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From: "wvangulik at xs4all dot nl" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/29524] [4.2/4.3 Regression] Too much RAM used: __clz_tab[] linked
Date: Wed, 24 Oct 2007 11:16:00 -0000	[thread overview]
Message-ID: <20071024111648.17609.qmail@sourceware.org> (raw)
In-Reply-To: <bug-29524-10671@http.gcc.gnu.org/bugzilla/>



------- Comment #13 from wvangulik at xs4all dot nl  2007-10-24 11:16 -------
(In reply to comment #10)

Something like this is smaller, faster and works for all registers (no need for
LD_regs). And could easily be writtin in to a insn:

; rOut: output register
; rIn:  input register
; rIn, Z, N are clobbered, C is set
clzqi_init:
    clr rOut           ; clear to zero
    neg rOut           ; make -1, and set C (C used for garanteed termination)
clzqi_loop1:
    inc rOut           ; inc output (C not touched)
    rol rIn            ; push MSB into C
    brcc clz_loop1     ; if C is cleared (msb was not set), continue loop
clzqi_end:

A clz on a hi/si/di would be almost the same. Extend the "rol rIn" to a rol per
sub_reg.
Of course there can be speed optimisation for hi/si/di, but for the AVR the
optimizer is in most cases set for size.
A library call to this is shorter but it may impose extra mov instruction to
fit the register constraints.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29524


  parent reply	other threads:[~2007-10-24 11:16 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2006-10-20 12:26 [Bug c/29524] New: " batt at develer dot com
2006-10-20 14:40 ` [Bug middle-end/29524] " rguenth at gcc dot gnu dot org
2006-10-20 15:59 ` [Bug other/29524] " pinskia at gcc dot gnu dot org
2006-10-20 16:19 ` pinskia at gcc dot gnu dot org
2006-10-23 19:09 ` batt at develer dot com
2006-11-07 11:10 ` batt at develer dot com
2006-12-03 21:41 ` [Bug target/29524] [4.2/4.3 Regression] " pinskia at gcc dot gnu dot org
2007-02-19 20:33 ` mmitchel at gcc dot gnu dot org
2007-04-02 21:47 ` giovannibajo at libero dot it
2007-05-14 21:32 ` mmitchel at gcc dot gnu dot org
2007-07-23 22:57 ` eweddington at cso dot atmel dot com
2007-07-23 22:58 ` eweddington at cso dot atmel dot com
2007-09-08 21:44 ` anrp at mit dot edu
2007-09-08 21:48 ` anrp at mit dot edu
2007-10-09 19:30 ` mmitchel at gcc dot gnu dot org
2007-10-24 11:16 ` wvangulik at xs4all dot nl [this message]
2007-11-30 14:59 ` wvangulik at xs4all dot nl
2007-12-22 17:15 ` j at uriah dot heep dot sax dot de
2007-12-23 20:15 ` wvangulik at xs4all dot nl
2008-01-18 18:16 ` pmarques at grupopie dot com
2008-02-01 16:58 ` jsm28 at gcc dot gnu dot org
2008-05-19 20:47 ` [Bug target/29524] [4.2/4.3/4.4 " jsm28 at gcc dot gnu dot org
2009-03-31 19:48 ` [Bug target/29524] [4.3/4.4/4.5 " jsm28 at gcc dot gnu dot org
2009-08-04 12:39 ` rguenth at gcc dot gnu dot org
2010-05-22 18:23 ` [Bug target/29524] [4.3/4.4/4.5/4.6 " rguenth at gcc dot gnu dot org

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