feat: 实现 JsValue NaN-Boxing 值类型

crates/oxide_vm/src/lib.rs

@@ -1 +1,4 @@
 #![doc = "OxideJS - Register-based VM with epoch arena memory"]
+
+pub mod value;
+pub use value::JsValue;

crates/oxide_vm/src/value.rs

@@ -0,0 +1,174 @@
+use std::fmt;
+
+/// Quiet NaN prefix — bits 63-51 = sign(1) + exponent(0x7FF) + quiet_bit(1)
+const QNAN_PREFIX: u64 = 0xFFF8_0000_0000_0000;
+
+/// NaN exponent mask — bits 62-52
+const EXP_MASK: u64 = 0x7FF0_0000_0000_0000;
+
+/// Mantissa mask — bits 51-0
+const MANTISSA_MASK: u64 = 0x000F_FFFF_FFFF_FFFF;
+
+/// Tag sits in bits 50-48 of mantissa
+const TAG_MASK: u64 = 0x0007_0000_0000_0000;
+const TAG_SHIFT: u64 = 48;
+const TAG_INT: u64 = 0;
+const TAG_BOOL: u64 = 1;
+const TAG_NULL: u64 = 2;
+const TAG_UNDEFINED: u64 = 3;
+const TAG_OBJECT: u64 = 4;
+
+/// 48-bit pointer mask (x86-64 canonical VA)
+const PTR_MASK: u64 = 0x0000_FFFF_FFFF_FFFF;
+
+/// 32-bit integer payload mask
+const INT_MASK: u64 = 0x0000_0000_FFFF_FFFF;
+
+fn make_tag(tag: u64) -> u64 {
+    QNAN_PREFIX | (tag << TAG_SHIFT)
+}
+
+fn get_tag(bits: u64) -> u64 {
+    (bits & TAG_MASK) >> TAG_SHIFT
+}
+
+#[repr(transparent)]
+#[derive(Copy, Clone, PartialEq)]
+pub struct JsValue(u64);
+
+impl JsValue {
+    pub fn int(v: i32) -> Self {
+        Self(make_tag(TAG_INT) | (v as u32 as u64))
+    }
+
+    pub fn float(v: f64) -> Self {
+        let bits = v.to_bits();
+        if is_nan_bits(bits) {
+            Self(QNAN_PREFIX | 1)
+        } else {
+            Self(bits)
+        }
+    }
+
+    pub fn bool(v: bool) -> Self {
+        Self(make_tag(TAG_BOOL) | (v as u64))
+    }
+
+    pub fn null() -> Self {
+        Self(make_tag(TAG_NULL))
+    }
+
+    pub fn undefined() -> Self {
+        Self(make_tag(TAG_UNDEFINED))
+    }
+
+    pub fn object(ptr: *const u8) -> Self {
+        let addr = ptr as u64;
+        debug_assert!(addr <= PTR_MASK, "object pointer must fit in 48 bits");
+        Self(make_tag(TAG_OBJECT) | addr)
+    }
+
+    pub fn is_double(&self) -> bool {
+        !is_nan_bits(self.0)
+    }
+
+    pub fn is_int(&self) -> bool {
+        get_tag(self.0) == TAG_INT
+    }
+
+    pub fn is_bool(&self) -> bool {
+        get_tag(self.0) == TAG_BOOL
+    }
+
+    pub fn is_null(&self) -> bool {
+        self.0 == make_tag(TAG_NULL)
+    }
+
+    pub fn is_undefined(&self) -> bool {
+        self.0 == make_tag(TAG_UNDEFINED)
+    }
+
+    pub fn is_object(&self) -> bool {
+        get_tag(self.0) == TAG_OBJECT
+    }
+
+    pub fn as_double(&self) -> f64 {
+        debug_assert!(self.is_double(), "JsValue is not a double");
+        f64::from_bits(self.0)
+    }
+
+    pub fn as_int(&self) -> i32 {
+        debug_assert!(self.is_int(), "JsValue is not an int");
+        (self.0 & INT_MASK) as i32
+    }
+
+    pub fn as_bool(&self) -> bool {
+        debug_assert!(self.is_bool(), "JsValue is not a bool");
+        (self.0 & 1) != 0
+    }
+
+    pub fn as_ptr(&self) -> *const u8 {
+        debug_assert!(self.is_object(), "JsValue is not an object");
+        (self.0 & PTR_MASK) as *const u8
+    }
+}
+
+fn is_nan_bits(bits: u64) -> bool {
+    (bits & EXP_MASK) == EXP_MASK && (bits & MANTISSA_MASK) != 0
+}
+
+impl fmt::Display for JsValue {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if self.is_int() {
+            write!(f, "{}", self.as_int())
+        } else if self.is_double() {
+            let d = self.as_double();
+            if d.is_nan() {
+                write!(f, "NaN")
+            } else if d.is_infinite() {
+                if d.is_sign_positive() {
+                    write!(f, "Infinity")
+                } else {
+                    write!(f, "-Infinity")
+                }
+            } else {
+                write!(f, "{d}")
+            }
+        } else if self.is_bool() {
+            write!(f, "{}", self.as_bool())
+        } else if self.is_null() {
+            write!(f, "null")
+        } else if self.is_undefined() {
+            write!(f, "undefined")
+        } else if self.is_object() {
+            write!(f, "{{object}}")
+        } else {
+            write!(f, "{{unknown}}")
+        }
+    }
+}
+
+impl fmt::Debug for JsValue {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if self.is_int() {
+            write!(f, "JsValue(Int({}))", self.as_int())
+        } else if self.is_double() {
+            let d = self.as_double();
+            if d.is_nan() {
+                write!(f, "JsValue(Double(NaN))")
+            } else {
+                write!(f, "JsValue(Double({d}))")
+            }
+        } else if self.is_bool() {
+            write!(f, "JsValue(Bool({}))", self.as_bool())
+        } else if self.is_null() {
+            write!(f, "JsValue(Null)")
+        } else if self.is_undefined() {
+            write!(f, "JsValue(Undefined)")
+        } else if self.is_object() {
+            write!(f, "JsValue(Object({:p}))", self.as_ptr())
+        } else {
+            write!(f, "JsValue(Unknown)")
+        }
+    }
+}