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