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Improve double-to-ulong conversion tests

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#KT-27108
This commit is contained in:
Ilya Gorbunov
2019-02-14 17:22:26 +03:00
parent 892fb9f39e
commit 908009bf42
1 changed files with 18 additions and 11 deletions
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libraries/stdlib/test/unsigned/ULongTest.kt
+18 -11
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@@ -119,6 +119,7 @@ class ULongTest {
val float = Long.MAX_VALUE.toFloat() + long.toFloat() // We lose accuracy here, hence `eps` is used. val float = Long.MAX_VALUE.toFloat() + long.toFloat() // We lose accuracy here, hence `eps` is used.
val ulong = Long.MAX_VALUE.toULong() + long.toULong() val ulong = Long.MAX_VALUE.toULong() + long.toULong()
// TODO: replace with ulp comparison when available on Float
val eps = 1e+13 val eps = 1e+13
assertTrue(abs(float - ulong.toFloat()) < eps) assertTrue(abs(float - ulong.toFloat()) < eps)
} }
@@ -141,11 +142,12 @@ class ULongTest {
repeat(100) { repeat(100) {
val long = Random.nextLong(from = 0, until = Long.MAX_VALUE) val long = Random.nextLong(from = 0, until = Long.MAX_VALUE)
val double = Long.MAX_VALUE.toDouble() + long.toDouble() // We lose accuracy here, hence `eps` is used. val value = Long.MAX_VALUE.toULong() + long.toULong()
val ulong = Long.MAX_VALUE.toULong() + long.toULong() val expected = Long.MAX_VALUE.toDouble() + long.toDouble() // Should be accurate to one ulp
val actual = value.toDouble()
val diff = abs(expected - value.toDouble())
val eps = 1e+4 assertTrue(diff <= actual.ulp, "$actual should be within one ulp (${actual.ulp}) from the expected $expected")
assertTrue(abs(double - ulong.toDouble()) < eps)
} }
fun testRounding(from: ULong, count: UInt) { fun testRounding(from: ULong, count: UInt) {
@@ -208,14 +210,11 @@ class ULongTest {
} }
repeat(100) { repeat(100) {
val diff = Random.nextDouble() * Long.MAX_VALUE val d = 2.0.pow(63) * (1 + Random.nextDouble())
val d = Long.MAX_VALUE.toDouble() + diff val expected = specialDoubleToULong(d)
val ul = Long.MAX_VALUE.toULong() + diff.toLong().toULong() val actual = d.toULong()
val eps = 1e-6
assertTrue(d.toULong() / ul <= 1u) assertEquals(expected, actual, "Expected bit pattern: ${expected.toString(2)}, actual bit pattern: ${actual.toString(2)}")
assertTrue(d / ul.toDouble() < 1 + eps)
assertTrue(d / ul.toDouble() > 1 - eps)
} }
fun testTrailingBits(v: Double, count: Int) { fun testTrailingBits(v: Double, count: Int) {
@@ -241,4 +240,12 @@ class ULongTest {
testTrailingBits(v, msb - 52) testTrailingBits(v, msb - 52)
} }
} }
/** Creates an ULong value directly from mantissa bits of Double that is in range [2^63, 2^64). */
private fun specialDoubleToULong(v: Double): ULong {
require(v >= 2.0.pow(63))
require(v < 2.0.pow(64))
val bits = v.toBits().toULong()
return (1uL shl 63) + ((bits and (1uL shl 52) - 1u) shl 11)
}
} }