Why write 1,000,000,000 as 1000*1000*1000 in C?
In code created by Apple, there is this line:
CMTimeMakeWithSeconds( newDurationSeconds, 1000*1000*1000 )
Is there any reason to express 1,000,000,000 as 1000*1000*1000 ?
Why not 1000^3 for that matter?
One reason to declare constants in a multiplicative way is to improve readability, while the run-time performance is not affected. Also, to indicate that the writer was thinking in a multiplicative manner about the number.
Consider this:
double memoryBytes = 1024 * 1024 * 1024;
It's clearly better than:
double memoryBytes = 1073741824;
as the latter doesn't look, at first glance, the third power of 1024.
As Amin Negm-Awad mentioned, the ^ operator is the binary XOR . Many languages lack the built-in, compile-time exponentiation operator, hence the multiplication.
Why not 1000^3 ?
The result of 1000^3 is 1003. ^ is the bit-XOR operator.
Even it does not deal with the Q itself, I add a clarification. x^y does not always evaluate to x+y as it does in the questioner's example. You have to xor every bit. In the case of the example:
1111101000₂ (1000₁₀)
0000000011₂ (3₁₀)
1111101011₂ (1003₁₀)
But
1111101001₂ (1001₁₀)
0000000011₂ (3₁₀)
1111101010₂ (1002₁₀)
There are reasons not to use 1000 * 1000 * 1000 .
With 16-bit int , 1000 * 1000 overflows. So using 1000 * 1000 * 1000 reduces portability.
With 32-bit int , the following overflows.
long long Duration = 1000 * 1000 * 1000 * 1000; // overflow
long long Duration = 1000000000000; // no overflow, hard to read
Suggest that the lead value matches the type of the destination for readability, portability and correctness.
double Duration = 1000.0 * 1000 * 1000;
long long Duration = 1000LL * 1000 * 1000 * 1000;
Also could simple use e notation for values that are exactly representable as a double . Of course this leads to knowing if double can exactly represent the whole number value - something of concern with values greater than 1e9. (See DBL_EPSILON and DBL_DIG ).
long Duration = 1000000000;
// vs.
long Duration = 1e9;
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