src/fmt/format.go - go - Git at Google

 // 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 fmt

 import (
 	"strconv"
 	"unicode/utf8"
 )

 const (
 	ldigits = "0123456789abcdefx"
 	udigits = "0123456789ABCDEFX"
 )

 const (
 	signed   = true
 	unsigned = false
 )

 // flags placed in a separate struct for easy clearing.
 type fmtFlags struct {
 	widPresent  bool
 	precPresent bool
 	minus       bool
 	plus        bool
 	sharp       bool
 	space       bool
 	zero        bool

 	// For the formats %+v %#v, we set the plusV/sharpV flags
 	// and clear the plus/sharp flags since %+v and %#v are in effect
 	// different, flagless formats set at the top level.
 	plusV  bool
 	sharpV bool
 }

 // A fmt is the raw formatter used by Printf etc.
 // It prints into a buffer that must be set up separately.
 type fmt struct {
 	buf *buffer

 	fmtFlags

 	wid  int // width
 	prec int // precision

 	// intbuf is large enough to store %b of an int64 with a sign and
 	// avoids padding at the end of the struct on 32 bit architectures.
 	intbuf [68]byte
 }

 func (f *fmt) clearflags() {
 	f.fmtFlags = fmtFlags{}
 }

 func (f *fmt) init(buf *buffer) {
 	f.buf = buf
 	f.clearflags()
 }

 // writePadding generates n bytes of padding.
 func (f *fmt) writePadding(n int) {
 	if n <= 0 { // No padding bytes needed.
 		return
 	}
 	buf := *f.buf
 	oldLen := len(buf)
 	newLen := oldLen + n
 	// Make enough room for padding.
 	if newLen > cap(buf) {
 		buf = make(buffer, cap(buf)*2+n)
 		copy(buf, *f.buf)
 	}
 	// Decide which byte the padding should be filled with.
 	padByte := byte(' ')
 	if f.zero {
 		padByte = byte('0')
 	}
 	// Fill padding with padByte.
 	padding := buf[oldLen:newLen]
 	for i := range padding {
 		padding[i] = padByte
 	}
 	*f.buf = buf[:newLen]
 }

 // pad appends b to f.buf, padded on left (!f.minus) or right (f.minus).
 func (f *fmt) pad(b []byte) {
 	if !f.widPresent || f.wid == 0 {
 		f.buf.write(b)
 		return
 	}
 	width := f.wid - utf8.RuneCount(b)
 	if !f.minus {
 		// left padding
 		f.writePadding(width)
 		f.buf.write(b)
 	} else {
 		// right padding
 		f.buf.write(b)
 		f.writePadding(width)
 	}
 }

 // padString appends s to f.buf, padded on left (!f.minus) or right (f.minus).
 func (f *fmt) padString(s string) {
 	if !f.widPresent || f.wid == 0 {
 		f.buf.writeString(s)
 		return
 	}
 	width := f.wid - utf8.RuneCountInString(s)
 	if !f.minus {
 		// left padding
 		f.writePadding(width)
 		f.buf.writeString(s)
 	} else {
 		// right padding
 		f.buf.writeString(s)
 		f.writePadding(width)
 	}
 }

 // fmtBoolean formats a boolean.
 func (f *fmt) fmtBoolean(v bool) {
 	if v {
 		f.padString("true")
 	} else {
 		f.padString("false")
 	}
 }

 // fmtUnicode formats a uint64 as "U+0078" or with f.sharp set as "U+0078 'x'".
 func (f *fmt) fmtUnicode(u uint64) {
 	buf := f.intbuf[0:]

 	// With default precision set the maximum needed buf length is 18
 	// for formatting -1 with %#U ("U+FFFFFFFFFFFFFFFF") which fits
 	// into the already allocated intbuf with a capacity of 68 bytes.
 	prec := 4
 	if f.precPresent && f.prec > 4 {
 		prec = f.prec
 		// Compute space needed for "U+" , number, " '", character, "'".
 		width := 2 + prec + 2 + utf8.UTFMax + 1
 		if width > len(buf) {
 			buf = make([]byte, width)
 		}
 	}

 	// Format into buf, ending at buf[i]. Formatting numbers is easier right-to-left.
 	i := len(buf)

