4fb47b12a7
This does the same for the ICU implementation code as was done for the
public ICU API in commit 480bec3ea6
.
162 lines
5.7 KiB
C++
162 lines
5.7 KiB
C++
// © 2016 and later: Unicode, Inc. and others.
|
|
// License & terms of use: http://www.unicode.org/copyright.html
|
|
/*
|
|
*******************************************************************************
|
|
* Copyright (C) 2001-2014, International Business Machines
|
|
* Corporation and others. All Rights Reserved.
|
|
*******************************************************************************
|
|
* file name: bocsu.h
|
|
* encoding: UTF-8
|
|
* tab size: 8 (not used)
|
|
* indentation:4
|
|
*
|
|
* Author: Markus W. Scherer
|
|
*
|
|
* Modification history:
|
|
* 05/18/2001 weiv Made into separate module
|
|
*/
|
|
|
|
#ifndef BOCSU_H
|
|
#define BOCSU_H
|
|
|
|
#include "unicode/utypes.h"
|
|
|
|
#if !UCONFIG_NO_COLLATION
|
|
|
|
U_NAMESPACE_BEGIN
|
|
|
|
class ByteSink;
|
|
|
|
U_NAMESPACE_END
|
|
|
|
/*
|
|
* "BOCSU"
|
|
* Binary Ordered Compression Scheme for Unicode
|
|
*
|
|
* Specific application:
|
|
*
|
|
* Encode a Unicode string for the identical level of a sort key.
|
|
* Restrictions:
|
|
* - byte stream (unsigned 8-bit bytes)
|
|
* - lexical order of the identical-level run must be
|
|
* the same as code point order for the string
|
|
* - avoid byte values 0, 1, 2
|
|
*
|
|
* Method: Slope Detection
|
|
* Remember the previous code point (initial 0).
|
|
* For each cp in the string, encode the difference to the previous one.
|
|
*
|
|
* With a compact encoding of differences, this yields good results for
|
|
* small scripts and UTF-like results otherwise.
|
|
*
|
|
* Encoding of differences:
|
|
* - Similar to a UTF, encoding the length of the byte sequence in the lead bytes.
|
|
* - Does not need to be friendly for decoding or random access
|
|
* (trail byte values may overlap with lead/single byte values).
|
|
* - The signedness must be encoded as the most significant part.
|
|
*
|
|
* We encode differences with few bytes if their absolute values are small.
|
|
* For correct ordering, we must treat the entire value range -10ffff..+10ffff
|
|
* in ascending order, which forbids encoding the sign and the absolute value separately.
|
|
* Instead, we split the lead byte range in the middle and encode non-negative values
|
|
* going up and negative values going down.
|
|
*
|
|
* For very small absolute values, the difference is added to a middle byte value
|
|
* for single-byte encoded differences.
|
|
* For somewhat larger absolute values, the difference is divided by the number
|
|
* of byte values available, the modulo is used for one trail byte, and the remainder
|
|
* is added to a lead byte avoiding the single-byte range.
|
|
* For large absolute values, the difference is similarly encoded in three bytes.
|
|
*
|
|
* This encoding does not use byte values 0, 1, 2, but uses all other byte values
|
|
* for lead/single bytes so that the middle range of single bytes is as large
|
|
* as possible.
|
|
* Note that the lead byte ranges overlap some, but that the sequences as a whole
|
|
* are well ordered. I.e., even if the lead byte is the same for sequences of different
|
|
* lengths, the trail bytes establish correct order.
|
|
* It would be possible to encode slightly larger ranges for each length (>1) by
|
|
* subtracting the lower bound of the range. However, that would also slow down the
|
|
* calculation.
|
|
*
|
|
* For the actual string encoding, an optimization moves the previous code point value
|
|
* to the middle of its Unicode script block to minimize the differences in
|
|
* same-script text runs.
