v8/test/mjsunit/harmony/bigint/tonumber.js

// Copyright 2017 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

function Check(bigint, number_string) {
  var number = Number(bigint);
  if (number_string.substring(0, 2) === "0x") {
    assertEquals(number_string.substring(2), number.toString(16));
  } else {
    assertEquals(number_string, number.toString());
  }
}

// Values in Smi range.
Check(0n, "0");
Check(1n, "1");
Check(-1n, "-1");

// Values in double range.
Check(12345678912n, "12345678912");
Check(-12345678912345n, "-12345678912345");
Check(0xfffffffffffffn, "0xfffffffffffff");    // 52 bits.
Check(0x1fffffffffffffn, "0x1fffffffffffff");  // 53 bits.
Check(0x3fffffffffffffn, "0x40000000000000");  // 54 bits, rounding up.
Check(0x3ffffffffffffen, "0x3ffffffffffffe");  // 54 bits, rounding down.
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");
Check(-1n << 1024n, "-Infinity");
Check(1n << 1023n, "8.98846567431158e+307");
Check((1n << 1024n) - (1n << 972n), "1.7976931348623155e+308");
Check((1n << 1024n) - (1n << 971n), "1.7976931348623157e+308");
Check((1n << 1024n) - (1n << 970n), "Infinity");  // Rounding up overflows.