implement floats by running the ops on the host architecture

src/interpreter/mod.rs

@@ -169,7 +169,8 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
     // TODO(solson): Try making const_to_primval instead.
     fn const_to_ptr(&mut self, const_val: &const_val::ConstVal) -> EvalResult<'tcx, Pointer> {
         use rustc::middle::const_val::ConstVal::*;
-        use rustc_const_math::{ConstInt, ConstIsize, ConstUsize};
+        use rustc_const_math::{ConstInt, ConstIsize, ConstUsize, ConstFloat};
+        use std::mem::transmute;
         macro_rules! i2p {
             ($i:ident, $n:expr) => {{
                 let ptr = self.memory.allocate($n);
@@ -178,7 +179,15 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
             }}
         }
         match *const_val {
-            Float(_f) => unimplemented!(),
+            Float(ConstFloat::F32(f)) => {
+                let i = unsafe { transmute::<_, u32>(f) };
+                i2p!(i, 4)
+            },
+            Float(ConstFloat::F64(f)) => {
+                let i = unsafe { transmute::<_, u64>(f) };
+                i2p!(i, 8)
+            },
+            Float(ConstFloat::FInfer{..}) => unreachable!(),
             Integral(ConstInt::Infer(_)) => unreachable!(),
             Integral(ConstInt::InferSigned(_)) => unreachable!(),
             Integral(ConstInt::I8(i)) => i2p!(i, 1),
@@ -824,7 +833,8 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
     }
 
     pub fn read_primval(&mut self, ptr: Pointer, ty: Ty<'tcx>) -> EvalResult<'tcx, PrimVal> {
-        use syntax::ast::{IntTy, UintTy};
+        use syntax::ast::{IntTy, UintTy, FloatTy};
+        use std::mem::transmute;
         let val = match (self.memory.pointer_size(), &ty.sty) {
             (_, &ty::TyBool)              => PrimVal::Bool(self.memory.read_bool(ptr)?),
             (_, &ty::TyChar)              => {
@@ -848,6 +858,14 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
             (_, &ty::TyUint(UintTy::U32)) => PrimVal::U32(self.memory.read_uint(ptr, 4)? as u32),
             (8, &ty::TyUint(UintTy::Us)) |
             (_, &ty::TyUint(UintTy::U64)) => PrimVal::U64(self.memory.read_uint(ptr, 8)? as u64),
+            (_, &ty::TyFloat(FloatTy::F32)) => {
+                let i = self.memory.read_uint(ptr, 4)? as u32;
+                PrimVal::F32(unsafe { transmute(i) })
+            },
+            (_, &ty::TyFloat(FloatTy::F64)) => {
+                let i = self.memory.read_uint(ptr, 8)?;
+                PrimVal::F64(unsafe { transmute(i) })
+            },
 
             (_, &ty::TyFnDef(def_id, substs, fn_ty)) => {
                 PrimVal::FnPtr(self.memory.create_fn_ptr(def_id, substs, fn_ty))

src/memory.rs

@@ -394,6 +394,7 @@ impl<'a, 'tcx> Memory<'a, 'tcx> {
     }
 
     pub fn write_primval(&mut self, ptr: Pointer, val: PrimVal) -> EvalResult<'tcx, ()> {
+        use std::mem::transmute;
         let pointer_size = self.pointer_size();
         match val {
             PrimVal::Bool(b) => self.write_bool(ptr, b),
@@ -407,6 +408,8 @@ impl<'a, 'tcx> Memory<'a, 'tcx> {
             PrimVal::U64(n)  => self.write_uint(ptr, n as u64, 8),
             PrimVal::Char(c) => self.write_uint(ptr, c as u64, 4),
             PrimVal::IntegerPtr(n) => self.write_uint(ptr, n as u64, pointer_size),
+            PrimVal::F32(f) => self.write_uint(ptr, unsafe { transmute::<_, u32>(f) } as u64, 4),
+            PrimVal::F64(f) => self.write_uint(ptr, unsafe { transmute::<_, u64>(f) }, 8),
             PrimVal::FnPtr(_p) |
             PrimVal::AbstractPtr(_p) => unimplemented!(),
         }

src/primval.rs

@@ -13,6 +13,8 @@ pub enum PrimVal {
     FnPtr(Pointer),
     IntegerPtr(u64),
     Char(char),
+
+    F32(f32), F64(f64),
 }
 
 /// returns the result of the operation and whether the operation overflowed
@@ -57,6 +59,34 @@ pub fn binary_op<'tcx>(bin_op: mir::BinOp, left: PrimVal, right: PrimVal) -> Eva
         })
     }
 
+    macro_rules! float_binops {
+        ($v:ident, $l:ident, $r:ident) => ({
+            match bin_op {
+                Add    => $v($l + $r),
+                Sub    => $v($l - $r),
+                Mul    => $v($l * $r),
+                Div    => $v($l / $r),
+                Rem    => $v($l % $r),
+
+                // invalid float ops
+                BitXor => unreachable!(),
+                BitAnd => unreachable!(),
+                BitOr  => unreachable!(),
+                Shl => unreachable!(),
+                Shr => unreachable!(),
+
+                // directly comparing floats is questionable
+                // miri could forbid it, or at least miri as rust const eval should forbid it
+                Eq => Bool($l == $r),
+                Ne => Bool($l != $r),
+                Lt => Bool($l < $r),
+                Le => Bool($l <= $r),
+                Gt => Bool($l > $r),
+                Ge => Bool($l >= $r),
+            }
+        })
+    }
+
     fn unrelated_ptr_ops<'tcx>(bin_op: mir::BinOp) -> EvalResult<'tcx, PrimVal> {
         use rustc::mir::repr::BinOp::*;
         match bin_op {
@@ -128,6 +158,8 @@ pub fn binary_op<'tcx>(bin_op: mir::BinOp, left: PrimVal, right: PrimVal) -> Eva
         (U16(l), U16(r)) => int_binops!(U16, l, r),
         (U32(l), U32(r)) => int_binops!(U32, l, r),
         (U64(l), U64(r)) => int_binops!(U64, l, r),
+        (F32(l), F32(r)) => float_binops!(F32, l, r),
+        (F64(l), F64(r)) => float_binops!(F64, l, r),
         (Char(l), Char(r)) => match bin_op {
             Eq => Bool(l == r),
             Ne => Bool(l != r),
@@ -211,6 +243,9 @@ pub fn unary_op<'tcx>(un_op: mir::UnOp, val: PrimVal) -> EvalResult<'tcx, PrimVa
         (Not, U16(n)) => Ok(U16(!n)),
         (Not, U32(n)) => Ok(U32(!n)),
         (Not, U64(n)) => Ok(U64(!n)),
+
+        (Neg, F64(n)) => Ok(F64(-n)),
+        (Neg, F32(n)) => Ok(F32(-n)),
         _ => Err(EvalError::Unimplemented(format!("unimplemented unary op: {:?}, {:?}", un_op, val))),
     }
 }

tests/run-pass/floats.rs

@@ -0,0 +1,8 @@
+
+fn main() {
+    assert_eq!(6.0_f32*6.0_f32, 36.0_f32);
+    assert_eq!(6.0_f64*6.0_f64, 36.0_f64);
+    assert_eq!(-{5.0_f32}, -5.0_f32);
+    assert!((5.0_f32/0.0).is_infinite());
+    assert!((-5.0_f32).sqrt().is_nan());
+}