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# ECMAScript outputs

Figure 2-5
Negative numbers are also stored in binary code, but in a format called
two’s complement
. The two’s com-
plement of a number is calculated in three steps:
1.
Determine the binary representation of the non-negative version (for example, to find –18, first
determine the binary representation of 18).
2.
Find the one’s complement of the number, which essentially means that every 0 must be
replaced with 1 and vice versa.
3.
Add 1 to the one’s complement.
To determine the binary representation for –18, you must first take the binary representation of 18,
which is:
0000 0000 0000 0000 0000 0000 0001 0010
Next, take the one’s complement, which is the inverse:
1111 1111 1111 1111 1111 1111 1110 1101
Finally, add 1 to the one’s complement:
1111 1111 1111 1111 1111 1111 1110 1101
1
---------------------------------------
1111 1111 1111 1111 1111 1111 1110 1110
So, the binary equivalent of –18 is 1111 1111 1111 1111 1111 1111 1110 1110. Keep in mind that the devel-
oper has no access to bit 31 when dealing with signed integers.
The interesting thing about negative integers is that conversion to a binary string does not show the
two’s complement form. Instead, ECMAScript outputs the standard binary code for the number ’s abso-
lute value preceded by a minus sign. For example:
var iNum = -18;
This code outputs only
“-10010”
instead of the two’s complement in order to protect bit 31 from being
accessed. To put it simply, ECMAScript aims to deal with integers in such a simple way that developers
need not spend any time worrying about their usage.
10010
(2
4
x1) + (2
3
x0) + (2
2
x0) + (2
1
x1) + (2
0
x0)
16 + 0 0
0
2
+++
18
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Chapter 2
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