Thread: What does the syntax imply? EXAMPLE: if(VAL << x) & BIT15))

I do not understand what is happening in this statement.

Code:

#ifdef ENABLE_TEST_POINTS//tp_write_val(u16);
// Display a value using a test point
void tp_write_val(u16 val)
{
	u8 c;
	
	PC7_LOW;
	//PC7_HIGH;
	nop();
	nop();
	nop();
	PC7_LOW;
	for(c=0; c<15; c++)
	{
		if( (val << c) & BIT15 )
			PC7_HIGH;
		else
			PC7_LOW;
	}
	PC7_LOW;
	//PC7_HIGH;
	nop();
	nop();
	nop();
	//PC7_LOW;
}

What is ((val << c) & BIT15) about? I am sending 15 bits of data to this function and outputting the data serially onto a scope, testing someone else's code to ensue usability (RS-232 may not always be available). I do not understand how this code is comparing each bit as as the loop iterates. BIT15 is defined as 0x8000. PC7_HIGH simply makes test point 34 a high voltage, and PC7_LOW makes it low. I know I am missing something really simple...

please and thank you!

I'm a bit rusty on bitwise operators, and I don't know what data types "u8" and "u16" are, but the general function would be something like this:

"val" is a value passed to the function.
In the "for()" loop, "val" is shifted over by 'c' bits and logic-ANDed with BIT15.

If we assume "val" = 0x0800, then you can follow it like this:

Code:

(val << c) & BIT15

// c == 0
// shift val left 0 bit(s)
// val = 0x0800 = 0000 1000 0000 0000
// & BIT15:       1000 0000 0000 0000
//                -------------------
//                0000 0000 0000 0000
// "if()" is false, so output is PC7_LOW

(val << c) & BIT15

// c == 1
// shift val left 1 bit(s)
// val = 0x1000 = 0001 0000 0000 0000
// & BIT15:       1000 0000 0000 0000
//                -------------------
//                0000 0000 0000 0000
// "if()" is false, so output is PC7_LOW

(val << c) & BIT15

// c == 2
// shift val left 2 bit(s)
// val = 0x2000 = 0010 0000 0000 0000
// & BIT15:       1000 0000 0000 0000
//                -------------------
//                0000 0000 0000 0000
// "if()" is false, so output is PC7_LOW

(val << c) & BIT15

// c == 3
// shift val left 3 bit(s)
// val = 0x4000 = 0100 0000 0000 0000
// & BIT15:       1000 0000 0000 0000
//                -------------------
//                0000 0000 0000 0000
// "if()" is false, so output is PC7_LOW

(val << c) & BIT15

// c == 4
// shift val left 4 bit(s)
// val = 0x8000 = 1000 0000 0000 0000
// & BIT15:       1000 0000 0000 0000
//                -------------------
//                1000 0000 0000 0000
// "if()" is true, so output is PC7_HIGH

Thanks to all. Makes sense now. u16/u8 is unsigned type, for Raisonance products anyways.