 	// For %#U we want to add a space and a quoted character at the end of the buffer.
 	if f.sharp && u <= utf8.MaxRune && strconv.IsPrint(rune(u)) {
 		i--
 		buf[i] = '\''
 		i -= utf8.RuneLen(rune(u))
 		utf8.EncodeRune(buf[i:], rune(u))
 		i--
 		buf[i] = '\''
 		i--
 		buf[i] = ' '
 	}
 	// Format the Unicode code point u as a hexadecimal number.
 	for u >= 16 {
 		i--
 		buf[i] = udigits[u&0xF]
 		prec--
 		u >>= 4
 	}
 	i--
 	buf[i] = udigits[u]
 	prec--
 	// Add zeros in front of the number until requested precision is reached.
 	for prec > 0 {
 		i--
 		buf[i] = '0'
 		prec--
 	}
 	// Add a leading "U+".
 	i--
 	buf[i] = '+'
 	i--
 	buf[i] = 'U'

 	oldZero := f.zero
 	f.zero = false
 	f.pad(buf[i:])
 	f.zero = oldZero
 }

 // fmtInteger formats signed and unsigned integers.
 func (f *fmt) fmtInteger(u uint64, base int, isSigned bool, verb rune, digits string) {
 	negative := isSigned && int64(u) < 0
 	if negative {
 		u = -u
 	}

 	buf := f.intbuf[0:]
 	// The already allocated f.intbuf with a capacity of 68 bytes
 	// is large enough for integer formatting when no precision or width is set.
 	if f.widPresent || f.precPresent {
 		// Account 3 extra bytes for possible addition of a sign and "0x".
 		width := 3 + f.wid + f.prec // wid and prec are always positive.
 		if width > len(buf) {
 			// We're going to need a bigger boat.
 			buf = make([]byte, width)
 		}
 	}

 	// Two ways to ask for extra leading zero digits: %.3d or %03d.
 	// If both are specified the f.zero flag is ignored and
 	// padding with spaces is used instead.
 	prec := 0
 	if f.precPresent {
 		prec = f.prec
 		// Precision of 0 and value of 0 means "print nothing" but padding.
 		if prec == 0 && u == 0 {
 			oldZero := f.zero
 			f.zero = false
 			f.writePadding(f.wid)
 			f.zero = oldZero
 			return
 		}
 	} else if f.zero && f.widPresent {
 		prec = f.wid
 		if negative || f.plus || f.space {
 			prec-- // leave room for sign
 		}
 	}

 	// Because printing is easier right-to-left: format u into buf, ending at buf[i].
 	// We could make things marginally faster by splitting the 32-bit case out
 	// into a separate block but it's not worth the duplication, so u has 64 bits.
 	i := len(buf)
 	// Use constants for the division and modulo for more efficient code.
 	// Switch cases ordered by popularity.
 	switch base {
 	case 10:
 		for u >= 10 {
 			i--
 			next := u / 10
 			buf[i] = byte('0' + u - next*10)
 			u = next
 		}
 	case 16:
 		for u >= 16 {
 			i--
 			buf[i] = digits[u&0xF]
 			u >>= 4
 		}
 	case 8:
 		for u >= 8 {
 			i--
 			buf[i] = byte('0' + u&7)
 			u >>= 3
 		}
 	case 2:
 		for u >= 2 {
 			i--
 			buf[i] = byte('0' + u&1)
 			u >>= 1
 		}
 	default:
 		panic("fmt: unknown base; can't happen")
 	}
 	i--
 	buf[i] = digits[u]
 	for i > 0 && prec > len(buf)-i {
 		i--
 		buf[i] = '0'
 	}

 	// Various prefixes: 0x, -, etc.
 	if f.sharp {
 		switch base {
 		case 2:
 			// Add a leading 0b.
 			i--
 			buf[i] = 'b'
 			i--
 			buf[i] = '0'
 		case 8:
 			if buf[i] != '0' {
 				i--
 				buf[i] = '0'
 			}
 		case 16:
 			// Add a leading 0x or 0X.
 			i--
 			buf[i] = digits[16]
 			i--
 			buf[i] = '0'
 		}
 	}
 	if verb == 'O' {
 		i--
 		buf[i] = 'o'
 		i--
 		buf[i] = '0'
 	}

 	if negative {
 		i--
 		buf[i] = '-'
 	} else if f.plus {
 		i--
 		buf[i] = '+'
 	} else if f.space {
 		i--
 		buf[i] = ' '
 	}

