/usr/share/gocode/src/golang.org/x/text/width/gen.go is in golang-golang-x-text-dev 0.0~git20170627.0.6353ef0-1ubuntu2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 | // 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.
// +build ignore
// This program generates the trie for width operations. The generated table
// includes width category information as well as the normalization mappings.
package main
import (
"bytes"
"fmt"
"io"
"log"
"math"
"unicode/utf8"
"golang.org/x/text/internal/gen"
"golang.org/x/text/internal/triegen"
)
// See gen_common.go for flags.
func main() {
gen.Init()
genTables()
genTests()
gen.Repackage("gen_trieval.go", "trieval.go", "width")
gen.Repackage("gen_common.go", "common_test.go", "width")
}
func genTables() {
t := triegen.NewTrie("width")
// fold and inverse mappings. See mapComment for a description of the format
// of each entry. Add dummy value to make an index of 0 mean no mapping.
inverse := [][4]byte{{}}
mapping := map[[4]byte]int{[4]byte{}: 0}
getWidthData(func(r rune, tag elem, alt rune) {
idx := 0
if alt != 0 {
var buf [4]byte
buf[0] = byte(utf8.EncodeRune(buf[1:], alt))
s := string(r)
buf[buf[0]] ^= s[len(s)-1]
var ok bool
if idx, ok = mapping[buf]; !ok {
idx = len(mapping)
if idx > math.MaxUint8 {
log.Fatalf("Index %d does not fit in a byte.", idx)
}
mapping[buf] = idx
inverse = append(inverse, buf)
}
}
t.Insert(r, uint64(tag|elem(idx)))
})
w := &bytes.Buffer{}
gen.WriteUnicodeVersion(w)
sz, err := t.Gen(w)
if err != nil {
log.Fatal(err)
}
sz += writeMappings(w, inverse)
fmt.Fprintf(w, "// Total table size %d bytes (%dKiB)\n", sz, sz/1024)
gen.WriteGoFile(*outputFile, "width", w.Bytes())
}
const inverseDataComment = `
// inverseData contains 4-byte entries of the following format:
// <length> <modified UTF-8-encoded rune> <0 padding>
// The last byte of the UTF-8-encoded rune is xor-ed with the last byte of the
// UTF-8 encoding of the original rune. Mappings often have the following
// pattern:
// Ａ -> A (U+FF21 -> U+0041)
// Ｂ -> B (U+FF22 -> U+0042)
// ...
// By xor-ing the last byte the same entry can be shared by many mappings. This
// reduces the total number of distinct entries by about two thirds.
// The resulting entry for the aforementioned mappings is
// { 0x01, 0xE0, 0x00, 0x00 }
// Using this entry to map U+FF21 (UTF-8 [EF BC A1]), we get
// E0 ^ A1 = 41.
// Similarly, for U+FF22 (UTF-8 [EF BC A2]), we get
// E0 ^ A2 = 42.
// Note that because of the xor-ing, the byte sequence stored in the entry is
// not valid UTF-8.`
func writeMappings(w io.Writer, data [][4]byte) int {
fmt.Fprintln(w, inverseDataComment)
fmt.Fprintf(w, "var inverseData = [%d][4]byte{\n", len(data))
for _, x := range data {
fmt.Fprintf(w, "{ 0x%02x, 0x%02x, 0x%02x, 0x%02x },\n", x[0], x[1], x[2], x[3])
}
fmt.Fprintln(w, "}")
return len(data) * 4
}
func genTests() {
w := &bytes.Buffer{}
fmt.Fprintf(w, "\nvar mapRunes = map[rune]struct{r rune; e elem}{\n")
getWidthData(func(r rune, tag elem, alt rune) {
if alt != 0 {
fmt.Fprintf(w, "\t0x%X: {0x%X, 0x%X},\n", r, alt, tag)
}
})
fmt.Fprintln(w, "}")
gen.WriteGoFile("runes_test.go", "width", w.Bytes())
}
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