1 files changed, 81 insertions, 0 deletions
diff --git a/library/core/src/num/diy_float.rs b/library/core/src/num/diy_float.rs
new file mode 100644
index 000000000..ce7f6475d
--- /dev/null
+++ b/library/core/src/num/diy_float.rs
@@ -0,0 +1,81 @@
+//! Extended precision "soft float", for internal use only.
+
+// This module is only for dec2flt and flt2dec, and only public because of coretests.
+// It is not intended to ever be stabilized.
+#![doc(hidden)]
+#![unstable(
+    feature = "core_private_diy_float",
+    reason = "internal routines only exposed for testing",
+    issue = "none"
+)]
+
+/// A custom 64-bit floating point type, representing `f * 2^e`.
+#[derive(Copy, Clone, Debug)]
+#[doc(hidden)]
+pub struct Fp {
+    /// The integer mantissa.
+    pub f: u64,
+    /// The exponent in base 2.
+    pub e: i16,
+}
+
+impl Fp {
+    /// Returns a correctly rounded product of itself and `other`.
+    pub fn mul(&self, other: &Fp) -> Fp {
+        const MASK: u64 = 0xffffffff;
+        let a = self.f >> 32;
+        let b = self.f & MASK;
+        let c = other.f >> 32;
+        let d = other.f & MASK;
+        let ac = a * c;
+        let bc = b * c;
+        let ad = a * d;
+        let bd = b * d;
+        let tmp = (bd >> 32) + (ad & MASK) + (bc & MASK) + (1 << 31) /* round */;
+        let f = ac + (ad >> 32) + (bc >> 32) + (tmp >> 32);
+        let e = self.e + other.e + 64;
+        Fp { f, e }
+    }
+
+    /// Normalizes itself so that the resulting mantissa is at least `2^63`.
+    pub fn normalize(&self) -> Fp {
+        let mut f = self.f;
+        let mut e = self.e;
+        if f >> (64 - 32) == 0 {
+            f <<= 32;
+            e -= 32;
+        }
+        if f >> (64 - 16) == 0 {
+            f <<= 16;
+            e -= 16;
+        }
+        if f >> (64 - 8) == 0 {
+            f <<= 8;
+            e -= 8;
+        }
+        if f >> (64 - 4) == 0 {
+            f <<= 4;
+            e -= 4;
+        }
+        if f >> (64 - 2) == 0 {
+            f <<= 2;
+            e -= 2;
+        }
+        if f >> (64 - 1) == 0 {
+            f <<= 1;
+            e -= 1;
+        }
+        debug_assert!(f >= (1 << 63));
+        Fp { f, e }
+    }
+
+    /// Normalizes itself to have the shared exponent.
+    /// It can only decrease the exponent (and thus increase the mantissa).
+    pub fn normalize_to(&self, e: i16) -> Fp {
+        let edelta = self.e - e;
+        assert!(edelta >= 0);
+        let edelta = edelta as usize;
+        assert_eq!(self.f << edelta >> edelta, self.f);
+        Fp { f: self.f << edelta, e }
+    }
+}