1 //! Android ABI-compatibility module
2 //!
3 //! The ABI of Android has changed quite a bit over time, and std attempts to be
4 //! both forwards and backwards compatible as much as possible. We want to
5 //! always work with the most recent version of Android, but we also want to
6 //! work with older versions of Android for whenever projects need to.
7 //!
8 //! Our current minimum supported Android version is `android-9`, e.g., Android
9 //! with API level 9. We then in theory want to work on that and all future
10 //! versions of Android!
11 //!
12 //! Some of the detection here is done at runtime via `dlopen` and
13 //! introspection. Other times no detection is performed at all and we just
14 //! provide a fallback implementation as some versions of Android we support
15 //! don't have the function.
16 //!
17 //! You'll find more details below about why each compatibility shim is needed.
18
19 #![cfg(target_os = "android")]
20
21 use dlibc::{c_int, sighandler_t};
22
23 use super::weak::weak;
24
25 // The `log2` and `log2f` functions apparently appeared in android-18, or at
26 // least you can see they're not present in the android-17 header [1] and they
27 // are present in android-18 [2].
28 //
29 // [1]: https://chromium.googlesource.com/android_tools/+/20ee6d20/ndk/platforms
30 // /android-17/arch-arm/usr/include/math.h
31 // [2]: https://chromium.googlesource.com/android_tools/+/20ee6d20/ndk/platforms
32 // /android-18/arch-arm/usr/include/math.h
33 //
34 // Note that these shims are likely less precise than directly calling `log2`,
35 // but hopefully that should be enough for now...
36 //
37 // Note that mathematically, for any arbitrary `y`:
38 //
39 // log_2(x) = log_y(x) / log_y(2)
40 // = log_y(x) / (1 / log_2(y))
41 // = log_y(x) * log_2(y)
42 //
43 // Hence because `ln` (log_e) is available on all Android we just choose `y = e`
44 // and get:
45 //
46 // log_2(x) = ln(x) * log_2(e)
47
48 #[cfg(not(test))]
log2f32(f: f32) -> f3249 pub fn log2f32(f: f32) -> f32 {
50 f.ln() * crate::std::f32::consts::LOG2_E
51 }
52
53 #[cfg(not(test))]
log2f64(f: f64) -> f6454 pub fn log2f64(f: f64) -> f64 {
55 f.ln() * crate::std::f64::consts::LOG2_E
56 }
57
58 // Back in the day [1] the `signal` function was just an inline wrapper
59 // around `bsd_signal`, but starting in API level android-20 the `signal`
60 // symbols was introduced [2]. Finally, in android-21 the API `bsd_signal` was
61 // removed [3].
62 //
63 // Basically this means that if we want to be binary compatible with multiple
64 // Android releases (oldest being 9 and newest being 21) then we need to check
65 // for both symbols and not actually link against either.
66 //
67 // [1]: https://chromium.googlesource.com/android_tools/+/20ee6d20/ndk/platforms
68 // /android-18/arch-arm/usr/include/signal.h
69 // [2]: https://chromium.googlesource.com/android_tools/+/fbd420/ndk_experimental
70 // /platforms/android-20/arch-arm
71 // /usr/include/signal.h
72 // [3]: https://chromium.googlesource.com/android_tools/+/20ee6d/ndk/platforms
73 // /android-21/arch-arm/usr/include/signal.h
signal(signum: c_int, handler: sighandler_t) -> sighandler_t74 pub unsafe fn signal(signum: c_int, handler: sighandler_t) -> sighandler_t {
75 weak!(fn signal(c_int, sighandler_t) -> sighandler_t);
76 weak!(fn bsd_signal(c_int, sighandler_t) -> sighandler_t);
77
78 let f = signal.get().or_else(|| bsd_signal.get());
79 let f = f.expect("neither `signal` nor `bsd_signal` symbols found");
80 f(signum, handler)
81 }
82