avr-gcc: Addition/Subtraktion mit Saturierung

#include <stdfix.h>

#include <stdint.h>

static inline __attribute__((always_inline))

uint16_t add_satu16 (uint16_t a, uint16_t b)

{

    unsigned sat fract fa = urbits (a);

    unsigned sat fract fb = urbits (b);

    return bitsur (fa + fb);

}

uint16_t add1 (uint16_t a)

{

    return add_satu16 (a, 1);

}

uint16_t addm1 (uint16_t a)

{

    return add_satu16 (a, -1u);

}

uint16_t add2 (uint16_t a, uint16_t b)

{

    return add_satu16 (a, b);

}

add1:

  adiw r24,1

  brcc 0f

  sbc r25,r25

  mov r24,r25

  0:

  ret

addm1:

  sbiw r24,1

  brcs 0f

  ldi r25,0xff

  mov r24,r25

  0:

  ret

add2:

  add r24,r22

  adc r25,r23

  brcc 0f

  sbc r25,r25

  mov r24,r25

  0:

  ret