Add support for f128 integer exponentiation

Adds `__powitf2`

Author: tgross35

README.md

@@ -250,7 +250,7 @@ These builtins are needed to support `f16` and `f128`, which are in the process
 - [ ] floatunditf.c
 - [ ] floatunsitf.c
 - [x] multf3.c
-- [ ] powitf2.c
+- [x] powitf2.c
 - [ ] ppc/fixtfdi.c
 - [ ] ppc/fixunstfdi.c
 - [ ] ppc/floatditf.c

build.rs

@@ -538,7 +538,6 @@ mod c {
                 ("__floatunditf", "floatunditf.c"),
                 ("__floatunsitf", "floatunsitf.c"),
                 ("__divtf3", "divtf3.c"),
-                ("__powitf2", "powitf2.c"),
                 ("__fe_getround", "fp_mode.c"),
                 ("__fe_raise_inexact", "fp_mode.c"),
             ]);

src/float/pow.rs

@@ -35,4 +35,16 @@ intrinsics! {
     pub extern "C" fn __powidf2(a: f64, b: i32) -> f64 {
         pow(a, b)
     }
+
+    #[avr_skip]
+    #[cfg(not(any(feature = "no-f16-f128", target_arch = "powerpc", target_arch = "powerpc64")))]
+    pub extern "C" fn __powitf2(a: f128, b: i32) -> f128 {
+        pow(a, b)
+    }
+
+    #[avr_skip]
+    #[cfg(all(not(feature = "no-f16-f128"), any(target_arch = "powerpc", target_arch = "powerpc64")))]
+    pub extern "C" fn __powikf2(a: f128, b: i32) -> f128 {
+        pow(a, b)
+    }
 }

testcrate/tests/misc.rs

@@ -1,5 +1,6 @@
 // makes configuration easier
 #![allow(unused_macros)]
+#![feature(f128)]
 
 use testcrate::*;
 
@@ -122,12 +123,15 @@ macro_rules! pow {
                                 b < $tolerance
                             } else {
                                 let quo = b / a;
-                                (quo < (1. + $tolerance)) && (quo > (1. - $tolerance))
+                                // FIXME(f16_f128): we do this to block const eval which currently
+                                // ICEs on f128. Change this once it works correctly.
+                                (quo < (1. + black_box($tolerance)))
+                                    && (quo > (1. - black_box($tolerance)))
                             }
                         };
                         if !good {
                             panic!(
-                                "{}({}, {}): std: {}, builtins: {}",
+                                "{}({:?}, {:?}): std: {:?}, builtins: {:?}",
                                 stringify!($fn), x, n, tmp0, tmp1
                             );
                         }
@@ -142,8 +146,32 @@ macro_rules! pow {
 mod float_pow {
     use super::*;
 
+    fn black_box<T>(val: T) -> T {
+        val
+    }
+
     pow! {
         f32, 1e-4, __powisf2;
         f64, 1e-12, __powidf2;
     }
 }
+
+#[cfg(not(all(target_arch = "x86", not(target_feature = "sse"))))]
+#[cfg(not(any(feature = "no-f16-f128", feature = "no-sys-f128")))]
+mod float_pow_f128 {
+    use super::*;
+    use core::hint::black_box;
+
+    // Windows can't link the required arithmetic functions. See
+    // <https://github.com/rust-lang/compiler-builtins/pull/614#issuecomment-2118636613>
+    #[cfg(not(target_family = "windows"))]
+    #[cfg(not(any(target_arch = "powerpc", target_arch = "powerpc64")))]
+    pow! {
+        f128, 1e-36, __powitf2;
+    }
+
+    #[cfg(any(target_arch = "powerpc", target_arch = "powerpc64"))]
+    pow! {
+        f128, 1e-36, __powikf2;
+    }
+}