add gamma function shims

Author: RalfJung

src/tools/miri/src/lib.rs

@@ -1,4 +1,5 @@
 #![feature(rustc_private)]
+#![feature(float_gamma)]
 #![feature(map_try_insert)]
 #![feature(never_type)]
 #![feature(try_blocks)]

src/tools/miri/src/shims/foreign_items.rs

@@ -815,6 +815,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
             | "atanf"
             | "log1pf"
             | "expm1f"
+            | "tgammaf"
             => {
                 let [f] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                 // FIXME: Using host floats.
@@ -830,6 +831,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                     "atanf" => f.atan(),
                     "log1pf" => f.ln_1p(),
                     "expm1f" => f.exp_m1(),
+                    "tgammaf" => f.gamma(),
                     _ => bug!(),
                 };
                 this.write_scalar(Scalar::from_u32(res.to_bits()), dest)?;
@@ -866,6 +868,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
             | "atan"
             | "log1p"
             | "expm1"
+            | "tgamma"
             => {
                 let [f] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
                 // FIXME: Using host floats.
@@ -881,6 +884,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                     "atan" => f.atan(),
                     "log1p" => f.ln_1p(),
                     "expm1" => f.exp_m1(),
+                    "tgamma" => f.gamma(),
                     _ => bug!(),
                 };
                 this.write_scalar(Scalar::from_u64(res.to_bits()), dest)?;
@@ -917,6 +921,26 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                 let res = x.scalbn(exp);
                 this.write_scalar(Scalar::from_f64(res), dest)?;
             }
+            "lgammaf_r" => {
+                let [x, signp] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
+                // FIXME: Using host floats.
+                let x = f32::from_bits(this.read_scalar(x)?.to_u32()?);
+                let signp = this.deref_pointer(signp)?;
+
+                let (res, sign) = x.ln_gamma();
+                this.write_int(sign, &signp)?;
+                this.write_scalar(Scalar::from_u32(res.to_bits()), dest)?;
+            }
+            "lgamma_r" => {
+                let [x, signp] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
+                // FIXME: Using host floats.
+                let x = f64::from_bits(this.read_scalar(x)?.to_u64()?);
+                let signp = this.deref_pointer(signp)?;
+
+                let (res, sign) = x.ln_gamma();
+                this.write_int(sign, &signp)?;
+                this.write_scalar(Scalar::from_u64(res.to_bits()), dest)?;
+            }
 
             // Architecture-specific shims
             "llvm.x86.addcarry.64" if this.tcx.sess.target.arch == "x86_64" => {

src/tools/miri/tests/pass/intrinsics-math.rs

@@ -1,5 +1,4 @@
-// SPDX-License-Identifier: MIT OR Apache-2.0
-// SPDX-FileCopyrightText: The Rust Project Developers (see https://thanks.rust-lang.org)
+#![feature(float_gamma)]
 
 macro_rules! assert_approx_eq {
     ($a:expr, $b:expr) => {{
@@ -130,4 +129,20 @@ pub fn main() {
     );
     assert_approx_eq!(0.5f32.atanh(), 0.54930614433405484569762261846126285f32);
     assert_approx_eq!(0.5f64.atanh(), 0.54930614433405484569762261846126285f64);
+
+    assert_approx_eq!(5.0f32.gamma(), 24.0);
+    assert_approx_eq!(5.0f64.gamma(), 24.0);
+    // These fail even on the host, precision seems to be terrible.
+    //assert_approx_eq!(-0.5f32.gamma(), -2.0 * f32::consts::PI.sqrt());
+    //assert_approx_eq!(-0.5f64.gamma(), -2.0 * f64::consts::PI.sqrt());
+
+    assert_eq!(2.0f32.ln_gamma(), (0.0, 1));
+    assert_eq!(2.0f64.ln_gamma(), (0.0, 1));
+    // Gamma(-0.5) = -2*sqrt(π)
+    let (val, sign) = (-0.5f32).ln_gamma();
+    assert_approx_eq!(val, (2.0 * f32::consts::PI.sqrt()).ln());
+    assert_eq!(sign, -1);
+    let (val, sign) = (-0.5f64).ln_gamma();
+    assert_approx_eq!(val, (2.0 * f64::consts::PI.sqrt()).ln());
+    assert_eq!(sign, -1);
 }