 	// Left padding with zeros has already been handled like precision earlier
 	// or the f.zero flag is ignored due to an explicitly set precision.
 	oldZero := f.zero
 	f.zero = false
 	f.pad(buf[i:])
 	f.zero = oldZero
 }

 // truncateString truncates the string s to the specified precision, if present.
 func (f *fmt) truncateString(s string) string {
 	if f.precPresent {
 		n := f.prec
 		for i := range s {
 			n--
 			if n < 0 {
 				return s[:i]
 			}
 		}
 	}
 	return s
 }

 // truncate truncates the byte slice b as a string of the specified precision, if present.
 func (f *fmt) truncate(b []byte) []byte {
 	if f.precPresent {
 		n := f.prec
 		for i := 0; i < len(b); {
 			n--
 			if n < 0 {
 				return b[:i]
 			}
 			wid := 1
 			if b[i] >= utf8.RuneSelf {
 				_, wid = utf8.DecodeRune(b[i:])
 			}
 			i += wid
 		}
 	}
 	return b
 }

 // fmtS formats a string.
 func (f *fmt) fmtS(s string) {
 	s = f.truncateString(s)
 	f.padString(s)
 }

 // fmtBs formats the byte slice b as if it was formatted as string with fmtS.
 func (f *fmt) fmtBs(b []byte) {
 	b = f.truncate(b)
 	f.pad(b)
 }

 // fmtSbx formats a string or byte slice as a hexadecimal encoding of its bytes.
 func (f *fmt) fmtSbx(s string, b []byte, digits string) {
 	length := len(b)
 	if b == nil {
 		// No byte slice present. Assume string s should be encoded.
 		length = len(s)
 	}
 	// Set length to not process more bytes than the precision demands.
 	if f.precPresent && f.prec < length {
 		length = f.prec
 	}
 	// Compute width of the encoding taking into account the f.sharp and f.space flag.
 	width := 2 * length
 	if width > 0 {
 		if f.space {
 			// Each element encoded by two hexadecimals will get a leading 0x or 0X.
 			if f.sharp {
 				width *= 2
 			}
 			// Elements will be separated by a space.
 			width += length - 1
 		} else if f.sharp {
 			// Only a leading 0x or 0X will be added for the whole string.
 			width += 2
 		}
 	} else { // The byte slice or string that should be encoded is empty.
 		if f.widPresent {
 			f.writePadding(f.wid)
 		}
 		return
 	}
 	// Handle padding to the left.
 	if f.widPresent && f.wid > width && !f.minus {
 		f.writePadding(f.wid - width)
 	}
 	// Write the encoding directly into the output buffer.
 	buf := *f.buf
 	if f.sharp {
 		// Add leading 0x or 0X.
 		buf = append(buf, '0', digits[16])
 	}
 	var c byte
 	for i := 0; i < length; i++ {
 		if f.space && i > 0 {
 			// Separate elements with a space.
 			buf = append(buf, ' ')
 			if f.sharp {
 				// Add leading 0x or 0X for each element.
 				buf = append(buf, '0', digits[16])
 			}
 		}
 		if b != nil {
 			c = b[i] // Take a byte from the input byte slice.
 		} else {
 			c = s[i] // Take a byte from the input string.
 		}
 		// Encode each byte as two hexadecimal digits.
 		buf = append(buf, digits[c>>4], digits[c&0xF])
 	}
 	*f.buf = buf
 	// Handle padding to the right.
 	if f.widPresent && f.wid > width && f.minus {
 		f.writePadding(f.wid - width)
 	}
 }

 // fmtSx formats a string as a hexadecimal encoding of its bytes.
 func (f *fmt) fmtSx(s, digits string) {
 	f.fmtSbx(s, nil, digits)
 }

 // fmtBx formats a byte slice as a hexadecimal encoding of its bytes.
 func (f *fmt) fmtBx(b []byte, digits string) {
 	f.fmtSbx("", b, digits)
 }

 // fmtQ formats a string as a double-quoted, escaped Go string constant.
 // If f.sharp is set a raw (backquoted) string may be returned instead
 // if the string does not contain any control characters other than tab.
 func (f *fmt) fmtQ(s string) {
 	s = f.truncateString(s)
 	if f.sharp && strconv.CanBackquote(s) {
 		f.padString("`" + s + "`")
 		return
 	}
 	buf := f.intbuf[:0]
 	if f.plus {
 		f.pad(strconv.AppendQuoteToASCII(buf, s))
 	} else {
 		f.pad(strconv.AppendQuote(buf, s))
 	}
 }

