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[bigint] Fix tie-to-even case in BigInt::ToNumber

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Bug: v8:6791, v8:7506
Change-Id: I8ff41cb5fab03ab2ced8f21016a0744582a3fcee
Reviewed-on: https://chromium-review.googlesource.com/942387
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51666}
This commit is contained in:
Jakob Kummerow 2018-03-01 11:01:43 -08:00 committed by Commit Bot
parent 67fa841bcb
commit dcbcf0469d
2 changed files with 16 additions and 2 deletions
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3
src/objects/bigint.cc
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@ -977,7 +977,8 @@ MutableBigInt::Rounding MutableBigInt::DecideRounding(Handle<BigIntBase> x,
// If any other remaining bit is set, round up.
bitmask -= 1;
if ((current_digit & bitmask) != 0) return kRoundUp;
for (; digit_index >= 0; digit_index--) {
while (digit_index > 0) {
digit_index--;
if (x->digit(digit_index) != 0) return kRoundUp;
}
return kTie;

15
test/mjsunit/harmony/bigint/tonumber.js
View File

@ -5,7 +5,7 @@
// Flags: --harmony-bigint
function Check(bigint, number_string) {
var number = Number(number_string);
var number = Number(bigint);
if (number_string.substring(0, 2) === "0x") {
assertEquals(number_string.substring(2), number.toString(16));
} else {
@ -29,6 +29,19 @@ Check(0x7ffffffffffffdn, "0x7ffffffffffffc"); // 55 bits, rounding down.
Check(0x7ffffffffffffen, "0x80000000000000"); // 55 bits, tie to even.
Check(0x7fffffffffffffn, "0x80000000000000"); // 55 bits, rounding up.
Check(0x1ffff0000ffff0000n, "0x1ffff0000ffff0000"); // 65 bits.
Check(100000000000000008192n, "100000000000000000000"); // Tie to even.
// Check the cornercase where the most significant cut-off bit is 1.
// If a digit beyond the mantissa is non-zero, we must round up;
// otherwise tie to even.
// ...digit2 ][ digit1 ][ digit0 ]
// [ mantissa ]
Check(0x01000000000000080000000000000000001000n,
"0x1000000000000100000000000000000000000");
Check(0x01000000000000080000000000000000000000n,
"0x1000000000000000000000000000000000000");
Check(0x01000000000000180000000000000000000000n,
"0x1000000000000200000000000000000000000");
// Values near infinity.
Check(1n << 1024n, "Infinity");