# Source file src/math/big/intconv.go

```     1  // Copyright 2015 The Go Authors. All rights reserved.
2  // Use of this source code is governed by a BSD-style
4
5  // This file implements int-to-string conversion functions.
6
7  package big
8
9  import (
10  	"errors"
11  	"fmt"
12  	"io"
13  )
14
15  // Text returns the string representation of x in the given base.
16  // Base must be between 2 and 62, inclusive. The result uses the
17  // lower-case letters 'a' to 'z' for digit values 10 to 35, and
18  // the upper-case letters 'A' to 'Z' for digit values 36 to 61.
19  // No prefix (such as "0x") is added to the string. If x is a nil
20  // pointer it returns "<nil>".
21  func (x *Int) Text(base int) string {
22  	if x == nil {
23  		return "<nil>"
24  	}
25  	return string(x.abs.itoa(x.neg, base))
26  }
27
28  // Append appends the string representation of x, as generated by
29  // x.Text(base), to buf and returns the extended buffer.
30  func (x *Int) Append(buf []byte, base int) []byte {
31  	if x == nil {
32  		return append(buf, "<nil>"...)
33  	}
34  	return append(buf, x.abs.itoa(x.neg, base)...)
35  }
36
37  // String returns the decimal representation of x as generated by
38  // x.Text(10).
39  func (x *Int) String() string {
40  	return x.Text(10)
41  }
42
43  // write count copies of text to s.
44  func writeMultiple(s fmt.State, text string, count int) {
45  	if len(text) > 0 {
46  		b := []byte(text)
47  		for ; count > 0; count-- {
48  			s.Write(b)
49  		}
50  	}
51  }
52
53  var _ fmt.Formatter = intOne // *Int must implement fmt.Formatter
54
55  // Format implements [fmt.Formatter]. It accepts the formats
56  // 'b' (binary), 'o' (octal with 0 prefix), 'O' (octal with 0o prefix),
57  // 'd' (decimal), 'x' (lowercase hexadecimal), and
59  // Also supported are the full suite of package fmt's format
60  // flags for integral types, including '+' and ' ' for sign
61  // control, '#' for leading zero in octal and for hexadecimal,
62  // a leading "0x" or "0X" for "%#x" and "%#X" respectively,
63  // specification of minimum digits precision, output field
64  // width, space or zero padding, and '-' for left or right
65  // justification.
66  func (x *Int) Format(s fmt.State, ch rune) {
67  	// determine base
68  	var base int
69  	switch ch {
70  	case 'b':
71  		base = 2
72  	case 'o', 'O':
73  		base = 8
74  	case 'd', 's', 'v':
75  		base = 10
76  	case 'x', 'X':
77  		base = 16
78  	default:
79  		// unknown format
80  		fmt.Fprintf(s, "%%!%c(big.Int=%s)", ch, x.String())
81  		return
82  	}
83
84  	if x == nil {
85  		fmt.Fprint(s, "<nil>")
86  		return
87  	}
88
89  	// determine sign character
90  	sign := ""
91  	switch {
92  	case x.neg:
93  		sign = "-"
94  	case s.Flag('+'): // supersedes ' ' when both specified
95  		sign = "+"
96  	case s.Flag(' '):
97  		sign = " "
98  	}
99
100  	// determine prefix characters for indicating output base
101  	prefix := ""
102  	if s.Flag('#') {
103  		switch ch {
104  		case 'b': // binary
105  			prefix = "0b"
106  		case 'o': // octal
107  			prefix = "0"
109  			prefix = "0x"
110  		case 'X':
111  			prefix = "0X"
112  		}
113  	}
114  	if ch == 'O' {
115  		prefix = "0o"
116  	}
117
118  	digits := x.abs.utoa(base)
119  	if ch == 'X' {
120  		// faster than bytes.ToUpper
121  		for i, d := range digits {
122  			if 'a' <= d && d <= 'z' {
123  				digits[i] = 'A' + (d - 'a')
124  			}
125  		}
126  	}
127
128  	// number of characters for the three classes of number padding
129  	var left int  // space characters to left of digits for right justification ("%8d")
130  	var zeros int // zero characters (actually cs[0]) as left-most digits ("%.8d")
131  	var right int // space characters to right of digits for left justification ("%-8d")
132
