============================= String Functions in LLVM-libc

Summary

This site tracks the status of the implementation of string functions in LLVM Libc. This includes a few extra functions that are not in string.h, such as functions converting strings to numbers.

Source location

The main source for string functions is located at: libc/src/string.
The source for string conversion functions is located at: libc/src/stdlib and libc/src/__support.
The tests are located at: libc/test/src/string, libc/test/src/stdlib, and libc/test/src/__support respectively.

Implementation Status

Primary memory functions

.. TODO(gchatelet): add details about the memory functions.

============= ========= Function Name Available ============= ========= bzero YES bcmp YES memcpy YES memset YES memcmp YES memmove YES ============= =========

Other Raw Memory Functions

============= ========= Function Name Available ============= ========= memchr YES memrchr YES memccpy YES mempcpy YES ============= =========

String Memory Functions

============= ========= Function Name Available ============= ========= stpcpy YES stpncpy YES strcpy YES strncpy YES strcat YES strncat YES strdup YES strndup YES ============= =========

String Examination Functions

============= ========= Function Name Available ============= ========= strlen YES strnlen YES strcmp YES strncmp YES strchr YES strrchr YES strspn YES strcspn YES strpbrk YES strstr YES strtok YES strtok_r YES ============= =========

String Conversion Functions

These functions are not in strings.h, but are still primarily string functions, and are therefore tracked along with the rest of the string functions.

The String to float functions were implemented using the Eisel-Lemire algorithm (read more about the algorithm here: The Eisel-Lemire ParseNumberF64 Algorithm <https://nigeltao.github.io/blog/2020/eisel-lemire.html>). This improved the performance of string to float and double, and allowed it to complete this comprehensive test 15% faster than glibc: Parse Number FXX Test Data <https://github.com/nigeltao/parse-number-fxx-test-data>. The test was done with LLVM-libc built on 2022-04-14 and Debian GLibc version 2.33-6. The targets libc_str_to_float_comparison_test and libc_system_str_to_float_comparison_test were built and run on the test data 10 times each, skipping the first run since it was an outlier.

============= ========= Function Name Available ============= ========= atof YES atoi YES atol YES atoll YES strtol YES strtoll YES strtoul YES strtoull YES strtof YES strtod YES strtold YES strtoimax YES strtoumax YES ============= =========

String Error Functions

============= ========= Function Name Available ============= ========= strerror strerror_s strerrorlen_s ============= =========

Localized String Functions

These functions require locale.h, and will be added when locale support is implemented in LLVM-libc.

============= ========= Function Name Available ============= ========= strcoll strxfrm ============= =========

<name>_s String Functions

Many String functions have an equivalent s version, which is intended to be more secure and safe than the previous standard. These functions add runtime error detection and overflow protection. While they can be seen as an improvement, adoption remains relatively low among users. In addition, they are being considered for removal, see Field Experience With Annex K — Bounds Checking Interfaces <http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1967.htm>. For these reasons, there is no ongoing work to implement them.