Editorial: Check total nanoseconds in IsValidDuration #3186
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Make it clear that it's acceptable for an implementation to use 128-bit integers and do the validity check in terms of nanoseconds.
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Manishearth
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Manishearth
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| 1. NOTE: The above step cannot be implemented directly using floating-point arithmetic. Multiplying by 10<sup>-3</sup>, 10<sup>-6</sup>, and 10<sup>-9</sup> respectively may be imprecise when _milliseconds_, _microseconds_, or _nanoseconds_ is an unsafe integer. This multiplication can be implemented in C++ with an implementation of `std::remquo()` with sufficient bits in the quotient. String manipulation will also give an exact result, since the multiplication is by a power of 10. | ||
| 1. If abs(_normalizedSeconds_) ≥ 2<sup>53</sup>, return *false*. | ||
| 1. Let _normalizedNanoseconds_ be _days_ × 86,400 × 10<sup>9</sup> + _hours_ × 3600 × 10<sup>9</sup> + _minutes_ × 60 × 10<sup>9</sup> + _seconds_ × 10<sup>9</sup> + ℝ(𝔽(_milliseconds_)) × 10<sup>6</sup> + ℝ(𝔽(_microseconds_)) × 10<sup>3</sup> + ℝ(𝔽(_nanoseconds_)). | ||
| 1. NOTE: The above step cannot be implemented directly using 64-bit floating-point arithmetic. Multiplying by 10<sup>-3</sup>, 10<sup>-6</sup>, and 10<sup>-9</sup> respectively may be imprecise when _milliseconds_, _microseconds_, or _nanoseconds_ is an unsafe integer. The step can be implemented using 128-bit integers. It could also be implemented in C++ with an implementation of `std::remquo()` with sufficient bits in the quotient. String manipulation will also give an exact result, since the multiplication is by a power of 10. |
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"using 128 bit integers and performing all arithmetic on nanosecond values" maybe?
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Manishearth
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Make it clear that it's acceptable for an implementation to use 128-bit integers and do the validity check in terms of nanoseconds.
Closes #3177