I am trying to implement Dmitry's bit reversal algorithm under HiTech =
PICC, but am having a problem with the variables.

The function I have is:

char reverse_bits(char source)// reverses bits 0 to 6 - source =3D =
0ABCDEFG
{
char result;=20
#asm
        swapf   _source,w       ;W=3D DEFG0ABC
        btfsc   _source,3        ; If D =3D 1,
        xorlw  0x88                ;convert now sure W=3D 0EFGDABC

        btfsc   _source,6        ;Test bit A
         xorlw  0x05               ;Invert bits A and C
        btfsc   _source,4        ;Test bit C
         xorlw  0x05             ;Invert bits A and C
                                       ;now W =3D 0EFGDCBA
        btfsc   _source,2        ;Do the same with E and G
         xorlw  0x50
        btfsc   _source,0
         xorlw  0x50
        movwf _result          ;so now W =3D 0GFEDCBA (done)
#endasm
return(result);
}

But, on building, the linker says that _source and _result are undefined =
variables. I thought that, to use a C variable in a piece of assembler =
code, you simply prepend an underscore to it. Anyone know what I'm doing =
wrong?

Graham

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