bit shifts of constants

[stevech]

does ZB have a compile-time operator, for constants, for left/right shift?

like
(1<<constant1) OR (1<<constant2)

versus
shl(1, constant1) OR shl(1, constant2)

shl() is run-time, I suppose, unless the compiler's optimizer converts the above to a compile-time constant rather than using run time function calls despite the constants

[dkinzer]

does ZB have a compile-time operator, for constants, for left/right shift?

For many functions, including Shl and Shr, if the parameters are constant the compiler computes the result at compile-time. This can be seen, for example, by compiling this code:

Code: Select all

Dim b as Byte
Sub Main()
    b = Shl(1, 5)
End Sub

which results in this intermediate C code (for native mode devices):

Code: Select all

static uint8_t mzv_b;
void zf_Main(void)
{
	mzv_b = 32;
}

or this VM code:

Code: Select all

            Sub Main()
            	b = Shl(1, 5)
0019 1a20        PSHI_B         0x20 (32)
001b 204001      POPA_B         0x0140 (320)
            End Sub
001e 06          RET

[dkinzer]

I should have remarked that the same compile-time computation applies to expressions with constant operands, too, so your example of shl(1, constant1) OR shl(1, constant2) will evaluate to a constant at compile-time.

[stevech]

Thanks. I assume that applies as well where the storage is an I/O register

DDRB
or SPI register, etc.

[dkinzer]

I assume that applies as well where the storage is an I/O register.

Yes. The use to which an expression's value is put is immaterial - the compiler will optimize an expression as much as it can, possibly reducing it to a constant value.