You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
72 lines
1.9 KiB
72 lines
1.9 KiB
package brotli
|
|
|
|
/* Copyright 2013 Google Inc. All Rights Reserved.
|
|
|
|
Distributed under MIT license.
|
|
See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
|
|
*/
|
|
|
|
/* Heuristics for deciding about the UTF8-ness of strings. */
|
|
|
|
const kMinUTF8Ratio float64 = 0.75
|
|
|
|
/* Returns 1 if at least min_fraction of the bytes between pos and
|
|
pos + length in the (data, mask) ring-buffer is UTF8-encoded, otherwise
|
|
returns 0. */
|
|
func parseAsUTF8(symbol *int, input []byte, size uint) uint {
|
|
/* ASCII */
|
|
if input[0]&0x80 == 0 {
|
|
*symbol = int(input[0])
|
|
if *symbol > 0 {
|
|
return 1
|
|
}
|
|
}
|
|
|
|
/* 2-byte UTF8 */
|
|
if size > 1 && input[0]&0xE0 == 0xC0 && input[1]&0xC0 == 0x80 {
|
|
*symbol = (int(input[0])&0x1F)<<6 | int(input[1])&0x3F
|
|
if *symbol > 0x7F {
|
|
return 2
|
|
}
|
|
}
|
|
|
|
/* 3-byte UFT8 */
|
|
if size > 2 && input[0]&0xF0 == 0xE0 && input[1]&0xC0 == 0x80 && input[2]&0xC0 == 0x80 {
|
|
*symbol = (int(input[0])&0x0F)<<12 | (int(input[1])&0x3F)<<6 | int(input[2])&0x3F
|
|
if *symbol > 0x7FF {
|
|
return 3
|
|
}
|
|
}
|
|
|
|
/* 4-byte UFT8 */
|
|
if size > 3 && input[0]&0xF8 == 0xF0 && input[1]&0xC0 == 0x80 && input[2]&0xC0 == 0x80 && input[3]&0xC0 == 0x80 {
|
|
*symbol = (int(input[0])&0x07)<<18 | (int(input[1])&0x3F)<<12 | (int(input[2])&0x3F)<<6 | int(input[3])&0x3F
|
|
if *symbol > 0xFFFF && *symbol <= 0x10FFFF {
|
|
return 4
|
|
}
|
|
}
|
|
|
|
/* Not UTF8, emit a special symbol above the UTF8-code space */
|
|
*symbol = 0x110000 | int(input[0])
|
|
|
|
return 1
|
|
}
|
|
|
|
/* Returns 1 if at least min_fraction of the data is UTF8-encoded.*/
|
|
func isMostlyUTF8(data []byte, pos uint, mask uint, length uint, min_fraction float64) bool {
|
|
var size_utf8 uint = 0
|
|
var i uint = 0
|
|
for i < length {
|
|
var symbol int
|
|
var current_data []byte
|
|
current_data = data[(pos+i)&mask:]
|
|
var bytes_read uint = parseAsUTF8(&symbol, current_data, length-i)
|
|
i += bytes_read
|
|
if symbol < 0x110000 {
|
|
size_utf8 += bytes_read
|
|
}
|
|
}
|
|
|
|
return float64(size_utf8) > min_fraction*float64(length)
|
|
}
|