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Diffstat (limited to 'library/std/src/sys/unix/android.rs')
| -rw-r--r-- | library/std/src/sys/unix/android.rs | 81 |
1 files changed, 81 insertions, 0 deletions
diff --git a/library/std/src/sys/unix/android.rs b/library/std/src/sys/unix/android.rs new file mode 100644 index 000000000..73ff10ab8 --- /dev/null +++ b/library/std/src/sys/unix/android.rs @@ -0,0 +1,81 @@ +//! Android ABI-compatibility module +//! +//! The ABI of Android has changed quite a bit over time, and libstd attempts to +//! be both forwards and backwards compatible as much as possible. We want to +//! always work with the most recent version of Android, but we also want to +//! work with older versions of Android for whenever projects need to. +//! +//! Our current minimum supported Android version is `android-9`, e.g., Android +//! with API level 9. We then in theory want to work on that and all future +//! versions of Android! +//! +//! Some of the detection here is done at runtime via `dlopen` and +//! introspection. Other times no detection is performed at all and we just +//! provide a fallback implementation as some versions of Android we support +//! don't have the function. +//! +//! You'll find more details below about why each compatibility shim is needed. + +#![cfg(target_os = "android")] + +use libc::{c_int, sighandler_t}; + +use super::weak::weak; + +// The `log2` and `log2f` functions apparently appeared in android-18, or at +// least you can see they're not present in the android-17 header [1] and they +// are present in android-18 [2]. +// +// [1]: https://chromium.googlesource.com/android_tools/+/20ee6d20/ndk/platforms +// /android-17/arch-arm/usr/include/math.h +// [2]: https://chromium.googlesource.com/android_tools/+/20ee6d20/ndk/platforms +// /android-18/arch-arm/usr/include/math.h +// +// Note that these shims are likely less precise than directly calling `log2`, +// but hopefully that should be enough for now... +// +// Note that mathematically, for any arbitrary `y`: +// +// log_2(x) = log_y(x) / log_y(2) +// = log_y(x) / (1 / log_2(y)) +// = log_y(x) * log_2(y) +// +// Hence because `ln` (log_e) is available on all Android we just choose `y = e` +// and get: +// +// log_2(x) = ln(x) * log_2(e) + +#[cfg(not(test))] +pub fn log2f32(f: f32) -> f32 { + f.ln() * crate::f32::consts::LOG2_E +} + +#[cfg(not(test))] +pub fn log2f64(f: f64) -> f64 { + f.ln() * crate::f64::consts::LOG2_E +} + +// Back in the day [1] the `signal` function was just an inline wrapper +// around `bsd_signal`, but starting in API level android-20 the `signal` +// symbols was introduced [2]. Finally, in android-21 the API `bsd_signal` was +// removed [3]. +// +// Basically this means that if we want to be binary compatible with multiple +// Android releases (oldest being 9 and newest being 21) then we need to check +// for both symbols and not actually link against either. +// +// [1]: https://chromium.googlesource.com/android_tools/+/20ee6d20/ndk/platforms +// /android-18/arch-arm/usr/include/signal.h +// [2]: https://chromium.googlesource.com/android_tools/+/fbd420/ndk_experimental +// /platforms/android-20/arch-arm +// /usr/include/signal.h +// [3]: https://chromium.googlesource.com/android_tools/+/20ee6d/ndk/platforms +// /android-21/arch-arm/usr/include/signal.h +pub unsafe fn signal(signum: c_int, handler: sighandler_t) -> sighandler_t { + weak!(fn signal(c_int, sighandler_t) -> sighandler_t); + weak!(fn bsd_signal(c_int, sighandler_t) -> sighandler_t); + + let f = signal.get().or_else(|| bsd_signal.get()); + let f = f.expect("neither `signal` nor `bsd_signal` symbols found"); + f(signum, handler) +} |