share sqrt implemention across float types

Author: RalfJung

src/intrinsics/math.rs

@@ -1,12 +1,26 @@
 use rand::Rng;
-use rustc_apfloat::{self, Float, Round};
+use rustc_apfloat::{self, Float, FloatConvert, Round};
 use rustc_middle::mir;
 use rustc_middle::ty::{self, FloatTy};
 
 use self::helpers::{ToHost, ToSoft};
 use super::check_intrinsic_arg_count;
 use crate::*;
 
+fn sqrt<'tcx, F: Float + FloatConvert<F> + Into<Scalar>>(
+    this: &mut MiriInterpCx<'tcx>,
+    args: &[OpTy<'tcx>],
+    dest: &MPlaceTy<'tcx>,
+) -> InterpResult<'tcx> {
+    let [f] = check_intrinsic_arg_count(args)?;
+    let f = this.read_scalar(f)?;
+    let f: F = f.to_float()?;
+    // Sqrt is specified to be fully precise.
+    let res = math::sqrt(f);
+    let res = this.adjust_nan(res, &[f]);
+    this.write_scalar(res, dest)
+}
+
 impl<'tcx> EvalContextExt<'tcx> for crate::MiriInterpCx<'tcx> {}
 pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
     fn emulate_math_intrinsic(
@@ -20,38 +34,10 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 
         match intrinsic_name {
             // Operations we can do with soft-floats.
-            "sqrtf16" => {
-                let [f] = check_intrinsic_arg_count(args)?;
-                let f = this.read_scalar(f)?.to_f16()?;
-                // Sqrt is specified to be fully precise.
-                let res = math::sqrt(f);
-                let res = this.adjust_nan(res, &[f]);
-                this.write_scalar(res, dest)?;
-            }
-            "sqrtf32" => {
-                let [f] = check_intrinsic_arg_count(args)?;
-                let f = this.read_scalar(f)?.to_f32()?;
-                // Sqrt is specified to be fully precise.
-                let res = math::sqrt(f);
-                let res = this.adjust_nan(res, &[f]);
-                this.write_scalar(res, dest)?;
-            }
-            "sqrtf64" => {
-                let [f] = check_intrinsic_arg_count(args)?;
-                let f = this.read_scalar(f)?.to_f64()?;
-                // Sqrt is specified to be fully precise.
-                let res = math::sqrt(f);
-                let res = this.adjust_nan(res, &[f]);
-                this.write_scalar(res, dest)?;
-            }
-            "sqrtf128" => {
-                let [f] = check_intrinsic_arg_count(args)?;
-                let f = this.read_scalar(f)?.to_f128()?;
-                // Sqrt is specified to be fully precise.
-                let res = math::sqrt(f);
-                let res = this.adjust_nan(res, &[f]);
-                this.write_scalar(res, dest)?;
-            }
+            "sqrtf16" => sqrt::<rustc_apfloat::ieee::Half>(this, args, dest)?,
+            "sqrtf32" => sqrt::<rustc_apfloat::ieee::Single>(this, args, dest)?,
+            "sqrtf64" => sqrt::<rustc_apfloat::ieee::Double>(this, args, dest)?,
+            "sqrtf128" => sqrt::<rustc_apfloat::ieee::Quad>(this, args, dest)?,
 
             "fmaf32" => {
                 let [a, b, c] = check_intrinsic_arg_count(args)?;

src/math.rs

@@ -2,7 +2,7 @@ use std::ops::Neg;
 use std::{f32, f64};
 
 use rand::Rng as _;
-use rustc_apfloat::Float as _;
+use rustc_apfloat::Float;
 use rustc_apfloat::ieee::{DoubleS, IeeeFloat, Semantics, SingleS};
 use rustc_middle::ty::{self, FloatTy, ScalarInt};
 
@@ -317,19 +317,19 @@ where
     }
 }
 
-pub(crate) fn sqrt<S: rustc_apfloat::ieee::Semantics>(x: IeeeFloat<S>) -> IeeeFloat<S> {
+pub(crate) fn sqrt<F: Float>(x: F) -> F {
     match x.category() {
         // preserve zero sign
         rustc_apfloat::Category::Zero => x,
         // propagate NaN
         rustc_apfloat::Category::NaN => x,
         // sqrt of negative number is NaN
-        _ if x.is_negative() => IeeeFloat::NAN,
+        _ if x.is_negative() => F::NAN,
         // sqrt(∞) = ∞
-        rustc_apfloat::Category::Infinity => IeeeFloat::INFINITY,
+        rustc_apfloat::Category::Infinity => F::INFINITY,
         rustc_apfloat::Category::Normal => {
             // Floating point precision, excluding the integer bit
-            let prec = i32::try_from(S::PRECISION).unwrap() - 1;
+            let prec = i32::try_from(F::PRECISION).unwrap() - 1;
 
             // x = 2^(exp - prec) * mant
             // where mant is an integer with prec+1 bits
@@ -394,7 +394,7 @@ pub(crate) fn sqrt<S: rustc_apfloat::ieee::Semantics>(x: IeeeFloat<S>) -> IeeeFl
             res = (res + 1) >> 1;
 
             // Build resulting value with res as mantissa and exp/2 as exponent
-            IeeeFloat::from_u128(res).value.scalbn(exp / 2 - prec)
+            F::from_u128(res).value.scalbn(exp / 2 - prec)
         }
     }
 }