From 6cb02c31fbf95201438cbe658e981f9b6385c837 Mon Sep 17 00:00:00 2001
From: y21 <30553356+y21@users.noreply.github.com>
Date: Sat, 17 Feb 2024 15:53:33 +0100
Subject: [PATCH] specialize interning `f64`s that fit in a usize

---
 crates/dash_vm/src/js_std/number.rs   | 10 +++++-----
 crates/dash_vm/src/util.rs            | 21 +++++++++++++++------
 crates/dash_vm/src/value/primitive.rs |  4 ++--
 3 files changed, 22 insertions(+), 13 deletions(-)

diff --git a/crates/dash_vm/src/js_std/number.rs b/crates/dash_vm/src/js_std/number.rs
index a021c1a3..e78f5227 100644
--- a/crates/dash_vm/src/js_std/number.rs
+++ b/crates/dash_vm/src/js_std/number.rs
@@ -1,5 +1,5 @@
 use crate::throw;
-use crate::util::format_f64;
+use crate::util::intern_f64;
 use crate::value::function::native::CallContext;
 use crate::value::ops::conversions::ValueConversion;
 use crate::value::primitive::{Number, MAX_SAFE_INTEGERF};
@@ -30,13 +30,13 @@ pub fn to_string(cx: CallContext) -> Result<Value, Value> {
     };
 
     let re = match radix {
-        2 => format!("{:b}", num as u64),
-        10 => format_f64(num),
-        16 => format!("{:x}", num as u64),
+        2 => cx.scope.intern(format!("{:b}", num as u64).as_ref()),
+        10 => intern_f64(cx.scope, num),
+        16 => cx.scope.intern(format!("{:x}", num as u64)),
         _ => throw!(cx.scope, RangeError, "Invalid radix: {}", radix),
     };
 
-    Ok(Value::String(cx.scope.intern(re.as_ref()).into()))
+    Ok(Value::String(re.into()))
 }
 
 pub fn is_finite(cx: CallContext) -> Result<Value, Value> {
diff --git a/crates/dash_vm/src/util.rs b/crates/dash_vm/src/util.rs
index 8b6e7f94..48cdf67f 100644
--- a/crates/dash_vm/src/util.rs
+++ b/crates/dash_vm/src/util.rs
@@ -1,5 +1,9 @@
 use std::num::FpCategory;
 
+use dash_middle::interner::{sym, Symbol};
+
+use crate::localscope::LocalScope;
+
 /// Marks the code path leading to this call as cold, or "unlikely"
 #[cold]
 pub fn cold_path() {}
@@ -19,11 +23,16 @@ pub trait Captures<'a> {}
 
 impl<'a, T: ?Sized> Captures<'a> for T {}
 
-pub fn format_f64(n: f64) -> String {
-    // TODO: specialize zero, infinity, NaN by "interning" them in vm.statics
+pub fn intern_f64(sc: &mut LocalScope, n: f64) -> Symbol {
+    if n.trunc() == n && n >= 0.0 && n <= usize::MAX as f64 {
+        // Happy path: no fractional part and fits in a usize
+        // This can use the specialized usize interner
+        return sc.intern_usize(n as usize);
+    }
+
     match n.classify() {
-        FpCategory::Infinite => "Infinity".into(),
-        FpCategory::Nan => "NaN".into(),
+        FpCategory::Infinite => sym::Infinity,
+        FpCategory::Nan => sym::NaN,
         _ if n >= 1e21f64 || n <= -1e21f64 => {
             let mut digits = 0;
             let mut n = n;
@@ -35,8 +44,8 @@ pub fn format_f64(n: f64) -> String {
                 n /= 10f64;
                 digits += 1;
             }
-            format!("{n:.0}e+{digits}")
+            sc.intern(format!("{n:.0}e+{digits}").as_ref())
         }
-        _ => format!("{n}"),
+        _ => sc.intern(n.to_string().as_ref()),
     }
 }
diff --git a/crates/dash_vm/src/value/primitive.rs b/crates/dash_vm/src/value/primitive.rs
index 652ef52e..a313c49e 100644
--- a/crates/dash_vm/src/value/primitive.rs
+++ b/crates/dash_vm/src/value/primitive.rs
@@ -9,7 +9,7 @@ use crate::gc::handle::Handle;
 use crate::gc::interner::sym;
 use crate::localscope::LocalScope;
 use crate::throw;
-use crate::util::{format_f64, Captures};
+use crate::util::{intern_f64, Captures};
 
 use super::boxed::{Boolean as BoxedBoolean, Number as BoxedNumber, Symbol as BoxedSymbol};
 use super::object::{Object, PropertyKey, PropertyValue};
@@ -481,7 +481,7 @@ impl ValueConversion for f64 {
     }
 
     fn to_js_string(&self, sc: &mut LocalScope) -> Result<JsString, Value> {
-        Ok(sc.intern(format_f64(*self).as_ref()).into())
+        Ok(intern_f64(sc, *self).into())
     }
 
     fn length_of_array_like(&self, _sc: &mut LocalScope) -> Result<usize, Value> {