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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 (ErrRange, ErrSyntax)
}

func (e *NumError) Error() string {
        return "strconv." + e.Func + ": " + `parsing "` + 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}
}

const intSize = 32 << uint(^uint(0)>>63)

const IntSize = intSize // number of bits in int, uint (32 or 64)

// Return the first number n such that n*base >= 1<<64.
func cutoff64(base int) uint64 {
        if base < 2 {
                return 0
        }
        return (1<<64-1)/uint64(base) + 1
}

// ParseUint is like ParseInt but for unsigned numbers.
func ParseUint(s string, b int, bitSize int) (n uint64, err error) {
        var cutoff, maxVal uint64

        if bitSize == 0 {
                bitSize = int(IntSize)
        }

        s0 := s
        switch {
        case len(s) < 1:
                err = ErrSyntax
                goto Error

        case 2 <= b && b <= 36:
                // valid base; nothing to do

        case b == 0:
                // Look for octal, hex prefix.
                switch {
                case s[0] == '0' && len(s) > 1 && (s[1] == 'x' || s[1] == 'X'):
                        b = 16
                        s = s[2:]
                        if len(s) < 1 {
                                err = ErrSyntax
                                goto Error
                        }
                case s[0] == '0':
                        b = 8
                default:
                        b = 10
                }

        default:
                err = errors.New("invalid base " + Itoa(b))
                goto Error
        }

        n = 0
        cutoff = cutoff64(b)
        maxVal = 1<<uint(bitSize) - 1

        for i := 0; i < len(s); i++ {
                var v byte
                d := s[i]
                switch {
                case '0' <= d && d <= '9':
                        v = d - '0'
                case 'a' <= d && d <= 'z':
                        v = d - 'a' + 10
                case 'A' <= d && d <= 'Z':
                        v = d - 'A' + 10
                default:
                        n = 0
                        err = ErrSyntax
                        goto Error
                }
                if int(v) >= b {
                        n = 0
                        err = ErrSyntax
                        goto Error
                }

                if n >= cutoff {
                        // n*b overflows
                        n = 1<<64 - 1
                        err = ErrRange
                        goto Error
                }
                n *= uint64(b)

                n1 := n + uint64(v)
                if n1 < n || n1 > maxVal {
                        // n+v overflows
                        n = 1<<64 - 1
                        err = ErrRange
                        goto Error
                }
                n = n1
        }

        return n, nil

Error:
        return n, &NumError{"ParseUint", s0, err}
}

// ParseInt interprets a string s in the given base (2 to 36) 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.
//
// 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.
//
// The errors that ParseInt returns have concrete type *NumError
// and include err.Num = s.  If s is empty or contains invalid
// digits, err.Error = ErrSyntax; if the value corresponding
// to s cannot be represented by a signed integer of the
// given size, err.Error = ErrRange.
func ParseInt(s string, base int, bitSize int) (i int64, err error) {
        const fnParseInt = "ParseInt"

        if bitSize == 0 {
                bitSize = int(IntSize)
        }

        // 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
        }
        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 is shorthand for ParseInt(s, 10, 0).
func Atoi(s string) (i int, err error) {
        i64, err := ParseInt(s, 10, 0)
        return int(i64), err
}