In javascript, whether Bitwise OR use iee-754 as storage format during calculation nor not ？

Question

if Bitwise OR was used ieee-754 to calc the result in Javascript,i can't understand the result.

for example:

2|1 =>3

In ieee-754, 2 is stored as 0 10000000000 0000...0000,and 1 is stored as 0 01111111111 0000...0000

if exec bitwise or,i think the result is 0 11111111111 0000...0000,but why does it output 3?

As same as above,

example:

0.1|0 =>0

0 is stored as 0 00000000000 0000...0000,and 0.1 is stored as 0 01111111011 1001100110011001100110011001100110011001100110011010

if exec bitwise or,i think the result is 0 01111111011 1001100110011001100110011001100110011001100110011010,but why does it output 0,and lose decimal?

example:

2|-1 =>-1

2 is stored as 0 10000000000 0000...0000,and -1 is stored as 1 01111111111 0000...0000

if exec bitwise or,i think the result is 1 11111111111 0000...0000,but why does it output -1?

in javascript the number is converted to a 32 bit integer number, then the bitwise operation is made and the result is converted back to the standard format of 64 bit float.. — Nina Scholz, Apr 14 '19 at 08:03
here you go: [Bitwise Operators](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_Operators) — Nina Scholz, Apr 14 '19 at 08:09
[How do I convert a float number to a whole number in JavaScript?](//stackoverflow.com/a/12837315) Also [Read/Write bytes of float in JS](//stackoverflow.com/a/35748581) for actually type-punning so you could bitwise OR the bit-patterns of floating-point numbers. Not exactly a duplicate, though. — Peter Cordes, Apr 14 '19 at 08:09
Possible duplicate of [~ bitwise operator in JavaScript](https://stackoverflow.com/questions/32527807/bitwise-operator-in-javascript) (The answers there state that bitwise operators convert from `Number` (double) to 32 bit integer) — Peter Cordes, Apr 14 '19 at 08:15
but why 0.1|0 is output 0? As the document,number will convert to 32bit,but after bitwise or,the result should be `0 01111011 10011001100110011001101` — HanQ, Apr 14 '19 at 08:23
1.1|0 is output 1,also lose the decimal,i wonder that why the decimal was lost@NinaScholz.if javascript lose decimal in 32-bit,not use ieee-754 binary32 — HanQ, Apr 14 '19 at 08:30
@HanQ again, bitwise operations first convert the number to a 32 bit ***integer*** so `0.1` would be converted into `0b0` while `1.1` would be converted to `0b1` before the operation is even calculated. — VLAZ, Apr 14 '19 at 08:32
`0b` - prefix meaning "binary number" `0b0` - zero in binary, `0b10` is the binary number for the decimal `2`. — VLAZ, Apr 14 '19 at 08:50

Eric Postpischil · Answer 1 · 2019-04-14T10:44:47.400

JavaScript is an implementation of ECMAScript. The ECMAScript 2018 Language Specification (9th edition, June 2018) specifies the binary bitwise operators in clause 12.12. The evaluation steps in 12.12.3 include (using “@” to stand for one of the bitwise operations):

Let lnum be ? ToInt32(lval).
Let rnum be ? ToInt32(rval).
Return the result of applying the bitwise operator @ to lnum and rnum. The result is a signed 32-bit integer.

Thus, the bitwise operation is not performed on the bytes that represent a Number. The value of the Number is converted to a 32-bit two’s complement representation of an integer, and the operation is performed on those bits. Then resulting bits are then interpreted as a 32-bit two’s complement representation, so the value they represent becomes the value produced by the operation.

In javascript, whether Bitwise OR use iee-754 as storage format during calculation nor not ？

1 Answers1