Merge rust-lang/libm#79

79: implement ceil r=japaric a=lucasmarqs

closes rust-lang/libm#53 

Co-authored-by: Lucas Marques <lucas.smarques@outlook.com>
Co-authored-by: Jorge Aparicio <jorge@japaric.io>

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

@@ -347,7 +347,6 @@ impl F32Ext for f32 {
 pub trait F64Ext: private::Sealed {
     fn floor(self) -> Self;
 
-    #[cfg(todo)]
     fn ceil(self) -> Self;
 
     fn round(self) -> Self;
@@ -455,7 +454,6 @@ impl F64Ext for f64 {
         floor(self)
     }
 
-    #[cfg(todo)]
     #[inline]
     fn ceil(self) -> Self {
         ceil(self)

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

@@ -0,0 +1,39 @@
+use core::f64;
+
+const TOINT: f64 = 1. / f64::EPSILON;
+
+#[inline]
+pub fn ceil(x: f64) -> f64 {
+    let u: u64 = x.to_bits();
+    let e: i64 = (u >> 52 & 0x7ff) as i64;
+    let y: f64;
+
+    if e >= 0x3ff + 52 || x == 0. {
+        return x;
+    }
+    // y = int(x) - x, where int(x) is an integer neighbor of x
+    y = if (u >> 63) != 0 {
+        x - TOINT + TOINT - x
+    } else {
+        x + TOINT - TOINT - x
+    };
+    // special case because of non-nearest rounding modes
+    if e <= 0x3ff - 1 {
+        force_eval!(y);
+        return if (u >> 63) != 0 { -0. } else { 1. };
+    }
+    if y < 0. {
+        x + y + 1.
+    } else {
+        x + y
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn sanity_check() {
+        assert_eq!(super::ceil(1.1), 2.0);
+        assert_eq!(super::ceil(2.9), 3.0);
+    }
+}

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

@@ -6,6 +6,7 @@ macro_rules! force_eval {
     };
 }
 
+mod ceil;
 mod ceilf;
 mod cosf;
 mod expf;
@@ -35,6 +36,7 @@ mod trunc;
 mod truncf;
 
 // Use separated imports instead of {}-grouped imports for easier merging.
+pub use self::ceil::ceil;
 pub use self::ceilf::ceilf;
 pub use self::cosf::cosf;
 pub use self::expf::expf;

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

@@ -700,7 +700,7 @@ f64_f64! {
     // asin,
     // atan,
     // cbrt,
-    // ceil,
+    ceil,
     // cos,
     // cosh,
     // exp,