 // fmtC formats an integer as a Unicode character.
 // If the character is not valid Unicode, it will print '\ufffd'.
 func (f *fmt) fmtC(c uint64) {
 	// Explicitly check whether c exceeds utf8.MaxRune since the conversion
 	// of a uint64 to a rune may lose precision that indicates an overflow.
 	r := rune(c)
 	if c > utf8.MaxRune {
 		r = utf8.RuneError
 	}
 	buf := f.intbuf[:0]
 	f.pad(utf8.AppendRune(buf, r))
 }

 // fmtQc formats an integer as a single-quoted, escaped Go character constant.
 // If the character is not valid Unicode, it will print '\ufffd'.
 func (f *fmt) fmtQc(c uint64) {
 	r := rune(c)
 	if c > utf8.MaxRune {
 		r = utf8.RuneError
 	}
 	buf := f.intbuf[:0]
 	if f.plus {
 		f.pad(strconv.AppendQuoteRuneToASCII(buf, r))
 	} else {
 		f.pad(strconv.AppendQuoteRune(buf, r))
 	}
 }

 // fmtFloat formats a float64. It assumes that verb is a valid format specifier
 // for strconv.AppendFloat and therefore fits into a byte.
 func (f *fmt) fmtFloat(v float64, size int, verb rune, prec int) {
 	// Explicit precision in format specifier overrules default precision.
 	if f.precPresent {
 		prec = f.prec
 	}
 	// Format number, reserving space for leading + sign if needed.
 	num := strconv.AppendFloat(f.intbuf[:1], v, byte(verb), prec, size)
 	if num[1] == '-' || num[1] == '+' {
 		num = num[1:]
 	} else {
 		num[0] = '+'
 	}
 	// f.space means to add a leading space instead of a "+" sign unless
 	// the sign is explicitly asked for by f.plus.
 	if f.space && num[0] == '+' && !f.plus {
 		num[0] = ' '
 	}
 	// Special handling for infinities and NaN,
 	// which don't look like a number so shouldn't be padded with zeros.
 	if num[1] == 'I' || num[1] == 'N' {
 		oldZero := f.zero
 		f.zero = false
 		// Remove sign before NaN if not asked for.
 		if num[1] == 'N' && !f.space && !f.plus {
 			num = num[1:]
 		}
 		f.pad(num)
 		f.zero = oldZero
 		return
 	}
 	// The sharp flag forces printing a decimal point for non-binary formats
 	// and retains trailing zeros, which we may need to restore.
 	if f.sharp && verb != 'b' {
 		digits := 0
 		switch verb {
 		case 'v', 'g', 'G', 'x':
 			digits = prec
 			// If no precision is set explicitly use a precision of 6.
 			if digits == -1 {
 				digits = 6
 			}
 		}

 		// Buffer pre-allocated with enough room for
 		// exponent notations of the form "e+123" or "p-1023".
 		var tailBuf [6]byte
 		tail := tailBuf[:0]

 		hasDecimalPoint := false
 		sawNonzeroDigit := false
 		// Starting from i = 1 to skip sign at num[0].
 		for i := 1; i < len(num); i++ {
 			switch num[i] {
 			case '.':
 				hasDecimalPoint = true
 			case 'p', 'P':
 				tail = append(tail, num[i:]...)
 				num = num[:i]
 			case 'e', 'E':
 				if verb != 'x' && verb != 'X' {
 					tail = append(tail, num[i:]...)
 					num = num[:i]
 					break
 				}
 				fallthrough
 			default:
 				if num[i] != '0' {
 					sawNonzeroDigit = true
 				}
 				// Count significant digits after the first non-zero digit.
 				if sawNonzeroDigit {
 					digits--
 				}
 			}
 		}
 		if !hasDecimalPoint {
 			// Leading digit 0 should contribute once to digits.
 			if len(num) == 2 && num[1] == '0' {
 				digits--
 			}
 			num = append(num, '.')
 		}
 		for digits > 0 {
 			num = append(num, '0')
 			digits--
 		}
 		num = append(num, tail...)
 	}
 	// We want a sign if asked for and if the sign is not positive.
 	if f.plus || num[0] != '+' {
 		// If we're zero padding to the left we want the sign before the leading zeros.
 		// Achieve this by writing the sign out and then padding the unsigned number.
 		if f.zero && f.widPresent && f.wid > len(num) {
 			f.buf.writeByte(num[0])
 			f.writePadding(f.wid - len(num))
 			f.buf.write(num[1:])
 			return
 		}
 		f.pad(num)
 		return
 	}
 	// No sign to show and the number is positive; just print the unsigned number.
 	f.pad(num[1:])
 }
	// 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 fmt

