today in "cross-language RPC": Rust and Swift have a different bit pattern for pi
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@ju Ya
0x40490FDB Rust
0x40490FDA Swift
(The f64 constants are the same)
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@fasterthanlime amazing.
But now I want to know why you need PI to be equal on the bit level 😆
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@ju I don't, but some integration tests used the PI constant on both sides and.. understandably failed.
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@fasterthanlime @ju I never want to underestimate the possibility for weird corner cases in IEEE floats, but surely different bit patterns mean different values, as long as a NaN isn't involved? According to pari/gp, rust's value is closer: it's 8.7e-8 too big, while swift's is 1.5e-7 too small.
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@fasterthanlime @ju interesting
rust one is 3.1415927
swift one is 3.1415925
pi starts with 3.14159265…
seems that swift is rounding it in the wrong direction?
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Charlotte 
/Cinny 
charlotte
@fasterthanlime @ju hypothesis: this is because of the rounding mode used during parsing
rust uses standard round to zero, ties to even. the f64 representation has a 1 bit after the 23 mantissa bits that also exist on f32. closest even number is 4.0 so it rounds up
i guess swift uses round to zero or round to -Inf rounding mode for number parsing?
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