chromium/third_party/icu/source/common/unormcmp.cpp

// © 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:  unormcmp.cpp
*   encoding:   UTF-8
*   tab size:   8 (not used)
*   indentation:4
*
*   created on: 2004sep13
*   created by: Markus W. Scherer
*
*   unorm_compare() function moved here from unorm.cpp for better modularization.
*   Depends on both normalization and case folding.
*   Allows unorm.cpp to not depend on any character properties code.
*/

#include "unicode/utypes.h"

#if !UCONFIG_NO_NORMALIZATION

#include "unicode/unorm.h"
#include "unicode/ustring.h"
#include "cmemory.h"
#include "normalizer2impl.h"
#include "ucase.h"
#include "uprops.h"
#include "ustr_imp.h"

U_NAMESPACE_USE

/* compare canonically equivalent ------------------------------------------- */

/*
 * Compare two strings for canonical equivalence.
 * Further options include case-insensitive comparison and
 * code point order (as opposed to code unit order).
 *
 * In this function, canonical equivalence is optional as well.
 * If canonical equivalence is tested, then both strings must fulfill
 * the FCD check.
 *
 * Semantically, this is equivalent to
 *   strcmp[CodePointOrder](NFD(foldCase(s1)), NFD(foldCase(s2)))
 * where code point order, NFD and foldCase are all optional.
 *
 * String comparisons almost always yield results before processing both strings
 * completely.
 * They are generally more efficient working incrementally instead of
 * performing the sub-processing (strlen, normalization, case-folding)
 * on the entire strings first.
 *
 * It is also unnecessary to not normalize identical characters.
 *
 * This function works in principle as follows:
 *
 * loop {
 *   get one code unit c1 from s1 (-1 if end of source)
 *   get one code unit c2 from s2 (-1 if end of source)
 *
 *   if(either string finished) {
 *     return result;
 *   }
 *   if(c1==c2) {
 *     continue;
 *   }
 *
 *   // c1!=c2
 *   try to decompose/case-fold c1/c2, and continue if one does;
 *
 *   // still c1!=c2 and neither decomposes/case-folds, return result
 *   return c1-c2;
 * }
 *
 * When a character decomposes, then the pointer for that source changes to
 * the decomposition, pushing the previous pointer onto a stack.
 * When the end of the decomposition is reached, then the code unit reader
 * pops the previous source from the stack.
 * (Same for case-folding.)
 *
 * This is complicated further by operating on variable-width UTF-16.
 * The top part of the loop works on code units, while lookups for decomposition
 * and case-folding need code points.
 * Code points are assembled after the equality/end-of-source part.
 * The source pointer is only advanced beyond all code units when the code point
 * actually decomposes/case-folds.
 *
 * If we were on a trail surrogate unit when assembling a code point,
 * and the code point decomposes/case-folds, then the decomposition/folding
 * result must be compared with the part of the other string that corresponds to
 * this string's lead surrogate.
 * Since we only assemble a code point when hitting a trail unit when the
 * preceding lead units were identical, we back up the other string by one unit
 * in such a case.
 *
 * The optional code point order comparison at the end works with
 * the same fix-up as the other code point order comparison functions.
 * See ustring.c and the comment near the end of this function.
 *
 * Assumption: A decomposition or case-folding result string never contains
 * a single surrogate. This is a safe assumption in the Unicode Standard.
 * Therefore, we do not need to check for surrogate pairs across
 * decomposition/case-folding boundaries.
 *
 * Further assumptions (see verifications tstnorm.cpp):
 * The API function checks for FCD first, while the core function
 * first case-folds and then decomposes. This requires that case-folding does not
 * un-FCD any strings.
 *
 * The API function may also NFD the input and turn off decomposition.
 * This requires that case-folding does not un-NFD strings either.
 *
 * TODO If any of the above two assumptions is violated,
 * then this entire code must be re-thought.
 * If this happens, then a simple solution is to case-fold both strings up front
 * and to turn off UNORM_INPUT_IS_FCD.
 * We already do this when not both strings are in FCD because makeFCD
 * would be a partial NFD before the case folding, which does not work.
 * Note that all of this is only a problem when case-folding _and_
 * canonical equivalence come together.
 * (Comments in unorm_compare() are more up to date than this TODO.)
 */

/* stack element for previous-level source/decomposition pointers */
struct CmpEquivLevel { … };
CmpEquivLevel;

/**
 * Internal option for unorm_cmpEquivFold() for decomposing.
 * If not set, just do strcasecmp().
 */
#define _COMPARE_EQUIV …

/* internal function */
static int32_t
unorm_cmpEquivFold(const char16_t *s1, int32_t length1,
                   const char16_t *s2, int32_t length2,
                   uint32_t options,
                   UErrorCode *pErrorCode) { … }

static
UBool _normalize(const Normalizer2 *n2, const char16_t *s, int32_t length,
                UnicodeString &normalized, UErrorCode *pErrorCode) { … }

U_CAPI int32_t U_EXPORT2
unorm_compare(const char16_t *s1, int32_t length1,
              const char16_t *s2, int32_t length2,
              uint32_t options,
              UErrorCode *pErrorCode) { … }

#endif /* #if !UCONFIG_NO_NORMALIZATION */