	import (
	"strconv"
	"unicode/utf8"
	)

	const (
	ldigits = "0123456789abcdefx"
	udigits = "0123456789ABCDEFX"
	)

	const (
	signed = true
	unsigned = false
	)

	// flags placed in a separate struct for easy clearing.
	type fmtFlags struct {
	widPresent bool
	precPresent bool
	minus bool
	plus bool
	sharp bool
	space bool
	zero bool

	// For the formats %+v %#v, we set the plusV/sharpV flags
	// and clear the plus/sharp flags since %+v and %#v are in effect
	// different, flagless formats set at the top level.
	plusV bool
	sharpV bool
	}

	// A fmt is the raw formatter used by Printf etc.
	// It prints into a buffer that must be set up separately.
	type fmt struct {
	buf *buffer

	fmtFlags

	wid int // width
	prec int // precision

	// intbuf is large enough to store %b of an int64 with a sign and
	// avoids padding at the end of the struct on 32 bit architectures.
	intbuf [68]byte
	}

	func (f *fmt) clearflags() {
	f.fmtFlags = fmtFlags{}
	}

	func (f fmt) init(buf buffer) {
	f.buf = buf
	f.clearflags()
	}

	// writePadding generates n bytes of padding.
	func (f *fmt) writePadding(n int) {
	if n <= 0 { // No padding bytes needed.
	return
	}
	buf := *f.buf
	oldLen := len(buf)
	newLen := oldLen + n
	// Make enough room for padding.
	if newLen > cap(buf) {
	buf = make(buffer, cap(buf)*2+n)
	copy(buf, *f.buf)
	}
	// Decide which byte the padding should be filled with.
	padByte := byte(' ')
	if f.zero {
	padByte = byte('0')
	}
	// Fill padding with padByte.
	padding := buf[oldLen:newLen]
	for i := range padding {
	padding[i] = padByte
	}
	*f.buf = buf[:newLen]
	}

	// pad appends b to f.buf, padded on left (!f.minus) or right (f.minus).
	func (f *fmt) pad(b []byte) {
	if !f.widPresent \|\| f.wid == 0 {
	f.buf.write(b)
	return
	}
	width := f.wid - utf8.RuneCount(b)
	if !f.minus {
	// left padding
	f.writePadding(width)
	f.buf.write(b)
	} else {
	// right padding
	f.buf.write(b)
	f.writePadding(width)
	}
	}

	// padString appends s to f.buf, padded on left (!f.minus) or right (f.minus).
	func (f *fmt) padString(s string) {
	if !f.widPresent \|\| f.wid == 0 {
	f.buf.writeString(s)
	return
	}
	width := f.wid - utf8.RuneCountInString(s)
	if !f.minus {
	// left padding
	f.writePadding(width)
	f.buf.writeString(s)
	} else {
	// right padding
	f.buf.writeString(s)
	f.writePadding(width)
	}
	}

	// fmtBoolean formats a boolean.
	func (f *fmt) fmtBoolean(v bool) {
	if v {
	f.padString("true")
	} else {
	f.padString("false")
	}
	}

	// fmtUnicode formats a uint64 as "U+0078" or with f.sharp set as "U+0078 'x'".
	func (f *fmt) fmtUnicode(u uint64) {
	buf := f.intbuf[0:]

	// With default precision set the maximum needed buf length is 18
	// for formatting -1 with %#U ("U+FFFFFFFFFFFFFFFF") which fits
	// into the already allocated intbuf with a capacity of 68 bytes.
	prec := 4
	if f.precPresent && f.prec > 4 {
	prec = f.prec
	// Compute space needed for "U+" , number, " '", character, "'".
	width := 2 + prec + 2 + utf8.UTFMax + 1
	if width > len(buf) {
	buf = make([]byte, width)
	}
	}

