Add implementations for f128 addition and subtraction

Author: tgross35

README.md

@@ -232,7 +232,7 @@ These builtins are needed to support 128-bit integers.
 
 These builtins are needed to support `f16` and `f128`, which are in the process of being added to Rust.
 
-- [ ] addtf3.c
+- [x] addtf3.c
 - [ ] comparetf2.c
 - [ ] divtf3.c
 - [x] extenddftf2.c
@@ -255,7 +255,7 @@ These builtins are needed to support `f16` and `f128`, which are in the process
 - [ ] ppc/fixunstfdi.c
 - [ ] ppc/floatditf.c
 - [ ] ppc/floatunditf.c
-- [ ] subtf3.c
+- [x] subtf3.c
 - [x] truncdfhf2.c
 - [x] truncsfhf2.c
 - [x] trunctfdf2.c

build.rs

@@ -479,9 +479,7 @@ mod c {
                 ("__floatsitf", "floatsitf.c"),
                 ("__floatunditf", "floatunditf.c"),
                 ("__floatunsitf", "floatunsitf.c"),
-                ("__addtf3", "addtf3.c"),
                 ("__multf3", "multf3.c"),
-                ("__subtf3", "subtf3.c"),
                 ("__divtf3", "divtf3.c"),
                 ("__powitf2", "powitf2.c"),
                 ("__fe_getround", "fp_mode.c"),
@@ -500,9 +498,7 @@ mod c {
         if target_arch == "mips64" {
             sources.extend(&[
                 ("__netf2", "comparetf2.c"),
-                ("__addtf3", "addtf3.c"),
                 ("__multf3", "multf3.c"),
-                ("__subtf3", "subtf3.c"),
                 ("__fixtfsi", "fixtfsi.c"),
                 ("__floatsitf", "floatsitf.c"),
                 ("__fixunstfsi", "fixunstfsi.c"),
@@ -515,9 +511,7 @@ mod c {
         if target_arch == "loongarch64" {
             sources.extend(&[
                 ("__netf2", "comparetf2.c"),
-                ("__addtf3", "addtf3.c"),
                 ("__multf3", "multf3.c"),
-                ("__subtf3", "subtf3.c"),
                 ("__fixtfsi", "fixtfsi.c"),
                 ("__floatsitf", "floatsitf.c"),
                 ("__fixunstfsi", "fixunstfsi.c"),

src/float/add.rs

@@ -203,6 +203,11 @@ intrinsics! {
         add(a, b)
     }
 
+    #[cfg(not(feature = "no-f16-f128"))]
+    pub extern "C" fn __addtf3(a: f128, b: f128) -> f128 {
+        add(a, b)
+    }
+
     #[cfg(target_arch = "arm")]
     pub extern "C" fn __addsf3vfp(a: f32, b: f32) -> f32 {
         a + b

src/float/sub.rs

@@ -15,6 +15,12 @@ intrinsics! {
         __adddf3(a, f64::from_repr(b.repr() ^ f64::SIGN_MASK))
     }
 
+    #[cfg(not(feature = "no-f16-f128"))]
+    pub extern "C" fn __subtf3(a: f128, b: f128) -> f128 {
+        use crate::float::add::__addtf3;
+        __addtf3(a, f128::from_repr(b.repr() ^ f128::SIGN_MASK))
+    }
+
     #[cfg(target_arch = "arm")]
     pub extern "C" fn __subsf3vfp(a: f32, b: f32) -> f32 {
         a - b

testcrate/Cargo.toml

@@ -33,3 +33,5 @@ no-asm = ["compiler_builtins/no-asm"]
 no-f16-f128 = ["compiler_builtins/no-f16-f128"]
 mem = ["compiler_builtins/mem"]
 mangled-names = ["compiler_builtins/mangled-names"]
+# Skip tests that rely on f128 symbols being available on the system
+no-sys-f128 = []

testcrate/build.rs

@@ -0,0 +1,18 @@
+use std::env;
+
+fn main() {
+    let target = env::var("TARGET").unwrap();
+
+    // These platforms do not have f128 symbols available in their system libraries, so
+    // skip related tests.
+    if target.starts_with("arm-")
+        || target.contains("apple-darwin")
+        || target.contains("windows-msvc")
+        // FIXME(llvm): There is an ABI incompatibility between GCC and Clang on 32-bit x86.
+        // See <https://github.com/llvm/llvm-project/issues/77401>.
+        || target.starts_with("i686")
+    {
+        println!("cargo:warning=using apfloat fallback for f128");
+        println!("cargo:rustc-cfg=feature=\"no-sys-f128\"");
+    }
+}

testcrate/tests/addsub.rs

@@ -1,4 +1,6 @@
 #![allow(unused_macros)]
+#![feature(f128)]
+#![feature(f16)]
 
 use core::ops::{Add, Sub};
 use testcrate::*;
@@ -109,6 +111,15 @@ fn float_addsub() {
         f32, __addsf3, __subsf3, Single, all();
         f64, __adddf3, __subdf3, Double, all();
     );
+
+    #[cfg(not(feature = "no-f16-f128"))]
+    {
+        use compiler_builtins::float::{add::__addtf3, sub::__subtf3, Float};
+
+        float_sum!(
+            f128, __addtf3, __subtf3, Quad, not(feature = "no-sys-f128");
+        );
+    }
 }
 
 #[cfg(target_arch = "arm")]