133  	// determine number padding from precision: the least number of digits to output
134  	precision, precisionSet := s.Precision()
135  	if precisionSet {
136  		switch {
137  		case len(digits) < precision:
138  			zeros = precision - len(digits) // count of zero padding
139  		case len(digits) == 1 && digits[0] == '0' && precision == 0:
140  			return // print nothing if zero value (x == 0) and zero precision ("." or ".0")
141  		}
142  	}
143
144  	// determine field pad from width: the least number of characters to output
145  	length := len(sign) + len(prefix) + zeros + len(digits)
146  	if width, widthSet := s.Width(); widthSet && length < width { // pad as specified
147  		switch d := width - length; {
148  		case s.Flag('-'):
149  			// pad on the right with spaces; supersedes '0' when both specified
150  			right = d
151  		case s.Flag('0') && !precisionSet:
152  			// pad with zeros unless precision also specified
153  			zeros = d
154  		default:
155  			// pad on the left with spaces
156  			left = d
157  		}
158  	}
159
161  	writeMultiple(s, " ", left)
162  	writeMultiple(s, sign, 1)
163  	writeMultiple(s, prefix, 1)
164  	writeMultiple(s, "0", zeros)
165  	s.Write(digits)
166  	writeMultiple(s, " ", right)
167  }
168
169  // scan sets z to the integer value corresponding to the longest possible prefix
170  // read from r representing a signed integer number in a given conversion base.
171  // It returns z, the actual conversion base used, and an error, if any. In the
172  // error case, the value of z is undefined but the returned value is nil. The
173  // syntax follows the syntax of integer literals in Go.
174  //
175  // The base argument must be 0 or a value from 2 through MaxBase. If the base
176  // is 0, the string prefix determines the actual conversion base. A prefix of
177  // “0b” or “0B” selects base 2; a “0”, “0o”, or “0O” prefix selects
178  // base 8, and a “0x” or “0X” prefix selects base 16. Otherwise the selected
179  // base is 10.
180  func (z *Int) scan(r io.ByteScanner, base int) (*Int, int, error) {
181  	// determine sign
182  	neg, err := scanSign(r)
183  	if err != nil {
184  		return nil, 0, err
185  	}
186
187  	// determine mantissa
188  	z.abs, base, _, err = z.abs.scan(r, base, false)
189  	if err != nil {
190  		return nil, base, err
191  	}
192  	z.neg = len(z.abs) > 0 && neg // 0 has no sign
193
194  	return z, base, nil
195  }
196
197  func scanSign(r io.ByteScanner) (neg bool, err error) {
198  	var ch byte
199  	if ch, err = r.ReadByte(); err != nil {
200  		return false, err
201  	}
202  	switch ch {
203  	case '-':
204  		neg = true
205  	case '+':
206  		// nothing to do
207  	default:
209  	}
210  	return
211  }
212
213  // byteReader is a local wrapper around fmt.ScanState;
214  // it implements the ByteReader interface.
216  	fmt.ScanState
217  }
218
220  	ch, size, err := r.ReadRune()
221  	if size != 1 && err == nil {
222  		err = fmt.Errorf("invalid rune %#U", ch)
223  	}
224  	return byte(ch), err
225  }
226
229  }
230
231  var _ fmt.Scanner = intOne // *Int must implement fmt.Scanner
232
233  // Scan is a support routine for [fmt.Scanner]; it sets z to the value of
234  // the scanned number. It accepts the formats 'b' (binary), 'o' (octal),
236  func (z *Int) Scan(s fmt.ScanState, ch rune) error {
237  	s.SkipSpace() // skip leading space characters
238  	base := 0
239  	switch ch {
240  	case 'b':
241  		base = 2
242  	case 'o':
243  		base = 8
244  	case 'd':
245  		base = 10
246  	case 'x', 'X':
247  		base = 16
248  	case 's', 'v':
249  		// let scan determine the base
250  	default:
251  		return errors.New("Int.Scan: invalid verb")
252  	}
253  	_, _, err := z.scan(byteReader{s}, base)
254  	return err
255  }
256
```

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