	// Format into buf, ending at buf[i]. Formatting numbers is easier right-to-left.
	i := len(buf)

	// For %#U we want to add a space and a quoted character at the end of the buffer.
	if f.sharp && u <= utf8.MaxRune && strconv.IsPrint(rune(u)) {
	i--
	buf[i] = '\''
	i -= utf8.RuneLen(rune(u))
	utf8.EncodeRune(buf[i:], rune(u))
	i--
	buf[i] = '\''
	i--
	buf[i] = ' '
	}
	// Format the Unicode code point u as a hexadecimal number.
	for u >= 16 {
	i--
	buf[i] = udigits[u&0xF]
	prec--
	u >>= 4
	}
	i--
	buf[i] = udigits[u]
	prec--
	// Add zeros in front of the number until requested precision is reached.
	for prec > 0 {
	i--
	buf[i] = '0'
	prec--
	}
	// Add a leading "U+".
	i--
	buf[i] = '+'
	i--
	buf[i] = 'U'

	oldZero := f.zero
	f.zero = false
	f.pad(buf[i:])
	f.zero = oldZero
	}

	// fmtInteger formats signed and unsigned integers.
	func (f *fmt) fmtInteger(u uint64, base int, isSigned bool, verb rune, digits string) {
	negative := isSigned && int64(u) < 0
	if negative {
	u = -u
	}

	buf := f.intbuf[0:]
	// The already allocated f.intbuf with a capacity of 68 bytes
	// is large enough for integer formatting when no precision or width is set.
	if f.widPresent \|\| f.precPresent {
	// Account 3 extra bytes for possible addition of a sign and "0x".
	width := 3 + f.wid + f.prec // wid and prec are always positive.
	if width > len(buf) {
	// We're going to need a bigger boat.
	buf = make([]byte, width)
	}
	}

	// Two ways to ask for extra leading zero digits: %.3d or %03d.
	// If both are specified the f.zero flag is ignored and
	// padding with spaces is used instead.
	prec := 0
	if f.precPresent {
	prec = f.prec
	// Precision of 0 and value of 0 means "print nothing" but padding.
	if prec == 0 && u == 0 {
	oldZero := f.zero
	f.zero = false
	f.writePadding(f.wid)
	f.zero = oldZero
	return
	}
	} else if f.zero && f.widPresent {
	prec = f.wid
	if negative \|\| f.plus \|\| f.space {
	prec-- // leave room for sign
	}
	}

	// Because printing is easier right-to-left: format u into buf, ending at buf[i].
	// We could make things marginally faster by splitting the 32-bit case out
	// into a separate block but it's not worth the duplication, so u has 64 bits.
	i := len(buf)
	// Use constants for the division and modulo for more efficient code.
	// Switch cases ordered by popularity.
	switch base {
	case 10:
	for u >= 10 {
	i--
	next := u / 10
	buf[i] = byte('0' + u - next*10)
	u = next
	}
	case 16:
	for u >= 16 {
	i--
	buf[i] = digits[u&0xF]
	u >>= 4
	}
	case 8:
	for u >= 8 {
	i--
	buf[i] = byte('0' + u&7)
	u >>= 3
	}
	case 2:
	for u >= 2 {
	i--
	buf[i] = byte('0' + u&1)
	u >>= 1
	}
	default:
	panic("fmt: unknown base; can't happen")
	}
	i--
	buf[i] = digits[u]
	for i > 0 && prec > len(buf)-i {
	i--
	buf[i] = '0'
	}

	// Various prefixes: 0x, -, etc.
	if f.sharp {
	switch base {
	case 2:
	// Add a leading 0b.
	i--
	buf[i] = 'b'
	i--
	buf[i] = '0'
	case 8:
	if buf[i] != '0' {
	i--
	buf[i] = '0'
	}
	case 16:
	// Add a leading 0x or 0X.
	i--
	buf[i] = digits[16]
	i--
	buf[i] = '0'
	}
	}
	if verb == 'O' {
	i--
	buf[i] = 'o'
	i--
	buf[i] = '0'
	}

	if negative {
	i--
	buf[i] = '-'
	} else if f.plus {
	i--
	buf[i] = '+'
	} else if f.space {
	i--
	buf[i] = ' '
	}

