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Re: [avr-gcc-list] Is it possible to implement...

From: Joerg Wunsch
Subject: Re: [avr-gcc-list] Is it possible to implement...
Date: Mon, 6 Jan 2003 10:15:43 +0100 (MET)

address@hidden wrote:

> I am not (yet) a user of avr-gcc but I would assume the compiler is
> internally optimized for 16/8 bit adds and thus would already
> implement 16 bits adds optimized as you describe.

Yes, it does:

$ /usr/local/lib/gcc-lib/avr/3.3/cc1 -quiet -O -o -
int foo(int c) { extern int i; i += c;  return i; }
        .file   "<stdin>"
        .arch avr2
__SREG__ = 0x3f
__SP_H__ = 0x3e
__SP_L__ = 0x3d
__tmp_reg__ = 0
__zero_reg__ = 1
        .global __do_copy_data
        .global __do_clear_bss
.global foo
        .type   foo, @function
/* prologue: frame size=0 */
/* prologue end (size=0) */
        lds r18,i
        lds r19,(i)+1
        add r24,r18
        adc r25,r19
        sts (i)+1,r25
        sts i,r24
/* epilogue: frame size=0 */
/* epilogue end (size=1) */
/* function foo size 11 (10) */
        .size   foo, .-foo
/* File "<stdin>": code   11 = 0x000b (  10), prologues   0, epilogues   1 */

Well, if the increment is constant, it can use "adiw" instead.
J"org Wunsch                                           Unix support engineer
address@hidden        http://www.interface-systems.de/~j/
avr-gcc-list at http://avr1.org

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