P3666 R2 Bit-precise integers

[wg21bot]

P3666r0 Bit-precise integers (Jan Schultke)

[wg21bot]

P3666R1 Bit-precise integers (Jan Schultke)

[NinaRanns]

Seen by SG22 (minutes)

/Poll/: Do you agree with the author’s position on fundamental types being better than class template for _BitInt>?
Any objections to unanimous consent? /None/

/Poll/: Do you agree with allowing 0wb = _BitInt(1) and enum E : _BitInt(N), assuming C adopts N3699 and N3705?
Any objections to unanimous consent? /None/

/Poll/: Do you agree with keeping UB on signed integer overflow for _BitInt?
Any objections to unanimous consent? /None/

/Poll/: Do you agree that WG21 keep all implicit conversions for _BitInt?
Any objections to unanimous consent? /None/

/Poll/: Do you agree that WG21 keep the lower limit on the value of BITINT_MAXWIDTH from C?
Any objections to unanimous consent? /None/

/Poll/: Do you agree that WG21 should add a _BitInt keyword?
Any objections to unanimous consent? /None/

Group thinks it's premature to weigh in on what we think about an alias template. We do want to check for C/C++ compatibility if there is a concrete proposal of an alias template.

Group agrees that we want to pursue compatibility between C and C++ with regards to _BitInt

[mattkretz]

P3666R1: Bit-precise integers

2025-11-05 SG6 Minutes

Chair: Matthias Kretz | Lisa Lippincott

Champion: Jan Schultke

Summary

• Parameter passing concerns for large _BitInt(N) for T f(T)-like
  functions. More memcpy than actual work?

• Concern about C not extending library functions for _BitInt whereas C++
  would generalize all of its library.

• Concern about the semantics of _BitInt; but if we want different semantics
  we want a different type.

Polls

POLL: Let _BitInt have the exact same semantics as in C.

SF	F	N	A	SA
7	2	0	0	0

• Author Position: SF
• Outcome: Strong consensus in favor

POLL: Forward P3666R1 to LEWG.

SF	F	N	A	SA
5	2	1	1	0

• Author Position: SF
• Outcome: Strong consensus