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atoi.go
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atoi.go
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// Copyright 2009 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.
package strconv
import "errors"
// ErrRange indicates that a value is out of range for the target type.
var ErrRange = errors.New("value out of range")
// ErrSyntax indicates that a value does not have the right syntax for the target type.
var ErrSyntax = errors.New("invalid syntax")
// A NumError records a failed conversion.
type NumError struct {
Func string // the failing function (ParseBool, ParseInt, ParseUint, ParseFloat)
Num string // the input
Err error // the reason the conversion failed (e.g. ErrRange, ErrSyntax, etc.)
}
func (e *NumError) Error() string {
return "strconv." + e.Func + ": " + "parsing " + Quote(e.Num) + ": " + e.Err.Error()
}
func syntaxError(fn, str string) *NumError {
return &NumError{fn, str, ErrSyntax}
}
func rangeError(fn, str string) *NumError {
return &NumError{fn, str, ErrRange}
}
func baseError(fn, str string, base int) *NumError {
return &NumError{fn, str, errors.New("invalid base " + Itoa(base))}
}
func bitSizeError(fn, str string, bitSize int) *NumError {
return &NumError{fn, str, errors.New("invalid bit size " + Itoa(bitSize))}
}
const intSize = 32 << (^uint(0) >> 63)
// IntSize is the size in bits of an int or uint value.
const IntSize = intSize
const maxUint64 = (1<<64 - 1)
// ParseUint is like ParseInt but for unsigned numbers.
func ParseUint(s string, base int, bitSize int) (uint64, error) {
const fnParseUint = "ParseUint"
if len(s) == 0 {
return 0, syntaxError(fnParseUint, s)
}
s0 := s
switch {
case 2 <= base && base <= 36:
// valid base; nothing to do
case base == 0:
// Look for octal, hex prefix.
switch {
case s[0] == '0' && len(s) > 1 && (s[1] == 'x' || s[1] == 'X'):
if len(s) < 3 {
return 0, syntaxError(fnParseUint, s0)
}
base = 16
s = s[2:]
case s[0] == '0':
base = 8
s = s[1:]
default:
base = 10
}
default:
return 0, baseError(fnParseUint, s0, base)
}
if bitSize == 0 {
bitSize = int(IntSize)
} else if bitSize < 0 || bitSize > 64 {
return 0, bitSizeError(fnParseUint, s0, bitSize)
}
// Cutoff is the smallest number such that cutoff*base > maxUint64.
// Use compile-time constants for common cases.
var cutoff uint64
switch base {
case 10:
cutoff = maxUint64/10 + 1
case 16:
cutoff = maxUint64/16 + 1
default:
cutoff = maxUint64/uint64(base) + 1
}
maxVal := uint64(1)<<uint(bitSize) - 1
var n uint64
for _, c := range []byte(s) {
var d byte
switch {
case '0' <= c && c <= '9':
d = c - '0'
case 'a' <= c && c <= 'z':
d = c - 'a' + 10
case 'A' <= c && c <= 'Z':
d = c - 'A' + 10
default:
return 0, syntaxError(fnParseUint, s0)
}
if d >= byte(base) {
return 0, syntaxError(fnParseUint, s0)
}
if n >= cutoff {
// n*base overflows
return maxVal, rangeError(fnParseUint, s0)
}
n *= uint64(base)
n1 := n + uint64(d)
if n1 < n || n1 > maxVal {
// n+v overflows
return maxVal, rangeError(fnParseUint, s0)
}
n = n1
}
return n, nil
}
// ParseInt interprets a string s in the given base (0, 2 to 36) and
// bit size (0 to 64) and returns the corresponding value i.
//
// If base == 0, the base is implied by the string's prefix:
// base 16 for "0x", base 8 for "0", and base 10 otherwise.
// For bases 1, below 0 or above 36 an error is returned.
//
// The bitSize argument specifies the integer type
// that the result must fit into. Bit sizes 0, 8, 16, 32, and 64
// correspond to int, int8, int16, int32, and int64.
// For a bitSize below 0 or above 64 an error is returned.
//
// The errors that ParseInt returns have concrete type *NumError
// and include err.Num = s. If s is empty or contains invalid
// digits, err.Err = ErrSyntax and the returned value is 0;
// if the value corresponding to s cannot be represented by a
// signed integer of the given size, err.Err = ErrRange and the
// returned value is the maximum magnitude integer of the
// appropriate bitSize and sign.
func ParseInt(s string, base int, bitSize int) (i int64, err error) {
const fnParseInt = "ParseInt"
// Empty string bad.
if len(s) == 0 {
return 0, syntaxError(fnParseInt, s)
}
// Pick off leading sign.
s0 := s
neg := false
if s[0] == '+' {
s = s[1:]
} else if s[0] == '-' {
neg = true
s = s[1:]
}
// Convert unsigned and check range.
var un uint64
un, err = ParseUint(s, base, bitSize)
if err != nil && err.(*NumError).Err != ErrRange {
err.(*NumError).Func = fnParseInt
err.(*NumError).Num = s0
return 0, err
}
if bitSize == 0 {
bitSize = int(IntSize)
}
cutoff := uint64(1 << uint(bitSize-1))
if !neg && un >= cutoff {
return int64(cutoff - 1), rangeError(fnParseInt, s0)
}
if neg && un > cutoff {
return -int64(cutoff), rangeError(fnParseInt, s0)
}
n := int64(un)
if neg {
n = -n
}
return n, nil
}
// Atoi returns the result of ParseInt(s, 10, 0) converted to type int.
func Atoi(s string) (int, error) {
const fnAtoi = "Atoi"
sLen := len(s)
if intSize == 32 && (0 < sLen && sLen < 10) ||
intSize == 64 && (0 < sLen && sLen < 19) {
// Fast path for small integers that fit int type.
s0 := s
if s[0] == '-' || s[0] == '+' {
s = s[1:]
if len(s) < 1 {
return 0, &NumError{fnAtoi, s0, ErrSyntax}
}
}
n := 0
for _, ch := range []byte(s) {
ch -= '0'
if ch > 9 {
return 0, &NumError{fnAtoi, s0, ErrSyntax}
}
n = n*10 + int(ch)
}
if s0[0] == '-' {
n = -n
}
return n, nil
}
// Slow path for invalid or big integers.
i64, err := ParseInt(s, 10, 0)
if nerr, ok := err.(*NumError); ok {
nerr.Func = fnAtoi
}
return int(i64), err
}