From 471b163ddf72cbe8991eb2b25bd06c57b8e966a5 Mon Sep 17 00:00:00 2001
From: Erik <erikdesjardins@users.noreply.github.com>
Date: Fri, 13 Jul 2018 16:04:30 -0400
Subject: [PATCH] implement trunc and truncf

---
 src/lib.rs                 |  4 ----
 src/math/mod.rs            |  4 ++++
 src/math/trunc.rs          | 24 ++++++++++++++++++++++++
 src/math/truncf.rs         | 24 ++++++++++++++++++++++++
 test-generator/src/main.rs |  4 ++--
 5 files changed, 54 insertions(+), 6 deletions(-)
 create mode 100644 src/math/trunc.rs
 create mode 100644 src/math/truncf.rs

diff --git a/src/lib.rs b/src/lib.rs
index ed163ff98..fa709ad75 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -44,7 +44,6 @@ pub trait F32Ext {
     #[cfg(todo)]
     fn round(self) -> Self;
 
-    #[cfg(todo)]
     fn trunc(self) -> Self;
 
     #[cfg(todo)]
@@ -163,7 +162,6 @@ impl F32Ext for f32 {
         roundf(self)
     }
 
-    #[cfg(todo)]
     #[inline]
     fn trunc(self) -> Self {
         truncf(self)
@@ -372,7 +370,6 @@ pub trait F64Ext {
 
     fn round(self) -> Self;
 
-    #[cfg(todo)]
     fn trunc(self) -> Self;
 
     #[cfg(todo)]
@@ -494,7 +491,6 @@ impl F64Ext for f64 {
         round(self)
     }
 
-    #[cfg(todo)]
     #[inline]
     fn trunc(self) -> Self {
         trunc(self)
diff --git a/src/math/mod.rs b/src/math/mod.rs
index e400badd1..71b58dda8 100644
--- a/src/math/mod.rs
+++ b/src/math/mod.rs
@@ -15,6 +15,8 @@ mod sqrtf;
 mod logf;
 mod expf;
 mod floor;
+mod trunc;
+mod truncf;
 
 //mod service;
 
@@ -30,6 +32,8 @@ pub use self::{
     logf::logf,
     expf::expf,
     floor::floor,
+    trunc::trunc,
+    truncf::truncf,
 };
 
 fn isnanf(x: f32) -> bool {
diff --git a/src/math/trunc.rs b/src/math/trunc.rs
new file mode 100644
index 000000000..b50ffd771
--- /dev/null
+++ b/src/math/trunc.rs
@@ -0,0 +1,24 @@
+use core::f64;
+
+#[inline]
+pub fn trunc(x: f64) -> f64 {
+    let x1p120 = f64::from_bits(0x4770000000000000); // 0x1p120f === 2 ^ 120
+
+    let mut i: u64 = x.to_bits();
+    let mut e: i64 = (i >> 52 & 0x7ff) as i64 - 0x3ff + 12;
+    let m: u64;
+
+    if e >= 52 + 12 {
+        return x;
+    }
+    if e < 12 {
+        e = 1;
+    }
+    m = -1i64 as u64 >> e;
+    if (i & m) == 0 {
+        return x;
+    }
+    force_eval!(x + x1p120);
+    i &= !m;
+    f64::from_bits(i)
+}
diff --git a/src/math/truncf.rs b/src/math/truncf.rs
new file mode 100644
index 000000000..f7d7249e3
--- /dev/null
+++ b/src/math/truncf.rs
@@ -0,0 +1,24 @@
+use core::f32;
+
+#[inline]
+pub fn truncf(x: f32) -> f32 {
+    let x1p120 = f32::from_bits(0x7b800000); // 0x1p120f === 2 ^ 120
+
+    let mut i: u32 = x.to_bits();
+    let mut e: i32 = (i >> 23 & 0xff) as i32 - 0x7f + 9;
+    let m: u32;
+
+    if e >= 23 + 9 {
+        return x;
+    }
+    if e < 9 {
+        e = 1;
+    }
+    m = -1i32 as u32 >> e;
+    if (i & m) == 0 {
+        return x;
+    }
+    force_eval!(x + x1p120);
+    i &= !m;
+    f32::from_bits(i)
+}
diff --git a/test-generator/src/main.rs b/test-generator/src/main.rs
index 42e157ad8..6353b257d 100644
--- a/test-generator/src/main.rs
+++ b/test-generator/src/main.rs
@@ -562,7 +562,7 @@ fn main() -> Result<(), Box<Error>> {
 f32_f32! {
     // acosf,
     // floorf,
-    // truncf
+    truncf,
     // asinf,
     // atanf,
     // cbrtf,
@@ -625,7 +625,7 @@ f64_f64! {
     // sqrt,
     // tan,
     // tanh,
-    // trunc,
+    trunc,
     fabs,
 }