From bc94c70687c467d7fa4c655b90033de99d27211c Mon Sep 17 00:00:00 2001
From: Joseph Ryan <josephryan3.14@gmail.com>
Date: Fri, 13 Jul 2018 20:46:09 -0500
Subject: [PATCH] implement roundf

---
 library/compiler-builtins/libm/src/lib.rs     |  2 --
 .../compiler-builtins/libm/src/math/mod.rs    |  8 +++--
 .../compiler-builtins/libm/src/math/roundf.rs | 33 +++++++++++++++++++
 .../libm/test-generator/src/main.rs           |  2 +-
 4 files changed, 40 insertions(+), 5 deletions(-)
 create mode 100644 library/compiler-builtins/libm/src/math/roundf.rs

diff --git a/library/compiler-builtins/libm/src/lib.rs b/library/compiler-builtins/libm/src/lib.rs
index 0d13590c7ecc..b87e82b2ac6a 100644
--- a/library/compiler-builtins/libm/src/lib.rs
+++ b/library/compiler-builtins/libm/src/lib.rs
@@ -41,7 +41,6 @@ pub trait F32Ext {
     #[cfg(todo)]
     fn ceil(self) -> Self;
 
-    #[cfg(todo)]
     fn round(self) -> Self;
 
     #[cfg(todo)]
@@ -160,7 +159,6 @@ impl F32Ext for f32 {
         ceilf(self)
     }
 
-    #[cfg(todo)]
     #[inline]
     fn round(self) -> Self {
         roundf(self)
diff --git a/library/compiler-builtins/libm/src/math/mod.rs b/library/compiler-builtins/libm/src/math/mod.rs
index 41359bf8c059..8032bdabf9ac 100644
--- a/library/compiler-builtins/libm/src/math/mod.rs
+++ b/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 scalbnf;
 mod sqrtf;
 
@@ -17,6 +20,7 @@ pub use self::fabsf::fabsf;
 pub use self::fmodf::fmodf;
 pub use self::powf::powf;
 pub use self::round::round;
+pub use self::roundf::roundf;
 pub use self::scalbnf::scalbnf;
 pub use self::sqrtf::sqrtf;
 
diff --git a/library/compiler-builtins/libm/src/math/roundf.rs b/library/compiler-builtins/libm/src/math/roundf.rs
new file mode 100644
index 000000000000..bd2488fa99c8
--- /dev/null
+++ b/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
+    }
+}
diff --git a/library/compiler-builtins/libm/test-generator/src/main.rs b/library/compiler-builtins/libm/test-generator/src/main.rs
index 5ff78ffc8b37..2f78a8ed38da 100644
--- a/library/compiler-builtins/libm/test-generator/src/main.rs
+++ b/library/compiler-builtins/libm/test-generator/src/main.rs
@@ -574,7 +574,7 @@ f32_f32! {
     // fdimf,
     // log10f,
     // log2f,
-    // roundf,
+    roundf,
     // sinf,
     // sinhf,
     // tanf,