499 lines
12 KiB
Go
499 lines
12 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package fmt
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import (
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"strconv"
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"unicode/utf8"
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)
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const (
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ldigits = "0123456789abcdefx"
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udigits = "0123456789ABCDEFX"
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)
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const (
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signed = true
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unsigned = false
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)
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// flags placed in a separate struct for easy clearing.
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type fmtFlags struct {
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widPresent bool
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precPresent bool
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minus bool
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plus bool
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sharp bool
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space bool
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zero bool
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// For the formats %+v %#v, we set the plusV/sharpV flags
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// and clear the plus/sharp flags since %+v and %#v are in effect
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// different, flagless formats set at the top level.
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plusV bool
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sharpV bool
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}
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// A fmt is the raw formatter used by Printf etc.
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// It prints into a buffer that must be set up separately.
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type fmt struct {
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buf *buffer
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fmtFlags
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wid int // width
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prec int // precision
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// intbuf is large enought to store %b of an int64 with a sign and
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// avoids padding at the end of the struct on 32 bit architectures.
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intbuf [68]byte
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}
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func (f *fmt) clearflags() {
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f.fmtFlags = fmtFlags{}
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}
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func (f *fmt) init(buf *buffer) {
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f.buf = buf
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f.clearflags()
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}
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// writePadding generates n bytes of padding.
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func (f *fmt) writePadding(n int) {
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if n <= 0 { // No padding bytes needed.
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return
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}
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buf := *f.buf
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oldLen := len(buf)
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newLen := oldLen + n
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// Make enough room for padding.
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if newLen > cap(buf) {
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buf = make(buffer, cap(buf)*2+n)
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copy(buf, *f.buf)
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}
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// Decide which byte the padding should be filled with.
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padByte := byte(' ')
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if f.zero {
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padByte = byte('0')
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}
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// Fill padding with padByte.
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padding := buf[oldLen:newLen]
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for i := range padding {
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padding[i] = padByte
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}
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*f.buf = buf[:newLen]
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}
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// pad appends b to f.buf, padded on left (!f.minus) or right (f.minus).
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func (f *fmt) pad(b []byte) {
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if !f.widPresent || f.wid == 0 {
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f.buf.Write(b)
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return
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}
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width := f.wid - utf8.RuneCount(b)
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if !f.minus {
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// left padding
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f.writePadding(width)
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f.buf.Write(b)
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} else {
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// right padding
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f.buf.Write(b)
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f.writePadding(width)
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}
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}
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// padString appends s to f.buf, padded on left (!f.minus) or right (f.minus).
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func (f *fmt) padString(s string) {
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if !f.widPresent || f.wid == 0 {
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f.buf.WriteString(s)
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return
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}
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width := f.wid - utf8.RuneCountInString(s)
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if !f.minus {
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// left padding
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f.writePadding(width)
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f.buf.WriteString(s)
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} else {
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// right padding
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f.buf.WriteString(s)
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f.writePadding(width)
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}
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}
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// fmt_boolean formats a boolean.
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func (f *fmt) fmt_boolean(v bool) {
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if v {
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f.padString("true")
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} else {
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f.padString("false")
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}
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}
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// fmt_unicode formats a uint64 as "U+0078" or with f.sharp set as "U+0078 'x'".
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func (f *fmt) fmt_unicode(u uint64) {
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buf := f.intbuf[0:]
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// With default precision set the maximum needed buf length is 18
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// for formatting -1 with %#U ("U+FFFFFFFFFFFFFFFF") which fits
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// into the already allocated intbuf with a capacity of 68 bytes.
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prec := 4
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if f.precPresent && f.prec > 4 {
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prec = f.prec
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// Compute space needed for "U+" , number, " '", character, "'".
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width := 2 + prec + 2 + utf8.UTFMax + 1
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if width > len(buf) {
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buf = make([]byte, width)
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}
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}
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// Format into buf, ending at buf[i]. Formatting numbers is easier right-to-left.
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i := len(buf)
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// For %#U we want to add a space and a quoted character at the end of the buffer.
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if f.sharp && u <= utf8.MaxRune && strconv.IsPrint(rune(u)) {
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i--
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buf[i] = '\''
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i -= utf8.RuneLen(rune(u))
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utf8.EncodeRune(buf[i:], rune(u))
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i--
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buf[i] = '\''
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i--
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buf[i] = ' '
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}
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// Format the Unicode code point u as a hexadecimal number.
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for u >= 16 {
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i--
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buf[i] = udigits[u&0xF]
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prec--
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u >>= 4
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}
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i--
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buf[i] = udigits[u]
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prec--
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// Add zeros in front of the number until requested precision is reached.
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for prec > 0 {
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i--
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buf[i] = '0'
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prec--
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}
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// Add a leading "U+".
