Source: intconv.go in package math/big

This file implements int-to-string conversion functions.


package big

import (
	"errors"
	"fmt"
	"io"
)

Text returns the string representation of x in the given base. Base must be between 2 and 62, inclusive. The result uses the lower-case letters 'a' to 'z' for digit values 10 to 35, and the upper-case letters 'A' to 'Z' for digit values 36 to 61. No prefix (such as "0x") is added to the string. If x is a nil pointer it returns "<nil>".

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)...)
}

String returns the decimal representation of x as generated by x.Text(10).

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 with 0 prefix), 'O' (octal with 0o prefix), '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.

determine base

	var base int
	switch ch {
	case 'b':
		base = 2
	case 'o', 'O':
		base = 8
	case 'd', 's', 'v':
		base = 10
	case 'x', 'X':
		base = 16

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 'b': // binary
			prefix = "0b"
		case 'o': // octal
			prefix = "0"
		case 'x': // hexadecimal
			prefix = "0x"
		case 'X':
			prefix = "0X"
		}
	}
	if ch == 'O' {
		prefix = "0o"
	}

	digits := x.abs.utoa(base)

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; {

pad on the right with spaces; supersedes '0' when both specified

			right = d

pad with zeros unless precision also specified

			zeros = d

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 ``0b'' or ``0B'' selects base 2; a ``0'', ``0o'', or ``0O'' prefix selects base 8, and a ``0x'' or ``0X'' prefix selects base 16. Otherwise the selected base is 10.

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

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

let scan determine the base

	default:
		return errors.New("Int.Scan: invalid verb")
	}
	_, _, err := z.scan(byteReader{s}, base)
	return err