test/mjsunit/unbox-double-arrays.js

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// Test dictionary -> double elements -> dictionary elements round trip

var foo = new Array(500000);

function func(a) {
  for (var i= 0; i < 100000; ++i ) {
    a[i] = i+0.5;
  }
}

func(foo);

for (var i= 0; i < 100000; i += 500 ) {
  assertEquals(i+0.5, foo[i]);
}

delete foo[5];
// Don't use assertEquals for comparison to undefined due to
assertTrue(undefined === foo[5]);
assertTrue(undefined === foo[500000-1]);
assertTrue(undefined === foo[-1]);
assertEquals(500000, foo.length);

// Cause the array to grow beyond it's JSArray length. This will double the
// size of the capacity and force the array into "slow" dictionary case.
foo[500001] = 50;
assertEquals(50, foo[500001]);
assertEquals(500002, foo.length);
assertTrue(undefined === foo[5])
assertTrue(undefined === foo[500000-1])
assertTrue(undefined === foo[-1])
assertEquals(500002, foo.length);

// Test dictionary -> double elements -> fast elements.

var foo2 = new Array(500000);
func(foo2);
delete foo2[5];

// Convert back to fast elements and make sure the contents of the array are
// unchanged.
foo2[25] = new Object();
for (var i= 0; i < 100000; i += 500 ) {
  if (i != 25 && i != 5) {
    assertEquals(i+0.5, foo2[i]);
  }
}
assertTrue(undefined === foo2[5])
assertTrue(undefined === foo2[500000-1])
assertTrue(undefined === foo2[-1])
assertEquals(500000, foo2.length);