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i--
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buf[i] = '+'
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i--
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buf[i] = 'U'
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oldZero := f.zero
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f.zero = false
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f.pad(buf[i:])
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f.zero = oldZero
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}
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// fmt_integer formats signed and unsigned integers.
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func (f *fmt) fmt_integer(u uint64, base int, isSigned bool, digits string) {
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negative := isSigned && int64(u) < 0
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if negative {
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u = -u
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}
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buf := f.intbuf[0:]
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// The already allocated f.intbuf with a capacity of 68 bytes
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// is large enough for integer formatting when no precision or width is set.
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if f.widPresent || f.precPresent {
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// Account 3 extra bytes for possible addition of a sign and "0x".
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width := 3 + f.wid + f.prec // wid and prec are always positive.
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if width > len(buf) {
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// We're going to need a bigger boat.
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buf = make([]byte, width)
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}
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}
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// Two ways to ask for extra leading zero digits: %.3d or %03d.
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// If both are specified the f.zero flag is ignored and
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// padding with spaces is used instead.
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prec := 0
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if f.precPresent {
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prec = f.prec
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// Precision of 0 and value of 0 means "print nothing" but padding.
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if prec == 0 && u == 0 {
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oldZero := f.zero
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f.zero = false
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f.writePadding(f.wid)
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f.zero = oldZero
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return
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}
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} else if f.zero && f.widPresent {
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prec = f.wid
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if negative || f.plus || f.space {
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prec-- // leave room for sign
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}
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}
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// Because printing is easier right-to-left: format u into buf, ending at buf[i].
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// We could make things marginally faster by splitting the 32-bit case out
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// into a separate block but it's not worth the duplication, so u has 64 bits.
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i := len(buf)
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// Use constants for the division and modulo for more efficient code.
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// Switch cases ordered by popularity.
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switch base {
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case 10:
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for u >= 10 {
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i--
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next := u / 10
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buf[i] = byte('0' + u - next*10)
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u = next
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}
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case 16:
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for u >= 16 {
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i--
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buf[i] = digits[u&0xF]
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u >>= 4
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}
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case 8:
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for u >= 8 {
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i--
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buf[i] = byte('0' + u&7)
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u >>= 3
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}
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case 2:
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for u >= 2 {
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i--
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buf[i] = byte('0' + u&1)
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u >>= 1
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}
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default:
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panic("fmt: unknown base; can't happen")
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}
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i--
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buf[i] = digits[u]
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for i > 0 && prec > len(buf)-i {
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i--
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buf[i] = '0'
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}
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// Various prefixes: 0x, -, etc.
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if f.sharp {
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switch base {
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case 8:
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if buf[i] != '0' {
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i--
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buf[i] = '0'
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}
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case 16:
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// Add a leading 0x or 0X.
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i--
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buf[i] = digits[16]
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i--
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buf[i] = '0'
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}
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}
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if negative {
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i--
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buf[i] = '-'
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} else if f.plus {
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i--
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buf[i] = '+'
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} else if f.space {
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i--
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buf[i] = ' '
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}
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// Left padding with zeros has already been handled like precision earlier
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// or the f.zero flag is ignored due to an explicitly set precision.
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oldZero := f.zero
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f.zero = false
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f.pad(buf[i:])
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f.zero = oldZero
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}
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// truncate truncates the string to the specified precision, if present.
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func (f *fmt) truncate(s string) string {
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if f.precPresent {
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n := f.prec
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for i := range s {
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n--
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if n < 0 {
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return s[:i]
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}
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}
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}
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return s
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}
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// fmt_s formats a string.
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func (f *fmt) fmt_s(s string) {
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s = f.truncate(s)
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f.padString(s)
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}
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// fmt_sbx formats a string or byte slice as a hexadecimal encoding of its bytes.
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func (f *fmt) fmt_sbx(s string, b []byte, digits string) {
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length := len(b)
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if b == nil {
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// No byte slice present. Assume string s should be encoded.
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length = len(s)
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}
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// Set length to not process more bytes than the precision demands.
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if f.precPresent && f.prec < length {
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length = f.prec
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}
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// Compute width of the encoding taking into account the f.sharp and f.space flag.
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width := 2 * length
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if width > 0 {
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if f.space {
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// Each element encoded by two hexadecimals will get a leading 0x or 0X.
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if f.sharp {
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width *= 2
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}
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// Elements will be separated by a space.
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width += length - 1
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} else if f.sharp {
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// Only a leading 0x or 0X will be added for the whole string.
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width += 2
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}
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} else { // The byte slice or string that should be encoded is empty.
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if f.widPresent {
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f.writePadding(f.wid)
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}
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return
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}
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// Handle padding to the left.
