 'E' || c == 'e':
if !sawdig {
return Decimal{}, parseNumberSyntaxError{}
}
caneof = false
cansep = false
cansgn = true
sawexp = true
case c == '_':
if !sepallowed || !cansep {
return Decimal{}, parseNumberSyntaxError{}
}
caneof = false
cansep = false
cansgn = false
default:
return Decimal{}, parseNumberSyntaxError{}
}
}
sig := uint128{sig64, 0}
var exp int16
maxexp := false
for ; i < l; i++ {
switch c := d[i]; true {
case c >= '0' && c <= '9':
caneof = true
cansep = true
cansgn = false
sawdig = true
if sawexp {
if exp > exponentBias/10+1 {
maxexp = true
}
exp *= 10
exp += int16(c - '0')
} else {
if sig[1] <= 0x18ff_ffff_ffff_ffff {
if sig[1] <= 0x027f_ffff_ffff_ffff && i < l-1 {
c2 := d[i+1]
if c2 >= '0' && c2 <= '9' {
sig = sig.mul64(100)
sig = sig.add64(uint64(c-'0')*10 + uint64(c2-'0'))
if sawdot {
nfrac += 2
}
i++
continue
}
}
sig = sig.mul64(10)
sig = sig.add64(uint64(c - '0'))
if sawdot {
nfrac++
}
} else {
if c != '0' {
trunc = 1
}
if !sawdot {
if exp < exponentBias+39 {
nfrac--
}
}
}
}
case c == '.':
if sawdot || sawexp {
return Decimal{}, parseNumberSyntaxError{}
}
caneof = true
cansep = false
cansgn = false
sawdot = true
case c == 'E' || c == 'e':
if !sawdig || sawexp {
return Decimal{}, parseNumberSyntaxError{}
}
caneof = false
cansep = false
cansgn = true
sawexp = true
case c == '-':
if !cansgn {
return Decimal{}, parseNumberSyntaxError{}
}
caneof = false
cansep = false
cansgn = false
eneg = true
case c == '_':
if !cansep {
return Decimal{}, parseNumberSyntaxError{}
}
caneof = false
cansep = false
cansgn = false
case c == '+':
if !cansgn {
return Decimal{}, parseNumberSyntaxError{}
}
caneof = false
cansep = false
cansgn = false
default:
return Decimal{}, parseNumberSyntaxError{}
}
}
if !caneof {
return Decimal{}, parseNumberSyntaxError{}
}
// If the exponent value is larger than the maximum supported exponent,
// there are two cases where the value is still valid:
// - the exponent is negative, where the logical value rounds to 0
// - the significand is zero, where the logical value is 0
//
// Otherwise, return a range error.
if maxexp {
if eneg {
return zero(neg), nil
}
if sig == (uint128{}) {
return zero(neg), nil
}
return inf(neg), parseNumberRangeError{}
}
if eneg {
exp *= -1
}
exp -= nfrac
if exp > maxUnbiasedExponent+39 {
return inf(neg), parseNumberRangeError{}
}
if exp < minUnbiasedExponent-39 {
return zero(neg), nil
}
sig, exp = DefaultRoundingMode.reduce128(neg, sig, exp+exponentBias, trunc)
if exp > maxBiasedExponent {
return inf(neg), parseNumberRangeError{}
}
return compose(neg, sig, exp), nil
}
type parseNumberRangeError struct{}
func (err parseNumberRangeError) Error() string {
return "value out of range"
}
type parseNumberSyntaxError struct{}
func (err parseNumberSyntaxError) Error() string {
return "invalid syntax"
}
type parseRangeError struct {
s string
}
func (err *parseRangeError) Error() string {
return "parsing " + strconv.Quote(err.s) + ": value out of range"
}
func (err *parseRangeError) Is(target error) bool {
return target == strconv.ErrRange
}
type parseSyntaxError struct {
s string
}
func (err *parseSyntaxError) Error() string {
return "parsing " + strconv.Quote(err.s) + ": invalid syntax"
}
func (err *parseSyntaxError) Is(target error) bool {
return target == strconv.ErrSyntax
}