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f32/64::asinh() should return -0.0 for -0.0 #63271
Description
Activity
IEEE-754 (2008), section 9.2.1:
For the functions expm1, exp2m1, exp10m1, logp1, log2p1, log10p1, sin, tan, sinPi, atanPi, asin, atan, sinh, tanh, asinh, and atanh, f(+0) is +0 and f(−0) is −0 with no exception.
and
sinh(±∞) and asinh(±∞) are ±∞ with no exception.
I don't think adding a fast case for -0.0 is enough, codes like
println!("{}", (-1e-20f64).asinh().is_sign_negative());
also reports to be
false, considering thatasinhis a monotone function.
(-0.0 as f64).asinh().is_sign_negative()and(-1e-20f64).asinh().is_sign_negative()should have the same result considering that-0.0is strictly larger than-1e-20f.
Maybe it is more sound to add a case for any given floating number that is negative, and negate the result if it turns out not to be negative.Reacted by Timothy Gu
Currently, both of the following return false:
However, in other languages like C,
asinh(-0.0)would always return-0.0. We might need another fast case for 0.0 and -0.0 here:rust/src/libstd/f64.rs
Lines 833 to 839 in f01b9f8