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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
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)
}
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