walt-compiler
Version:
Alternative syntax for WebAssembly text format
79 lines (77 loc) • 2.32 kB
JavaScript
/**
* Unary operator plugin.
*
* @flow
*/
import Syntax from 'walt-syntax';
import type { SemanticPlugin } from '../flow/types';
const shifts = {
i64: 63,
f64: 63,
i32: 31,
f32: 31,
};
const masks = {
i64: '0xffffffffffff',
f64: '0xffffffffffff',
i32: '0xffffff',
f32: '0xffffff',
};
// Unary expressions need to be patched so that the LHS type matches the RHS
export default function(): SemanticPlugin {
return {
semantics({ stmt }) {
return {
[Syntax.UnaryExpression]: _ignore => (args, transform) => {
const [unaryNode, context] = args;
// While it's counter-intuitive that an unary operation would have two operands
// it is simpler to always parse them as pseudo-binary and then simplify them here.
const [lhs, rhs] = unaryNode.params.map(p => transform([p, context]));
switch (unaryNode.value) {
// Transform bang
case '!':
const shift = shifts[lhs.type];
return transform([
stmt`(((${lhs} >> ${shift}) | ((~${lhs} + 1) >> ${shift})) + 1);`,
context,
]);
case '~':
const mask = masks[transform([lhs, context]).type];
return transform([stmt`(${lhs} ^ ${mask});`, context]);
case '-':
// Fold negation into a single opcode (a negative constant).
// The parser _currently_ generates 0 - <const> node pairs instead
if (rhs.Type === Syntax.Constant) {
return {
...rhs,
meta: {
...rhs.meta,
// Hint for generator
SIGN: -1,
},
};
}
// fallthrough
// eslint-disable-next-line
default:
return transform([
{
...unaryNode,
type: rhs.type,
params: [
{
...lhs,
type: rhs.type,
},
rhs,
],
Type: Syntax.BinaryExpression,
},
context,
]);
}
},
};
},
};
}