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// The data representations of values of different types are given below.
// - Pointers are 64 bit unsigned (positive) ints which are
// word-aligned, i.e. 0 mod 8. All types not listed below are
// allocated on the heap behind a pointer.
// - Int:
// < 63-bit signed int > 1
// Ints are a 63 bit int with a 1 in the low bit.
// - Booleans and nil are 2 mod 8:
// - False is 0x2
// - True is 0xA
// - Nil is 0x12
// - A symbol's low byte is 0x4, and the high 56 bytes are an unsigned integer constant
// representing a pointer into the symbol table.
//
// n.b. 6 mod 8 is unused.
#[derive(PartialEq, Eq, Debug, Hash, Clone, Copy)]
pub struct Pointer(pub usize);
impl Pointer {
pub fn offset(self, i: i64) -> Self {
let Pointer(u) = self;
if i > 0 {
return Pointer(u + usize::try_from(i).unwrap());
}
return Pointer(u - usize::try_from(-i).unwrap());
}
}
#[derive(PartialEq, Eq, Debug, Clone, Copy)]
pub struct Value(pub u64);
impl Value {
pub fn is_nil(self) -> bool {
let Value(stack_representation) = self;
return stack_representation == 0;
}
pub fn is_pointer(self) -> bool {
let Value(stack_representation) = self;
return stack_representation & 0x7 == 0;
}
pub fn from_pointer(p: Pointer) -> Self {
let Pointer(x) = p;
return Value(u64::try_from(x).unwrap());
}
pub fn to_pointer(self) -> Result<Pointer, String> {
let Value(stack_representation) = self;
if !self.is_pointer() {
return Err(format!("value {:x} is not a pointer", stack_representation));
}
return Ok(Pointer(usize::try_from(stack_representation).unwrap()));
}
pub fn is_int(self) -> bool {
let Value(stack_representation) = self;
return stack_representation & 0x1 == 1;
}
pub fn from_int(i: i64) -> Self {
return Value((i as u64) << 1 | 1);
}
pub fn to_int(self) -> Result<i64, String> {
let Value(stack_representation) = self;
if !self.is_int() {
return Err(format!("value {:x} is not an int", stack_representation));
}
return Ok(stack_representation as i64 >> 1);
}
pub fn is_bool(self) -> bool {
let Value(stack_representation) = self;
return stack_representation == 0xa || stack_representation == 0x2;
}
pub fn from_bool(b: bool) -> Self {
if b {
return Value(0xa);
}
return Value(0x2);
}
pub fn to_bool(self) -> Result<bool, String> {
let Value(stack_representation) = self;
if !self.is_bool() {
return Err(format!("value {:x} is not a boolean", stack_representation));
}
return Ok(stack_representation == 0xa);
}
pub fn is_char(self) -> bool {
let Value(stack_representation) = self;
return stack_representation & 0x7 == 4;
}
pub fn from_char(c: char) -> Self {
return Value(u64::from(c) << 32 | 0x4);
}
pub fn to_char(self) -> Result<char, String> {
let Value(stack_representation) = self;
if !self.is_char() {
return Err(format!("value {:x} is not a char", stack_representation));
}
return Ok(
char::from_u32((stack_representation >> 32) as u32).ok_or(format!(
"value {:x} is not a valid char",
stack_representation >> 32
))?,
);
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn is_nil() {
assert_eq!(true, Value(0).is_nil());
}
#[test]
fn is_not_nil() {
assert_eq!(false, Value(1).is_nil());
}
#[test]
fn is_pointer() {
assert_eq!(true, Value(0xf8).is_pointer());
}
#[test]
fn is_not_pointer() {
assert_eq!(false, Value(1).is_pointer());
}
#[test]
fn from_pointer() {
assert_eq!(Value(0xf8), Value::from_pointer(Pointer(0xf8)));
}
#[test]
fn to_pointer() {
assert_eq!(Ok(Pointer(0xf8)), Value(0xf8).to_pointer());
}
#[test]
fn is_int() {
assert_eq!(true, Value(1).is_int());
}
#[test]
fn is_not_int() {
assert_eq!(false, Value(0).is_int());
}
#[test]
fn from_int() {
assert_eq!(Value(0xb), Value::from_int(5));
}
#[test]
fn to_int() {
assert_eq!(Ok(5), Value(0xb).to_int());
}
#[test]
fn true_is_bool() {
assert_eq!(true, Value(0xa).is_bool());
}
#[test]
fn false_is_bool() {
assert_eq!(true, Value(2).is_bool());
}
#[test]
fn is_not_bool() {
assert_eq!(false, Value(0).is_bool());
}
#[test]
fn true_from_bool() {
assert_eq!(Value(0xa), Value::from_bool(true));
}
#[test]
fn false_from_bool() {
assert_eq!(Value(2), Value::from_bool(false));
}
#[test]
fn true_to_bool() {
assert_eq!(Ok(true), Value(0xa).to_bool());
}
#[test]
fn false_to_bool() {
assert_eq!(Ok(false), Value(2).to_bool());
}
#[test]
fn is_char() {
assert_eq!(true, Value(0x6100000004).is_char());
}
#[test]
fn is_not_char() {
assert_eq!(false, Value(0).is_char());
}
#[test]
fn from_char() {
assert_eq!(Value(0x5800000004), Value::from_char('X'));
}
#[test]
fn to_char() {
assert_eq!(Ok('😂'), Value(0x1f60200000004).to_char());
}
}
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