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// Lowering provides a specialisation when the base operand is a constant which
// is a power of two.
//
// Test bailout conditions for this optimisation.
function test(x) {
function pow(x, y) { return `Math.pow(${x}, ${y})` };
function exp(x, y) { return `((${x}) ** ${y})` };
function make(fn) {
return Function("y, z", `
// Load from array to prevent constant-folding.
// (Ion is currently not smart enough to realise that both array
// values are the same.)
var ys = [y, y];
var zs = [z, z];
for (var i = 0; i < 1000; ++i) {
assertEq(${fn(x, "ys[i & 1]")}, zs[i & 1]);
}
`);
}
function double(v) {
// NB: numberToDouble() always returns a double value.
return numberToDouble(v);
}
// Find the first power which will exceed the Int32 range by computing ⌈log_x(2 ^ 31)⌉.
var limit = Math.ceil(Math.log2(2 ** 31) / Math.log2(x));
assertEq(Math.pow(x, limit - 1) < 2 ** 31, true);
assertEq(Math.pow(x, limit) >= 2 ** 31, true);
function* args(first, last) {
// Run the test function a few times without a bailout.
for (var i = 0; i < 3; ++i) {
yield first;
}
// |last| should trigger a bailout.
yield last;
}
// Test precision loss when the result exceeds 2**31.
for (var fn of [make(pow), make(exp)]) {
for (var y of args(limit - 1, limit)) {
// Ensure the callee always sees a double to avoid an early Bailout_ArgumentCheck.
var z = double(Math.pow(x, y));
fn(y, z);
}
}
// Test precision loss when the result is a fractional number.
for (var fn of [make(pow), make(exp)]) {
for (var y of args(0, -1)) {
// Ensure the callee always sees a double to avoid an early Bailout_ArgumentCheck.
var z = double(Math.pow(x, y));
fn(y, z);
}
}
// Find the first negative power which can be represented as a double
var negLimit = -Math.floor(1074 / Math.log2(x));
// Test precision loss when the result is a non-zero, fractional number.
for (var fn of [make(pow), make(exp)]) {
for (var y of args(limit - 1, limit)) {
// Ensure the callee always sees a double to avoid an early Bailout_ArgumentCheck.
var z = double(Math.pow(x, y));
fn(y, z);
}
}
}
function* range(a, b, fn) {
for (var i = a; i <= b; ++i) {
yield fn(i);
}
}
// Only 2^i with |i| ∈ {1..8} currently triggers the optimisation, but also test
// the next power-of-two values.
for (var x of range(1, 10, i => 2 ** i)) {
test(x);
}