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function toCharCodes(str) {
return [...str].map(s => s.length === 1 ? [s.charCodeAt(0)] : [s.charCodeAt(0), s.charCodeAt(1)])
.flat();
}
function test() {
// [Ascii; Latin-1, non-Ascii; non-Latin-1; non-BMP]
const constant = "AaÁáĀā𝐀𝐚";
const charCodes = toCharCodes(constant);
// Create a linear, but non-constant string with the same contents.
const linear = String.fromCharCode(...charCodes);
assertEq(linear, constant);
// Optimisation applies for |MCharCodeAt(MFromCharCode(MCharCodeAt(str, idx)), 0|.
for (let i = 0; i < 500; ++i) {
let idx = i & 3;
// str[idx] is compiled to |MFromCharCode(MCharCodeAt(str, idx))|.
assertEq(constant[idx].charCodeAt(0), charCodes[idx]);
assertEq(linear[idx].charCodeAt(0), charCodes[idx]);
// str.charAt(idx) is compiled to |MFromCharCode(MCharCodeAt(str, idx))|.
assertEq(constant.charAt(idx).charCodeAt(0), charCodes[idx]);
assertEq(linear.charAt(idx).charCodeAt(0), charCodes[idx]);
}
}
for (let i = 0; i < 4; ++i) {
test();
}
function testNonConstantIndex() {
// [Ascii; Latin-1, non-Ascii; non-Latin-1; non-BMP]
const constant = "AaÁáĀā𝐀𝐚";
const charCodes = toCharCodes(constant);
// Create a linear, but non-constant string with the same contents.
const linear = String.fromCharCode(...charCodes);
assertEq(linear, constant);
// No optimisation when the index isn't a constant zero.
let indices = [0, 1, 2, 3];
for (let i = 0; i < 500; ++i) {
let idx = i & 3;
// Always zero, but too complicated to infer at compile time.
let zero = indices[idx] - idx;
assertEq(constant[idx].charCodeAt(zero), charCodes[idx]);
assertEq(linear[idx].charCodeAt(zero), charCodes[idx]);
assertEq(constant.charAt(idx).charCodeAt(zero), charCodes[idx]);
assertEq(linear.charAt(idx).charCodeAt(zero), charCodes[idx]);
}
}
for (let i = 0; i < 4; ++i) {
testNonConstantIndex();
}
function testOOB() {
// [Ascii; Latin-1, non-Ascii; non-Latin-1; non-BMP]
const constant = "AaÁáĀā𝐀𝐚";
const charCodes = toCharCodes(constant);
// Create a linear, but non-constant string with the same contents.
const linear = String.fromCharCode(...charCodes);
assertEq(linear, constant);
// No optimisation when the index is out-of-bounds.
for (let i = 0; i < 500; ++i) {
let idx = i & 3;
assertEq(constant[idx].charCodeAt(1), NaN);
assertEq(linear[idx].charCodeAt(1), NaN);
assertEq(constant.charAt(idx).charCodeAt(1), NaN);
assertEq(linear.charAt(idx).charCodeAt(1), NaN);
}
}
for (let i = 0; i < 4; ++i) {
testOOB();
}
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