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// Copyright 2015 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.
// This file implements int-to-string conversion functions.
package big
import (
"errors"
"fmt"
"io"
)
// TODO(gri) Should rename itoa to utoa (there's no sign). That
// would permit the introduction of itoa which is like utoa but
// reserves a byte for a possible sign that's passed in. That
// would permit Int.Text to be implemented w/o the need for
// string copy if the number is negative.
// Text returns the string representation of x in the given base.
// Base must be between 2 and 36, inclusive. The result uses the
// lower-case letters 'a' to 'z' for digit values >= 10. No base
// prefix (such as "0x") is added to the string.
func (x *Int) Text(base int) string {
if x == nil {
return "<nil>"
}
return string(x.abs.itoa(x.neg, base))
}
// Append appends the string representation of x, as generated by
// x.Text(base), to buf and returns the extended buffer.
func (x *Int) Append(buf []byte, base int) []byte {
if x == nil {
return append(buf, "<nil>"...)
}
return append(buf, x.abs.itoa(x.neg, base)...)
}
func (x *Int) String() string {
return x.Text(10)
}
// write count copies of text to s
func writeMultiple(s fmt.State, text string, count int) {
if len(text) > 0 {
b := []byte(text)
for ; count > 0; count-- {
s.Write(b)
}
}
}
var _ fmt.Formatter = intOne // *Int must implement fmt.Formatter
// Format implements fmt.Formatter. It accepts the formats
// 'b' (binary), 'o' (octal), 'd' (decimal), 'x' (lowercase
// hexadecimal), and 'X' (uppercase hexadecimal).
// Also supported are the full suite of package fmt's format
// flags for integral types, including '+' and ' ' for sign
// control, '#' for leading zero in octal and for hexadecimal,
// a leading "0x" or "0X" for "%#x" and "%#X" respectively,
// specification of minimum digits precision, output field
// width, space or zero padding, and '-' for left or right
// justification.
//
func (x *Int) Format(s fmt.State, ch rune) {
// determine base
var base int
switch ch {
case 'b':
base = 2
case 'o':
base = 8
case 'd', 's', 'v':
base = 10
case 'x', 'X':
base = 16
default:
// unknown format
fmt.Fprintf(s, "%%!%c(big.Int=%s)", ch, x.String())
return
}
if x == nil {
fmt.Fprint(s, "<nil>")
return
}
// determine sign character
sign := ""
switch {
case x.neg:
sign = "-"
case s.Flag('+'): // supersedes ' ' when both specified
sign = "+"
case s.Flag(' '):
sign = " "
}
// determine prefix characters for indicating output base
prefix := ""
if s.Flag('#') {
switch ch {
case 'o': // octal
prefix = "0"
case 'x': // hexadecimal
prefix = "0x"
case 'X':
prefix = "0X"
}
}
digits := x.abs.utoa(base)
if ch == 'X' {
// faster than bytes.ToUpper
for i, d := range digits {
if 'a' <= d && d <= 'z' {
digits[i] = 'A' + (d - 'a')
}
}
}
// number of characters for the three classes of number padding
var left int // space characters to left of digits for right justification ("%8d")
var zeros int // zero characters (actually cs[0]) as left-most digits ("%.8d")
var right int // space characters to right of digits for left justification ("%-8d")
// determine number padding from precision: the least number of digits to output
precision, precisionSet := s.Precision()
if precisionSet {
switch {
case len(digits) < precision:
zeros = precision - len(digits) // count of zero padding
case len(digits) == 1 && digits[0] == '0' && precision == 0:
return // print nothing if zero value (x == 0) and zero precision ("." or ".0")
}
}
// determine field pad from width: the least number of characters to output
length := len(sign) + len(prefix) + zeros + len(digits)
if width, widthSet := s.Width(); widthSet && length < width { // pad as specified
switch d := width - length; {
case s.Flag('-'):
// pad on the right with spaces; supersedes '0' when both specified
right = d
case s.Flag('0') && !precisionSet:
// pad with zeros unless precision also specified
zeros = d
default:
// pad on the left with spaces
left = d
}
}
// print number as [left pad][sign][prefix][zero pad][digits][right pad]
writeMultiple(s, " ", left)
writeMultiple(s, sign, 1)
writeMultiple(s, prefix, 1)
writeMultiple(s, "0", zeros)
s.Write(digits)
writeMultiple(s, " ", right)
}
// scan sets z to the integer value corresponding to the longest possible prefix
// read from r representing a signed integer number in a given conversion base.
// It returns z, the actual conversion base used, and an error, if any. In the
// error case, the value of z is undefined but the returned value is nil. The
// syntax follows the syntax of integer literals in Go.
//
// The base argument must be 0 or a value from 2 through MaxBase. If the base
// is 0, the string prefix determines the actual conversion base. A prefix of
// ``0x'' or ``0X'' selects base 16; the ``0'' prefix selects base 8, and a
// ``0b'' or ``0B'' prefix selects base 2. Otherwise the selected base is 10.
//
func (z *Int) scan(r io.ByteScanner, base int) (*Int, int, error) {
// determine sign
neg, err := scanSign(r)
if err != nil {
return nil, 0, err
}
// determine mantissa
z.abs, base, _, err = z.abs.scan(r, base, false)
if err != nil {
return nil, base, err
}
z.neg = len(z.abs) > 0 && neg // 0 has no sign
return z, base, nil
}
func scanSign(r io.ByteScanner) (neg bool, err error) {
var ch byte
if ch, err = r.ReadByte(); err != nil {
return false, err
}
switch ch {
case '-':
neg = true
case '+':
// nothing to do
default:
r.UnreadByte()
}
return
}
// byteReader is a local wrapper around fmt.ScanState;
// it implements the ByteReader interface.
type byteReader struct {
fmt.ScanState
}
func (r byteReader) ReadByte() (byte, error) {
ch, size, err := r.ReadRune()
if size != 1 && err == nil {
err = fmt.Errorf("invalid rune %#U", ch)
}
return byte(ch), err
}
func (r byteReader) UnreadByte() error {
return r.UnreadRune()
}
var _ fmt.Scanner = intOne // *Int must implement fmt.Scanner
// Scan is a support routine for fmt.Scanner; it sets z to the value of
// the scanned number. It accepts the formats 'b' (binary), 'o' (octal),
// 'd' (decimal), 'x' (lowercase hexadecimal), and 'X' (uppercase hexadecimal).
func (z *Int) Scan(s fmt.ScanState, ch rune) error {
s.SkipSpace() // skip leading space characters
base := 0
switch ch {
case 'b':
base = 2
case 'o':
base = 8
case 'd':
base = 10
case 'x', 'X':
base = 16
case 's', 'v':
// let scan determine the base
default:
return errors.New("Int.Scan: invalid verb")
}
_, _, err := z.scan(byteReader{s}, base)
return err
}