	// Left padding with zeros has already been handled like precision earlier
	// or the f.zero flag is ignored due to an explicitly set precision.
	oldZero := f.zero
	f.zero = false
	f.pad(buf[i:])
	f.zero = oldZero
	}

	// truncateString truncates the string s to the specified precision, if present.
	func (f *fmt) truncateString(s string) string {
	if f.precPresent {
	n := f.prec
	for i := range s {
	n--
	if n < 0 {
	return s[:i]
	}
	}
	}
	return s
	}

	// truncate truncates the byte slice b as a string of the specified precision, if present.
	func (f *fmt) truncate(b []byte) []byte {
	if f.precPresent {
	n := f.prec
	for i := 0; i < len(b); {
	n--
	if n < 0 {
	return b[:i]
	}
	wid := 1
	if b[i] >= utf8.RuneSelf {
	_, wid = utf8.DecodeRune(b[i:])
	}
	i += wid
	}
	}
	return b
	}

	// fmtS formats a string.
	func (f *fmt) fmtS(s string) {
	s = f.truncateString(s)
	f.padString(s)
	}

	// fmtBs formats the byte slice b as if it was formatted as string with fmtS.
	func (f *fmt) fmtBs(b []byte) {
	b = f.truncate(b)
	f.pad(b)
	}

	// fmtSbx formats a string or byte slice as a hexadecimal encoding of its bytes.
	func (f *fmt) fmtSbx(s string, b []byte, digits string) {
	length := len(b)
	if b == nil {
	// No byte slice present. Assume string s should be encoded.
	length = len(s)
	}
	// Set length to not process more bytes than the precision demands.
	if f.precPresent && f.prec < length {
	length = f.prec
	}
	// Compute width of the encoding taking into account the f.sharp and f.space flag.
	width := 2 * length
	if width > 0 {
	if f.space {
	// Each element encoded by two hexadecimals will get a leading 0x or 0X.
	if f.sharp {
	width *= 2
	}
	// Elements will be separated by a space.
	width += length - 1
	} else if f.sharp {
	// Only a leading 0x or 0X will be added for the whole string.
	width += 2
	}
	} else { // The byte slice or string that should be encoded is empty.
	if f.widPresent {
	f.writePadding(f.wid)
	}
	return
	}
	// Handle padding to the left.
	if f.widPresent && f.wid > width && !f.minus {
	f.writePadding(f.wid - width)
	}
	// Write the encoding directly into the output buffer.
	buf := *f.buf
	if f.sharp {
	// Add leading 0x or 0X.
	buf = append(buf, '0', digits[16])
	}
	var c byte
	for i := 0; i < length; i++ {
	if f.space && i > 0 {
	// Separate elements with a space.
	buf = append(buf, ' ')
	if f.sharp {
	// Add leading 0x or 0X for each element.
	buf = append(buf, '0', digits[16])
	}
	}
	if b != nil {
	c = b[i] // Take a byte from the input byte slice.
	} else {
	c = s[i] // Take a byte from the input string.
	}
	// Encode each byte as two hexadecimal digits.
	buf = append(buf, digits[c>>4], digits[c&0xF])
	}
	*f.buf = buf
	// Handle padding to the right.
	if f.widPresent && f.wid > width && f.minus {
	f.writePadding(f.wid - width)
	}
	}

	// fmtSx formats a string as a hexadecimal encoding of its bytes.
	func (f *fmt) fmtSx(s, digits string) {
	f.fmtSbx(s, nil, digits)
	}

	// fmtBx formats a byte slice as a hexadecimal encoding of its bytes.
	func (f *fmt) fmtBx(b []byte, digits string) {
	f.fmtSbx("", b, digits)
	}

	// fmtQ formats a string as a double-quoted, escaped Go string constant.
	// If f.sharp is set a raw (backquoted) string may be returned instead
	// if the string does not contain any control characters other than tab.
	func (f *fmt) fmtQ(s string) {
	s = f.truncateString(s)
	if f.sharp && strconv.CanBackquote(s) {
	f.padString("`" + s + "`")
	return
	}
	buf := f.intbuf[:0]
	if f.plus {
	f.pad(strconv.AppendQuoteToASCII(buf, s))
	} else {
	f.pad(strconv.AppendQuote(buf, s))
	}
	}