|
|
*/
|
|
|
|
/* Do not use byte values 0, 1, 2 because they are separators in sort keys. */
|
|
#define SLOPE_MIN 3
|
|
#define SLOPE_MAX 0xff
|
|
#define SLOPE_MIDDLE 0x81
|
|
|
|
#define SLOPE_TAIL_COUNT (SLOPE_MAX-SLOPE_MIN+1)
|
|
|
|
#define SLOPE_MAX_BYTES 4
|
|
|
|
/*
|
|
* Number of lead bytes:
|
|
* 1 middle byte for 0
|
|
* 2*80=160 single bytes for !=0
|
|
* 2*42=84 for double-byte values
|
|
* 2*3=6 for 3-byte values
|
|
* 2*1=2 for 4-byte values
|
|
*
|
|
* The sum must be <=SLOPE_TAIL_COUNT.
|
|
*
|
|
* Why these numbers?
|
|
* - There should be >=128 single-byte values to cover 128-blocks
|
|
* with small scripts.
|
|
* - There should be >=20902 single/double-byte values to cover Unihan.
|
|
* - It helps CJK Extension B some if there are 3-byte values that cover
|
|
* the distance between them and Unihan.
|
|
* This also helps to jump among distant places in the BMP.
|
|
* - Four-byte values are necessary to cover the rest of Unicode.
|
|
*
|
|
* Symmetrical lead byte counts are for convenience.
|
|
* With an equal distribution of even and odd differences there is also
|
|
* no advantage to asymmetrical lead byte counts.
|
|
*/
|
|
#define SLOPE_SINGLE 80
|
|
#define SLOPE_LEAD_2 42
|
|
#define SLOPE_LEAD_3 3
|
|
#define SLOPE_LEAD_4 1
|
|
|
|
/* The difference value range for single-byters. */
|
|
#define SLOPE_REACH_POS_1 SLOPE_SINGLE
|
|
#define SLOPE_REACH_NEG_1 (-SLOPE_SINGLE)
|
|
|
|
/* The difference value range for double-byters. */
|
|
#define SLOPE_REACH_POS_2 (SLOPE_LEAD_2*SLOPE_TAIL_COUNT+(SLOPE_LEAD_2-1))
|
|
#define SLOPE_REACH_NEG_2 (-SLOPE_REACH_POS_2-1)
|
|
|
|
/* The difference value range for 3-byters. */
|
|
#define SLOPE_REACH_POS_3 (SLOPE_LEAD_3*SLOPE_TAIL_COUNT*SLOPE_TAIL_COUNT+(SLOPE_LEAD_3-1)*SLOPE_TAIL_COUNT+(SLOPE_TAIL_COUNT-1))
|
|
#define SLOPE_REACH_NEG_3 (-SLOPE_REACH_POS_3-1)
|
|
|
|
/* The lead byte start values. */
|
|
#define SLOPE_START_POS_2 (SLOPE_MIDDLE+SLOPE_SINGLE+1)
|
|
#define SLOPE_START_POS_3 (SLOPE_START_POS_2+SLOPE_LEAD_2)
|
|
|
|
#define SLOPE_START_NEG_2 (SLOPE_MIDDLE+SLOPE_REACH_NEG_1)
|
|
#define SLOPE_START_NEG_3 (SLOPE_START_NEG_2-SLOPE_LEAD_2)
|
|
|
|
/*
|
|
* Integer division and modulo with negative numerators
|
|
* yields negative modulo results and quotients that are one more than
|
|
* what we need here.
|
|
*/
|
|
#define NEGDIVMOD(n, d, m) UPRV_BLOCK_MACRO_BEGIN { \
|
|
(m)=(n)%(d); \
|
|
(n)/=(d); \
|
|
if((m)<0) { \
|
|
--(n); \
|
|
(m)+=(d); \
|
|
} \
|
|
} UPRV_BLOCK_MACRO_END
|
|
|
|
U_CFUNC UChar32
|
|
u_writeIdenticalLevelRun(UChar32 prev, const UChar *s, int32_t length, icu::ByteSink &sink);
|
|
|
|
#endif /* #if !UCONFIG_NO_COLLATION */
|
|
|
|
#endif
|