std: Add compatibility with android-9 #33211
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r? @brson (rust_highfive has picked a reviewer for you, use r? to override) |
| // but hopefully that should be enough for now... | ||
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| pub fn log2f32(f: f32) -> f32 { | ||
| f.ln() / 2.0f32.ln() |
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ln(2) can be precalculated and its value put into a constant to be as accurate as possible. I doubt the compiler does that for us (and certainly doesn’t in the debug builds).
Here’s a way more than enough digits of ln(2) to cover f64:
0.6931471805599453094172321214581765680755001343602552541206800094933936219696947156058633269964186875420014810205...
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Perhaps std::f64::consts::LN_2 might help.
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Even better, instead of dividing by std::f64::consts::LN_2 it would be possible to multiply by std::f64::consts::LOG2_E
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I doubt the compiler does that for us (and certainly doesn’t in the debug builds).
FWIW, it does in release builds (using one of the constants is nicer of course).
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FWIW, it does in release builds (using one of the constants is nicer of course).
Might not do it in the cross-compiling case, since I think it actually uses the host's (!) libm to do the calculation, which isn't necessarily valid in the cross-compiling case.
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LGTM once the two comments are resolved. |
alexcrichton
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⌛ Testing commit 0be64f3 with merge 33ec2aa... |
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💔 Test failed - auto-linux-64-x-android-t |
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⌛ Testing commit 0e4ff0a with merge f25455d... |
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💔 Test failed - auto-linux-64-x-android-t |
The Gecko folks currently use Android API level 9 for their builds, so they're requesting that we move back our minimum supported API level from 18 to 9. Turns out, ABI-wise at least, there's not that many changes we need to take care of. The `ftruncate64` API appeared in android-12 and the `log2` and `log2f` APIs appeared in android-18. We can have a simple shim for `ftruncate64` which falls back on `ftruncate` and the `log2` function can be approximated with just `ln(f) / ln(2)`. This should at least get the standard library building on API level 9, although the tests aren't quite happening there just yet. As we seem to be growing a number of Android compatibility shims, they're now centralized in a common `sys::android` module.
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std: Add compatibility with android-9 The Gecko folks currently use Android API level 9 for their builds, so they're requesting that we move back our minimum supported API level from 18 to 9. Turns out, ABI-wise at least, there's not that many changes we need to take care of. The `ftruncate64` API appeared in android-12 and the `log2` and `log2f` APIs appeared in android-18. We can have a simple shim for `ftruncate64` which falls back on `ftruncate` and the `log2` function can be approximated with just `ln(f) / ln(2)`. This should at least get the standard library building on API level 9, although the tests aren't quite happening there just yet. As we seem to be growing a number of Android compatibility shims, they're now centralized in a common `sys::android` module.
The Gecko folks currently use Android API level 9 for their builds, so they're
requesting that we move back our minimum supported API level from 18 to 9. Turns
out, ABI-wise at least, there's not that many changes we need to take care of.
The
ftruncate64API appeared in android-12 and thelog2andlog2fAPIsappeared in android-18. We can have a simple shim for
ftruncate64which fallsback on
ftruncateand thelog2function can be approximated with justln(f) / ln(2).This should at least get the standard library building on API level 9, although
the tests aren't quite happening there just yet. As we seem to be growing a
number of Android compatibility shims, they're now centralized in a common
sys::androidmodule.