Optimizing the Usage of Normalization

1. Optimizing the Usage of Normalization Vladimir Weinstein, Markus Scherer IBM Globalization Center of Competency

2. re sumé NFD:  NFC: résumé   re sume résume   Introduction • Unicode standard has multiple ways to encode equivalent strings • Accents that don’t interact are put into a unique order 27th Internationalization and Unicode Conference

3. Introduction (contd.) • Normalization provides a way to transform a string to an unique form (NFD, NFC) • Strings that can be transformed so that they are identical in a unique form are called canonically equivalent • Time-critical applications need to minimize the number of passes over the text • ICU provides a number of tools to deal with this problem • We will use collation (language-sensitive string comparison) as an example 27th Internationalization and Unicode Conference

4. Avoiding Normalization • Force users to provide already normalized data • The performance problem does not go away • When the strings are processed many times, it could be beneficial to normalize them beforehand • Forcing users to provide a specific form can be unpopular 27th Internationalization and Unicode Conference

5. Check for Normalized Text • Most strings are already in normalized form • Quick Check is significantly faster than the full normalization • Needs canonical class data and additional data for checking the relation between a code point and a normalization form • Algorithm in UAX #15 Annex 8 (http://www.unicode.org/unicode/reports/tr15/#Annex8) 27th Internationalization and Unicode Conference

6. Normalize Incrementally • Instead of normalizing the whole string at once, normalize one piece at a time • This technique is usually combined with an incremental Quick Check • Useful for procedures with early exit, such as string comparing or scanning • Normalizes up to the next safe point 27th Internationalization and Unicode Conference

7. re sume re sume résumé Incremental Normalization: Example Non incremental normalization Initial string résumé Quick check If normalized regularly, the whole string is processed by normalization Incremental normalization Normalize just the parts that fail quick check 27th Internationalization and Unicode Conference

8. Optimized Concatenation • Simple concatenation of two normalized strings can yield a string that is not normalized • One option is to normalize the result • Unnecessarily duplicates normalization 27th Internationalization and Unicode Conference

9. Find boundaries Concatenate then normalize re + sumé re sumé Concatenate and normalize up to the boundaries r e + sumé r e sumé résumé résumé Optimized Concatenation: Example • It is enough to normalize the boundary parts • Incremental normalization is used • Much faster than redoing the whole resulting string 27th Internationalization and Unicode Conference

10. Accepting the FCD Form • Fast Composed or Decomposed form is a partially normalized form • Not unique • More lenient than NFD or NFC form • It requires that the procedure has support for all the canonically equivalent strings on input • It is possible to quick check the FCD format 27th Internationalization and Unicode Conference

11. FCD Form: Examples 27th Internationalization and Unicode Conference

12. => Å = X, Å A+ = X = X A-ring (U+00C5) Angstrom sign (U+212B) A + combining ring above (U+0041 U+030A) Canonical Closure • Preprocessing data to support the FCD form • Ensures that if data is assigned to a sequence (or a code point) it will also be assigned to all canonically equivalent FCD sequences 27th Internationalization and Unicode Conference

13. Collation • Locale specific sorting of strings • Relation between code points and collation elements • Context sensitive: • Contractions: H < Z, but CZ < CH • Expansions: OE < Œ < OF • Both: カー < カイ or キー > キイ See or read “Collation in ICU” 27th Internationalization and Unicode Conference

14. Collation Implementation in ICU • Two modes of operation: • Normalization OFF: expects the users to pass in FCD strings • Normalization ON: accepts any strings • Some locales require normalization to be turned on • Canonical closure done for contractions and regular mappings • Two important services • Sort key generation • String compare function More about ICU at the end of presentation 27th Internationalization and Unicode Conference

15. FCD Support in Collation • Much higher performance • Values assigned to a code point or a contraction are equal to those for its FCD canonically equivalent sequences • This process is time consuming, but it is done at build time • May increase data set 27th Internationalization and Unicode Conference

16. Sort Key Generation • Whole strings are processed • Sort keys tend to get reused, so the emphasis is on producing as short sort keys as possible • Two modes of operation • Normalization ON: strings are quick checked and normalization is performed, if required • Normalization OFF: depends on strings being in FCD form. The performance increases by 20% to 50% 27th Internationalization and Unicode Conference

17. No need to backup, normal situation Must backup to the start of contraction Must backup to the normalization safe spot A c z h Å c String Compare • Very time critical • Result is usually determined before fully processing both strings • First step is binary comparison for equality • When it fails, comparison continues from a safe spot 27th Internationalization and Unicode Conference

18. String Compare Continued • Normalization ON: incremental FCD check and incremental FCD normalization if required • Normalization OFF: assumes that the source strings are FCD • Most locales don’t require normalization on and thus are 20% faster by using FCD 27th Internationalization and Unicode Conference

19. International Components for Unicode • International Components for Unicode(ICU) is a library that provides robust and full-featured Unicode support • The ICU normalization engine supports the optimizations mentioned here • Library services accept FCD strings as input • Wide variety of supported platforms • Open source (X license – non-viral) • C/C++ and Java versions • http://ibm.com/software/globalization/icu 27th Internationalization and Unicode Conference

20. Conclusion • The presented techniques allow much faster string processing • In case of collation, sort key generation gets up to 50% faster than if normalizing beforehand • String compare function becomes up to 3 times faster! • May increase data size • Canonical closure preprocessing takes more time to build, but pays off at runtime 27th Internationalization and Unicode Conference

21. Q & A 27th Internationalization and Unicode Conference

22. Summary • Introduction • Avoiding normalization • Check for normalized text • Normalize incrementally • Concatenation of normalized strings • Accepting the FCD form • Implementation of collation in ICU 27th Internationalization and Unicode Conference