Bitwise operators are very fast in AS3, so here is a small collection of code snippets which can speed up certain computations. I won’t explain what bit operators are and how to use them, rather pointing to an excellent article hosted on gamedev.net: ‘Bitwise Operations in C’.
If you know any good tricks that are not included here, feel free to leave a comment or send me an email. All benchmarks were done in AS3.
Left bit shifting to multiply by any power of two
Approximately 300% faster.
x = x * 2; x = x * 64; //equals: x = x << 1; x = x << 6;
Right bit shifting to divide by any power of two
Approximately 350% faster.
x = x / 2; x = x / 64; //equals: x = x >> 1; x = x >> 6;
Number to integer conversion
Using int(x) is 10% faster in AS3. Still the bitwise version works better in AS2.
x = int(1.232) //equals: x = 1.232 >> 0;
Extracting color components
Not really a trick, but the regular way of extracting values using bit masking and shifting.
//24bit var color:uint = 0x336699; var r:uint = color >> 16; var g:uint = color >> 8 & 0xFF; var b:uint = color & 0xFF; //32bit var color:uint = 0xff336699; var a:uint = color >>> 24; var r:uint = color >>> 16 & 0xFF; var g:uint = color >>> 8 & 0xFF; var b:uint = color & 0xFF;
Combining color components
‘Shift up’ the values into the correct position and combine them.
//24bit var r:uint = 0x33; var g:uint = 0x66; var b:uint = 0x99; var color:uint = r << 16 | g << 8 | b; //32bit var a:uint = 0xff; var r:uint = 0x33; var g:uint = 0x66; var b:uint = 0x99; var color:uint = a << 24 | r << 16 | g << 8 | b;
Swap integers without a temporary variable using XOR
Pretty neat trick, it is explained in detail in the link at the top of the page. This is 20% faster.
var t:int = a; a = b; b = t; //equals: a ^= b; b ^= a; a ^= b;
This is much slower than the pre/post decrement operator, but a nice way to obfuscate your code ;-)
i = -~i; // i++ i = ~-i; // i--
Sign flipping using NOT or XOR
Strangely enough, this is 300%(!) faster.
i = -i; //equals i = ~i + 1; //or i = (i ^ -1) + 1;
Fast modulo operation using bitwise AND
If the divisor is a power of 2, the modulo (%) operation can be done with:
modulus = numerator & (divisor – 1);
This is about 600% faster.
x = 131 % 4; //equals: x = 131 & (4 - 1);
Check if an integer is even/uneven using bitwise AND
This is 600% faster.
isEven = (i % 2) == 0; //equals: isEven = (i & 1) == 0;
Forget Math.abs() for time critical code. Version 1 is 2500% faster than Math.abs(), and the funky bitwise version 2 is again 20% faster than version 1.
//version 1 i = x < 0 ? -x : x; //version 2 i = (x ^ (x >> 31)) - (x >> 31);
Comparing two integers for equal sign
This is 35% faster.
eqSign = a * b > 0; //equals: eqSign = a ^ b >= 0;
Fast color conversion from R5G5B5 to R8G8B8 pixel format using shifts
R8 = (R5 << 3) | (R5 >> 2) G8 = (R5 << 3) | (R5 >> 2) B8 = (R5 << 3) | (R5 >> 2)