Make sNaN removal code tolerate different sNaN encodings #43025
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Hopefully, with this PR merged, the feature can be stabilized for Rust 1.20. r? @BurntSushi |
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r? @brson (rust_highfive has picked a reviewer for you, use r? to override) |
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Seems reasonable to me! Nice find! @bors r+ |
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📌 Commit fd40567 has been approved by |
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@bors r- |
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IEEE 754-1985 specifies the encoding of NaN floating point numbers, but while it mentions that NaNs can be subdivided into signaling and quiet ones, it doesn't fix the encoding of signaling NaNs in binary formats. This led to different implementations (CPUs) having different encodings. IEEE 754-2008 finally specified the encoding of signaling NaNs but some architectures are compatible with it, while others aren't. Certain MIPS and PA-RISC CPUs have different encodings for signaling NaNs. In order to have the float <-> binary cast feature of the std library be portable to them, we don't mask any quiet NaNs like we did before (only being compliant to IEEE 754-2008 and nothing else), but instead we simply pass a known good NaN instead. Note that in the code removed there was a bug; the 64 bit mask for quiet NaNs should have been `0x0008000000000000` instead of the specified `0x0001000000000000`.
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@bors r=BurntSushi |
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📌 Commit 3ba0f07 has been approved by |
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Jul 4, 2017
Make sNaN removal code tolerate different sNaN encodings IEEE 754-1985 specifies the encoding of NaN floating point numbers, but while it mentions that NaNs can be subdivided into signaling and quiet ones, it doesn't fix the encoding of signaling NaNs in binary formats. This led to different implementations (CPUs) having different encodings. IEEE 754-2008 finally specified the encoding of signaling NaNs but some architectures are compatible with it, while others aren't. Certain MIPS and PA-RISC CPUs have different encodings for signaling NaNs. In order to have the float <-> binary cast feature of the std library be portable to them, we don't mask any quiet NaNs like we did before (only being compliant to IEEE 754-2008 and nothing else), but instead we simply pass a known good NaN instead. Note that in the code removed there was a bug; the 64 bit mask for quiet NaNs should have been `0x0008000000000000` instead of the specified `0x0001000000000000`.
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☀️ Test successful - status-appveyor, status-travis |
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Jul 17, 2017
Stabilize float_bits_conv for Rust 1.21 Stabilizes the `float_bits_conv` lib feature for the 1.20 release of Rust. I've initially implemented the feature in #39271 and later made PR #43025 to output quiet NaNs even on platforms with different encodings, which seems to have been the only unresolved issue of the API. Due to PR #43025 being only applied to master this stabilisation can't happen for Rust 1.19 through the usual "stabilisation on beta" system that is being done for library APIs. r? @BurntSushi closes #40470.
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IEEE 754-1985 specifies the encoding of NaN floating point numbers,
but while it mentions that NaNs can be subdivided into signaling
and quiet ones, it doesn't fix the encoding of signaling NaNs in binary
formats. This led to different implementations (CPUs) having different
encodings. IEEE 754-2008 finally specified the encoding of signaling NaNs
but some architectures are compatible with it, while others aren't.
Certain MIPS and PA-RISC CPUs have different encodings for signaling
NaNs.
In order to have the float <-> binary cast feature of the std library be
portable to them, we don't mask any quiet NaNs like we did before (only
being compliant to IEEE 754-2008 and nothing else), but instead we
simply pass a known good NaN instead.
Note that in the code removed there was a bug; the 64 bit mask for quiet
NaNs should have been
0x0008000000000000instead of the specified0x0001000000000000.