Add a C API by lemire · Pull Request #897 · simdutf/simdutf

lemire · 2026-01-04T21:38:56Z

Short title (summary):
Add a C API

Description

This PR adds a C API to simdutf. Amazingly, I cannot find a corresponding open issue.

Note that simdutf itself depends on the C++ library.

Purpose: This should make it easy to call simdutf from Swift, Go and friends.

To keep it simpler, I am not adding the feature macros to it... I am concerned that it will add much complexity, although it can be done later.

See #893

cc @MahdiBM

Type of change

Copilot

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 5 comments.

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Co-authored-by: Copilot <[email protected]>

pauldreik · 2026-01-05T08:27:56Z

+#include <stdbool.h>
+#include <stdint.h>
+
+#ifdef __has_include


this seems to be a C23 feature, so I think it must be changed or we require C23.
https://en.cppreference.com/w/c/preprocessor/include

this seems to be a C23 feature, so I think it must be changed or we require C23.

Formally, you are correct, but both clang and gcc have supported __has_include for a really long time.

https://godbolt.org/z/895hcr7ff

The issue is that uchar.his C11 but Apple does not have the header. I don't know why.

lemire · 2026-01-05T21:34:09Z

@pauldreik Making as 'ready for review'.

pauldreik

I tested the amalgamate script, it failed with:

FileNotFoundError: [Errno 2] No such file or directory: '/home/pauldreik/code/delaktig/simdutf/singleheader/simdutf_c.h'

pauldreik · 2026-01-05T22:21:59Z

@lemire I took the liberty to push some clang format changes and ci job, hope you don't mind.

lemire · 2026-01-05T23:00:40Z

@pauldreik I don't mind if you push stuff, but the rvv CI changes seem to fail.

lemire · 2026-01-05T23:08:59Z

so, I think row 4 and 6 should be deleted. agree?

Maybe I misunderstand you. Here is what I think. If I write a function definition in C++ and I want it to be callable from C, then I put it inside an extern 'C' scope.

lemire · 2026-01-05T23:15:23Z

@pauldreik I pushed two changes.

Fixed a logic error in the amalgamation script (thanks)
Marked the C API as experimental (meaning we warn about possible bugs)

pauldreik · 2026-01-06T08:25:24Z

@pauldreik I don't mind if you push stuff, but the rvv CI changes seem to fail.

it was not my push that caused the failure, I pushed a fix for one of the three failing riscv jobs. I have now pushed fixes for the remaining two.

pauldreik · 2026-01-06T08:29:13Z

so, I think row 4 and 6 should be deleted. agree?

Maybe I misunderstand you. Here is what I think. If I write a function definition in C++ and I want it to be callable from C, then I put it inside an extern 'C' scope.

It is the declaration that needs to be in extern C. But that is not what I am after here, it is that the wrapping of extern C around the include is at best redundant and at worst wrong (since it unconditionally puts everything, including not functions, from the header file in extern C)

this is to prove that the amalgamation as described in the README works both for C++ and C.

This reverts commit 032c633.

lemire · 2026-01-06T14:06:03Z

@pauldreik I did not see that extern C at first, in the test file. Sorry. I just removed it.

It did not make sense, I agree.

pauldreik · 2026-01-06T15:02:58Z

no problem! are we good to merge then?

lemire · 2026-01-06T15:56:12Z

Merged !

lemire added 2 commits January 4, 2026 16:30

Add a C API

8ecf2ac

lint.

08699a8

lemire mentioned this pull request Jan 4, 2026

Make simdutf trivial to use in Swift, through Swift's C++ interoperability #893

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12 tasks

workaround

724396f

lemire requested review from Copilot and pauldreik January 4, 2026 21:43

tweaks

792a1c4

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lemire added 3 commits January 4, 2026 17:04

fixing the paths

a22a40c

lint

aa56035

lint

599e2b0

lemire requested a review from Copilot January 4, 2026 23:38

Copilot started reviewing on behalf of lemire January 4, 2026 23:51 View session

Copilot AI reviewed Jan 4, 2026

View reviewed changes

Comment thread singleheader/amalgamate.py Outdated

Comment thread include/simdutf_c.h

Comment thread README.md Outdated

Comment thread tests/simdutf_c_tests.cpp Outdated

Comment thread tests/simdutf_c_tests.cpp

lemire and others added 4 commits January 4, 2026 20:10

Update README.md

a8b5e3a

Co-authored-by: Copilot <[email protected]>

Update singleheader/amalgamate.py

6563b60

Co-authored-by: Copilot <[email protected]>

hack to make the amalgamation work.

a62ea6a

Merge branch 'add_c_api' of github.com:simdutf/simdutf into add_c_api

54fbfbb

pauldreik reviewed Jan 5, 2026

View reviewed changes

added new test in pure C

fb60176

lemire changed the title ~~Add a C API [WIP]~~ Add a C API Jan 5, 2026

lemire marked this pull request as ready for review January 5, 2026 21:33

lemire requested a review from pauldreik January 5, 2026 21:33

pauldreik added 5 commits January 5, 2026 22:40

add c file extension to clang format

86f8d67

clang format the c files

305ebf8

return platform independent exit status

cdcaa27

ci: set c23 in latest standard job

9475d13

ci: set c standard to 11

0c33566

pauldreik reviewed Jan 5, 2026

View reviewed changes

Comment thread tests/simdutf_c_tests.cpp Outdated

Comment thread README.md

Update rvv-256-gcc-14.yml

1cd7d3c

marking the C implementation as experimental. fixing amalgamate.py bug.

5e3a925

lemire and others added 3 commits January 5, 2026 18:24

simplifiying

39a1fda

correction.

d5a969a

ci: fix two remaining riscv jobs

43a6a91

pauldreik and others added 5 commits January 6, 2026 09:52

ci: add amalgamation demo

2ab3b74

this is to prove that the amalgamation as described in the README works both for C++ and C.

ci: TEMPORARY try clang 20 riscv job

032c633

fixup! ci: fix two remaining riscv jobs

2672a04

Revert "ci: TEMPORARY try clang 20 riscv job"

bbdcbde

This reverts commit 032c633.

removing bad extern c

cdd550e

lemire merged commit 2542805 into master Jan 6, 2026
106 checks passed

pauldreik deleted the add_c_api branch January 6, 2026 19:29

BrewTestBot mentioned this pull request Jan 13, 2026

simdutf 8.0.0 Homebrew/homebrew-core#262558

Merged

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