Merge rust-lang/libm#74

74: Implement roundf r=japaric a=P1n3appl3

closes rust-lang/libm#32 

Co-authored-by: Joseph Ryan <josephryan3.14@gmail.com>

library/compiler-builtins/libm/src/lib.rs

@@ -40,7 +40,6 @@ pub trait F32Ext: private::Sealed {
     #[cfg(todo)]
     fn ceil(self) -> Self;
 
-    #[cfg(todo)]
     fn round(self) -> Self;
 
     fn trunc(self) -> Self;
@@ -154,7 +153,6 @@ impl F32Ext for f32 {
         ceilf(self)
     }
 
-    #[cfg(todo)]
     #[inline]
     fn round(self) -> Self {
         roundf(self)

library/compiler-builtins/libm/src/math/mod.rs

@@ -1,7 +1,9 @@
 macro_rules! force_eval {
     ($e:expr) => {
-        unsafe { ::core::ptr::read_volatile(&$e); }
-    }
+        unsafe {
+            ::core::ptr::read_volatile(&$e);
+        }
+    };
 }
 
 mod fabs;
@@ -9,6 +11,7 @@ mod fabsf;
 mod fmodf;
 mod powf;
 mod round;
+mod roundf;
 mod scalbn;
 mod scalbnf;
 mod sqrt;
@@ -29,6 +32,7 @@ pub use self::{
     fmodf::fmodf,
     powf::powf,
     round::round,
+    roundf::roundf,
     scalbn::scalbn,
     scalbnf::scalbnf,
     sqrt::sqrt,

library/compiler-builtins/libm/src/math/roundf.rs

@@ -0,0 +1,33 @@
+use core::f32;
+
+const TOINT: f32 = 1.0 / f32::EPSILON;
+
+pub fn roundf(mut x: f32) -> f32 {
+    let i = x.to_bits();
+    let e: u32 = i >> 23 & 0xff;
+    let mut y: f32;
+
+    if e >= 0x7f + 23 {
+        return x;
+    }
+    if i >> 31 != 0 {
+        x = -x;
+    }
+    if e < 0x7f - 1 {
+        force_eval!(x + TOINT);
+        return 0.0 * x;
+    }
+    y = x + TOINT - TOINT - x;
+    if y > 0.5f32 {
+        y = y + x - 1.0;
+    } else if y <= -0.5f32 {
+        y = y + x + 1.0;
+    } else {
+        y = y + x;
+    }
+    if i >> 31 != 0 {
+        -y
+    } else {
+        y
+    }
+}

library/compiler-builtins/libm/test-generator/src/main.rs

@@ -666,7 +666,7 @@ f32_f32! {
     // log10f,
     // log2f,
     logf,
-    // roundf,
+    roundf,
     // sinf,
     // sinhf,
     // tanf,