diff --git a/library/compiler-builtins/libm/src/lib.rs b/library/compiler-builtins/libm/src/lib.rs
index e51a7c2dc489..9f4365712d65 100644
--- a/library/compiler-builtins/libm/src/lib.rs
+++ b/library/compiler-builtins/libm/src/lib.rs
@@ -44,7 +44,6 @@ pub trait F32Ext {
     #[cfg(todo)]
     fn round(self) -> Self;
 
-    #[cfg(todo)]
     fn trunc(self) -> Self;
 
     #[cfg(todo)]
@@ -162,7 +161,6 @@ impl F32Ext for f32 {
         roundf(self)
     }
 
-    #[cfg(todo)]
     #[inline]
     fn trunc(self) -> Self {
         truncf(self)
@@ -370,7 +368,6 @@ pub trait F64Ext {
 
     fn round(self) -> Self;
 
-    #[cfg(todo)]
     fn trunc(self) -> Self;
 
     #[cfg(todo)]
@@ -492,7 +489,6 @@ impl F64Ext for f64 {
         round(self)
     }
 
-    #[cfg(todo)]
     #[inline]
     fn trunc(self) -> Self {
         trunc(self)
diff --git a/library/compiler-builtins/libm/src/math/mod.rs b/library/compiler-builtins/libm/src/math/mod.rs
index bc69aca0f61d..76092c2eb117 100644
--- a/library/compiler-builtins/libm/src/math/mod.rs
+++ b/library/compiler-builtins/libm/src/math/mod.rs
@@ -16,6 +16,8 @@ mod logf;
 mod expf;
 mod floor;
 mod cosf;
+mod trunc;
+mod truncf;
 
 mod service;
 
@@ -32,6 +34,8 @@ pub use self::{
     expf::expf,
     floor::floor,
     cosf::cosf,
+    trunc::trunc,
+    truncf::truncf,
 };
 
 fn isnanf(x: f32) -> bool {
diff --git a/library/compiler-builtins/libm/src/math/trunc.rs b/library/compiler-builtins/libm/src/math/trunc.rs
new file mode 100644
index 000000000000..b50ffd77156a
--- /dev/null
+++ b/library/compiler-builtins/libm/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/library/compiler-builtins/libm/src/math/truncf.rs b/library/compiler-builtins/libm/src/math/truncf.rs
new file mode 100644
index 000000000000..f7d7249e3519
--- /dev/null
+++ b/library/compiler-builtins/libm/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/library/compiler-builtins/libm/test-generator/src/main.rs b/library/compiler-builtins/libm/test-generator/src/main.rs
index 42e157ad8768..6353b257dce3 100644
--- a/library/compiler-builtins/libm/test-generator/src/main.rs
+++ b/library/compiler-builtins/libm/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,
 }