	// fmtC formats an integer as a Unicode character.
	// If the character is not valid Unicode, it will print '\ufffd'.
	func (f *fmt) fmtC(c uint64) {
	// Explicitly check whether c exceeds utf8.MaxRune since the conversion
	// of a uint64 to a rune may lose precision that indicates an overflow.
	r := rune(c)
	if c > utf8.MaxRune {
	r = utf8.RuneError
	}
	buf := f.intbuf[:0]
	f.pad(utf8.AppendRune(buf, r))
	}

	// fmtQc formats an integer as a single-quoted, escaped Go character constant.
	// If the character is not valid Unicode, it will print '\ufffd'.
	func (f *fmt) fmtQc(c uint64) {
	r := rune(c)
	if c > utf8.MaxRune {
	r = utf8.RuneError
	}
	buf := f.intbuf[:0]
	if f.plus {
	f.pad(strconv.AppendQuoteRuneToASCII(buf, r))
	} else {
	f.pad(strconv.AppendQuoteRune(buf, r))
	}
	}

	// fmtFloat formats a float64. It assumes that verb is a valid format specifier
	// for strconv.AppendFloat and therefore fits into a byte.
	func (f *fmt) fmtFloat(v float64, size int, verb rune, prec int) {
	// Explicit precision in format specifier overrules default precision.
	if f.precPresent {
	prec = f.prec
	}
	// Format number, reserving space for leading + sign if needed.
	num := strconv.AppendFloat(f.intbuf[:1], v, byte(verb), prec, size)
	if num[1] == '-' \|\| num[1] == '+' {
	num = num[1:]
	} else {
	num[0] = '+'
	}
	// f.space means to add a leading space instead of a "+" sign unless
	// the sign is explicitly asked for by f.plus.
	if f.space && num[0] == '+' && !f.plus {
	num[0] = ' '
	}
	// Special handling for infinities and NaN,
	// which don't look like a number so shouldn't be padded with zeros.
	if num[1] == 'I' \|\| num[1] == 'N' {
	oldZero := f.zero
	f.zero = false
	// Remove sign before NaN if not asked for.
	if num[1] == 'N' && !f.space && !f.plus {
	num = num[1:]
	}
	f.pad(num)
	f.zero = oldZero
	return
	}
	// The sharp flag forces printing a decimal point for non-binary formats
	// and retains trailing zeros, which we may need to restore.
	if f.sharp && verb != 'b' {
	digits := 0
	switch verb {
	case 'v', 'g', 'G', 'x':
	digits = prec
	// If no precision is set explicitly use a precision of 6.
	if digits == -1 {
	digits = 6
	}
	}

	// Buffer pre-allocated with enough room for
	// exponent notations of the form "e+123" or "p-1023".
	var tailBuf [6]byte
	tail := tailBuf[:0]

	hasDecimalPoint := false
	sawNonzeroDigit := false
	// Starting from i = 1 to skip sign at num[0].
	for i := 1; i < len(num); i++ {
	switch num[i] {
	case '.':
	hasDecimalPoint = true
	case 'p', 'P':
	tail = append(tail, num[i:]...)
	num = num[:i]
	case 'e', 'E':
	if verb != 'x' && verb != 'X' {
	tail = append(tail, num[i:]...)
	num = num[:i]
	break
	}
	fallthrough
	default:
	if num[i] != '0' {
	sawNonzeroDigit = true
	}
	// Count significant digits after the first non-zero digit.
	if sawNonzeroDigit {
	digits--
	}
	}
	}
	if !hasDecimalPoint {
	// Leading digit 0 should contribute once to digits.
	if len(num) == 2 && num[1] == '0' {
	digits--
	}
	num = append(num, '.')
	}
	for digits > 0 {
	num = append(num, '0')
	digits--
	}
	num = append(num, tail...)
	}
	// We want a sign if asked for and if the sign is not positive.
	if f.plus \|\| num[0] != '+' {
	// If we're zero padding to the left we want the sign before the leading zeros.
	// Achieve this by writing the sign out and then padding the unsigned number.
	if f.zero && f.widPresent && f.wid > len(num) {
	f.buf.writeByte(num[0])
	f.writePadding(f.wid - len(num))
	f.buf.write(num[1:])
	return
	}
	f.pad(num)
	return
	}
	// No sign to show and the number is positive; just print the unsigned number.
	f.pad(num[1:])
	}