mattkretz
commented
3 weeks ago This paper addresses #1584
Open mattkretz opened 3 weeks ago
mattkretz
commented
3 weeks ago This paper addresses #1584
mattkretz
commented
1 week ago Chair: Matthias Kretz
Champion: Matthias Kretz
POLL: Constant expressions (not constant folding) may not use greater precision and range than the type. => Reproducibility in constant expressions. If you need more precision and range use std::float128_t in constant expressions.
| SF | F | N | A | SA |
|---|---|---|---|---|
| 4 | 2 | 0 | 0 | 0 |
# of Participants: 6 Outcome: Strong consensus.
POLL: Constant folding behavior follows runtime evaluation behavior.
| SF | F | N | A | SA |
|---|---|---|---|---|
| 5 | 1 | 0 | 0 | 0 |
# of Participants: 6 Outcome: Strong consensus.
POLL: Literals are always rounded to their types. (Never can a higher
precision and range value be used in subsequent operations. 1.1f + x where
x is a double cannot be evaluated as 1.1 + x.)
| SF | F | N | A | SA |
|---|---|---|---|---|
| 3 | 3 | 0 | 0 | 0 |
# of Participants: 6 Outcome: Strong consensus.
POLL: We should consider not allowing excess precision in runtime
evaluation at all (except if we introduce an "attribute" that controls this, as
documented in 60559). Every binary operation on floating-point is rounded once
to the precision and range of its type (decltype(expr)).
| SF | F | N | A | SA |
|---|---|---|---|---|
| 2 | 3 | 0 | 1 | 0 |
# of Participants: 6 Outcome: Consensus in favor.
POLL: Excess precision in runtime evaluation should be a permissible optimization for implementations. The implementation choice of what intermediate type was used is reflected by FLT_EVAL_METHOD (potentially as a different trait or with the extended values as defined in C23 Annex H).
| SF | F | N | A | SA |
|---|---|---|---|---|
| 1 | 2 | 1 | 2 | 0 |
# of Participants: 6 Outcome: No consensus.
POLL: Comparison operators should always round their operands to the
precision and range of their types in case excess precision is used. In
addition to operators we expect the <cmath> comparison functions to have the
same behavior (std::isless(a, b) etc...)
| SF | F | N | A | SA |
|---|---|---|---|---|
| 3 | 0 | 2 | 0 | 1 |
# of Participants: 6 Outcome: No consensus. SA: Not worth differing from C in this. x87 does comparison on long double types.
jfbastien
commented
1 week ago Seen in EWG on Wednesday:
Poll: CWG2752 / P3488: Floating-Point Excess Precision, FLT_EVAL_METHOD must always be 0. |
SF | F | N | A | SA |
|---|---|---|---|---|---|
| 2 | 5 | 5 | 4 | 4 |
Result: not consensus
Poll: CWG2752 / P3488: Floating-Point Excess Precision, FLT_EVAL_METHOD can have any value allowed by C (this poll requires fixing some Core wording).
| SF | F | N | A | SA |
|---|---|---|---|---|
| 0 | 5 | 8 | 4 | 4 |
Result: not consensus
P3488R0 Floating-Point Excess Precision (Matthias Kretz)