Re: [avr-gcc-list] gcc binary

[Dave Hansen]

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From: Joerg Wunsch <address@hidden>
[...]
> As "E. Weddington" <address@hidden> wrote:
>
> >Worse: its not even a part of the C language. It has nothing to do
> >with GCC, or the AVR.
>
> It seems to be quite common among µC C compilers.  Unlike the PORTB.0
> notation where I don't see how this would ever fit at all into legal C
> syntax, I can imagine that 0b is a perferctly legal vendor extension
> for a compiler.

I believe it was proposed for the C99 standard, but nobody pushed it 
through.

> Just curious, I've once made a patch for GCC that implements it.  This
> was merely intented to be a proof of concept.  Does anyone
> incidentally know whether this feature might have already been
> proposed (and perhaps put down) to the GCC folks?  If not, do people
> feel I should submit that patch?
>
> In case anyone is interested:
>
> http://www.sax.de/~joerg/gcc-0b.patch

Tom Torfs posted the following preprocessor hack in comp.arch.embedded.  I 
haven't tried it yet, but it should work on a standard compiler.

Regards,

  -=Dave

/* Binary constant generator macro
  By Tom Torfs - donated to the public domain
*/

/* All macro's evaluate to compile-time constants */

/* *** helper macros *** /

/* turn a numeric literal into a hex constant
  (avoids problems with leading zeroes)
  8-bit constants max value 0x11111111, always fits in unsigned long
*/
#define HEX__(n) 0x##n##LU

/* 8-bit conversion function */
#define B8__(x) ((x&0x0000000FLU)?1:0)      \
              +((x&0x000000F0LU)?2:0)       \
              +((x&0x00000F00LU)?4:0)       \
              +((x&0x0000F000LU)?8:0)       \
              +((x&0x000F0000LU)?16:0)      \
              +((x&0x00F00000LU)?32:0)      \
              +((x&0x0F000000LU)?64:0)      \
              +((x&0xF0000000LU)?128:0)

/* *** user macros *** /

/* for upto 8-bit binary constants */
#define B8(d) ((unsigned char)B8__(HEX__(d)))

/* for upto 16-bit binary constants, MSB first */
#define B16(dmsb,dlsb) (((unsigned short)B8(dmsb)<<8)     \
                        + B8(dlsb))

/* for upto 32-bit binary constants, MSB first */
#define B32(dmsb,db2,db3,dlsb) (((unsigned long)B8(dmsb)<<24)      \
                                  + ((unsigned long)B8(db2)<<16) \
                                  + ((unsigned long)B8(db3)<<8)    \
                                  + B8(dlsb))

/* Sample usage:
     B8(01010101) = 85
     B16(10101010,01010101) = 43605
     B32(10000000,11111111,10101010,01010101) = 2164238933
*/

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