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<!DOCTYPE html>
<title>Test exponentialRampToValueAtTime() with a moderate ratio of change</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script>
'use strict';
promise_test(async function() {
const bufferSize = 128;
const sampleRate = 16384;
// 3 * 2^6, not a power of two, so that there is some rounding error in the
// exponent
const rampEndSample = 192;
// These values are chosen so that there is rounding error in
// (offset1/offset0)^(1/rampEndSample).
const offset0 = 4.;
const offset1 = 7.;
// 8 units in the last place (ulp) is a generous tolerance if single
// precision powf() is used. Math.pow(2, -23) ~ 1 ulp.
// A simple recurrence relation formulation with only single precision
// arithmetic applied across the whole rendering quantum would accumulate
// error up to 50 ulp, losing 5.6 of the 24 bits of precision.
const relativeTolerance = 8 * Math.pow(2, -23);
const context = new OfflineAudioContext(1, bufferSize, sampleRate);
const source = new ConstantSourceNode(context);
source.start();
// Explicit event to work around
// https://bugzilla.mozilla.org/show_bug.cgi?id=1265393
source.offset.setValueAtTime(offset0, 0.);
source.offset.exponentialRampToValueAtTime(offset1, rampEndSample/sampleRate);
source.connect(context.destination);
const buffer = await context.startRendering();
assert_equals(buffer.length, bufferSize, "output buffer length");
const output = buffer.getChannelData(0);
const ratio = offset1 / offset0;
for (let i = 0; i < bufferSize; ++i) {
// Math.pow() uses double precision, while `output` has single precision,
// but `tolerance` is more than enough to accommodate differences.
const expected = offset0 * Math.pow(offset1/offset0, i/rampEndSample);
assert_approx_equals(
output[i],
expected,
relativeTolerance * expected,
"scheduled value at " + i);
}
});
</script>
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