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I would like to to use the bit addressable memory range (bdata) with an index variable as in the following example:
#define SETBIT(I) WAIT_4_MUTEX; flags^I=1; FREE_MUTEX; unsigned char bdata flags; func () { unsigned char i; for (i=0; i < MAX_CELL; i++) { // do interesting stuff SETBIT(i); } }
This construction of coarse gives a lval error on the use of the SETBIT macro.
My current fall back are the macro's:
#define SETBIT(I) base |= ((unsigned char) (1 << I)) #define CLEARBIT(I) base &= ~((unsigned char) (1 << I))
But still have the feeling that I am wasting cycles on the shift operators in these two macro's and because this is within a mutex region the timing might become an issue.
Is there a better way to set/reset the i-th bit of a bit addressable variable ?
The switch statement can be fast for some processors, that have efficient methods to call a jump table. But such processors normally also have a barrel shifter in which case they can shift n steps in constant time.
Easiest is if the caller can supply a constant value to or in, or the mask for clearing.
The switch statement can be fast for some processors, that have efficient methods to call a jump table.
JMP @A+DPTR ?
And if the compiler isn't clever enough to translate the switch/case structure this way, there is still the option of writing an assembly function.
This approach also works for more than 8 bits without any further effort, while the lookup table approach will need additional decision steps in such cases.