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if f.widPresent && f.wid > width && !f.minus {
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f.writePadding(f.wid - width)
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}
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// Write the encoding directly into the output buffer.
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buf := *f.buf
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if f.sharp {
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// Add leading 0x or 0X.
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buf = append(buf, '0', digits[16])
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}
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var c byte
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for i := 0; i < length; i++ {
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if f.space && i > 0 {
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// Separate elements with a space.
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buf = append(buf, ' ')
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if f.sharp {
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// Add leading 0x or 0X for each element.
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buf = append(buf, '0', digits[16])
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}
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}
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if b != nil {
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c = b[i] // Take a byte from the input byte slice.
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} else {
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c = s[i] // Take a byte from the input string.
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}
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// Encode each byte as two hexadecimal digits.
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buf = append(buf, digits[c>>4], digits[c&0xF])
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}
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*f.buf = buf
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// Handle padding to the right.
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if f.widPresent && f.wid > width && f.minus {
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f.writePadding(f.wid - width)
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}
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}
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// fmt_sx formats a string as a hexadecimal encoding of its bytes.
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func (f *fmt) fmt_sx(s, digits string) {
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f.fmt_sbx(s, nil, digits)
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}
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// fmt_bx formats a byte slice as a hexadecimal encoding of its bytes.
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func (f *fmt) fmt_bx(b []byte, digits string) {
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f.fmt_sbx("", b, digits)
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}
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// fmt_q formats a string as a double-quoted, escaped Go string constant.
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// If f.sharp is set a raw (backquoted) string may be returned instead
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// if the string does not contain any control characters other than tab.
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func (f *fmt) fmt_q(s string) {
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s = f.truncate(s)
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if f.sharp && strconv.CanBackquote(s) {
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f.padString("`" + s + "`")
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return
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}
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buf := f.intbuf[:0]
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if f.plus {
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f.pad(strconv.AppendQuoteToASCII(buf, s))
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} else {
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f.pad(strconv.AppendQuote(buf, s))
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}
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}
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// fmt_c formats an integer as a Unicode character.
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// If the character is not valid Unicode, it will print '\ufffd'.
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func (f *fmt) fmt_c(c uint64) {
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r := rune(c)
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if c > utf8.MaxRune {
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r = utf8.RuneError
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}
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buf := f.intbuf[:0]
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w := utf8.EncodeRune(buf[:utf8.UTFMax], r)
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f.pad(buf[:w])
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}
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// fmt_qc formats an integer as a single-quoted, escaped Go character constant.
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// If the character is not valid Unicode, it will print '\ufffd'.
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func (f *fmt) fmt_qc(c uint64) {
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r := rune(c)
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if c > utf8.MaxRune {
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r = utf8.RuneError
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}
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buf := f.intbuf[:0]
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if f.plus {
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f.pad(strconv.AppendQuoteRuneToASCII(buf, r))
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} else {
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f.pad(strconv.AppendQuoteRune(buf, r))
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}
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}
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// fmt_float formats a float64. It assumes that verb is a valid format specifier
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// for strconv.AppendFloat and therefore fits into a byte.
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func (f *fmt) fmt_float(v float64, size int, verb rune, prec int) {
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// Explicit precision in format specifier overrules default precision.
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if f.precPresent {
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prec = f.prec
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}
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// Format number, reserving space for leading + sign if needed.
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num := strconv.AppendFloat(f.intbuf[:1], v, byte(verb), prec, size)
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if num[1] == '-' || num[1] == '+' {
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num = num[1:]
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} else {
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num[0] = '+'
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}
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// f.space means to add a leading space instead of a "+" sign unless
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// the sign is explicitly asked for by f.plus.
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if f.space && num[0] == '+' && !f.plus {
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num[0] = ' '
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}
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// Special handling for infinities and NaN,
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// which don't look like a number so shouldn't be padded with zeros.
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if num[1] == 'I' || num[1] == 'N' {
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oldZero := f.zero
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f.zero = false
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// Remove sign before NaN if not asked for.
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if num[1] == 'N' && !f.space && !f.plus {
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num = num[1:]
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}
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f.pad(num)
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f.zero = oldZero
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return
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}
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// We want a sign if asked for and if the sign is not positive.
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if f.plus || num[0] != '+' {
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// If we're zero padding to the left we want the sign before the leading zeros.
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// Achieve this by writing the sign out and then padding the unsigned number.
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if f.zero && f.widPresent && f.wid > len(num) {
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f.buf.WriteByte(num[0])
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f.writePadding(f.wid - len(num))
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f.buf.Write(num[1:])
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return
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}
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f.pad(num)
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return
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}
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// No sign to show and the number is positive; just print the unsigned number.
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f.pad(num[1:])
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}
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