/*      $NetBSD: strlen.S,v 1.1 2005/12/20 19:28:50 christos Exp $      */

/*
 * Copyright 2002 Wasabi Systems, Inc.
 * All rights reserved.
 *
 * Written by Eduardo Horvath for Wasabi Systems, Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed for the NetBSD Project by
 *      Wasabi Systems, Inc.
 * 4. The name of Wasabi Systems, Inc. may not be used to endorse
 *    or promote products derived from this software without specific prior
 *    written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY WASABI SYSTEMS, INC. ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL WASABI SYSTEMS, INC
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */



#include <machine/asm.h>
#if defined(LIBC_SCCS) && !defined(lint)
        RCSID("$NetBSD: strlen.S,v 1.1 2005/12/20 19:28:50 christos Exp $")
#endif /* LIBC_SCCS and not lint */
        
/* The algorithm here uses the following techniques:
 *
 * 1) Given a word 'x', we can test to see if it contains any 0 bytes
 *    by subtracting 0x01010101, and seeing if any of the high bits of each
 *    byte changed from 0 to 1. This works because the least significant
 *    0 byte must have had no incoming carry (otherwise it's not the least
 *    significant), so it is 0x00 - 0x01 == 0xff. For all other
 *    byte values, either they have the high bit set initially, or when
 *    1 is subtracted you get a value in the range 0x00-0x7f, none of which
 *    have their high bit set. The expression here is
 *    (x + 0xfefefeff) & ~(x | 0x7f7f7f7f), which gives 0x00000000 when
 *    there were no 0x00 bytes in the word.
 *
 * 2) Now just hunt for the first byte that's 0x00 in 'x'.
 *
 *    This is from the book 'The PowerPC Compiler Writer's Guide',
 *    by Steve Hoxey, Faraydon Karim, Bill Hay and Hank Warren.
 */

ENTRY(strlen)
        /*
         * Calculate address for and load the first xword.
         */
        andn    %o0, 0x7, %o1
        ldx     [%o1], %g1

        /*
         * Now prepare some constants while the data arrives...
         */
        sethi   %hi(0xfefefefe), %o3
        sethi   %hi(0x7f7f7f7f), %o2
        
        or      %o3, %lo(0xfefefefe), %o3
        or      %o2, %lo(0x7f7f7f7f), %o2
        
        sllx    %o3, 32, %o5
        andcc   %o0, 0x7, %g5   ! Hoisted from below to fill a slot
        
        sllx    %o2, 32, %o4
        or      %o3, %o5, %o3
        
        sll     %g5, 3, %g5     ! Convert to bytes. hoisted
        or      %o2, %o4, %o2
        
        inc     %o3
        neg     %g5             ! hoisted

        /*
         * Mask off the leading bits:
         *
         * if (ptr & 0x7)
         *      mask = -1 << (64 - ((ptr & 0x7) << 3));
         */
        
!       andcc   %o0, 0x7, %g5   ! Hoisted above
        bz,pt   %icc, 0f
        
        
!        sll    %g5, 3, %g5     ! Convert to bytes. Also hoisted

!       neg     %g5             ! Hoisted
        
         add    %g5, 64, %g5
        mov     -1, %o4
        
        sllx    %o4, %g5, %o4

        or      %o4, %g1, %g1   ! Make leading bytes != 0
        
0:
        or      %g1, %o2, %o5   ! Do step 1 -- use or/andn instead of nor/and
        add     %g1, %o3, %g5
        
        inc     8, %o1          ! Point to next word
        andncc  %g5, %o5, %g0
        bz,a,pt %xcc, 0b
         ldx    [%o1], %g1
        
        mov     -1, %o4
        dec     8, %o1
        
        sllx    %o4, 64-8, %o5
        
        btst    %g1, %o5        ! Check high byte
        bz      %xcc,0f
         srlx   %o5, 8, %o5

        inc     %o1
        btst    %g1, %o5        ! Check 2nd byte
        bz      %xcc,0f
         srlx   %o5, 8, %o5
        
        inc     %o1
        btst    %g1, %o5        ! Check 3rd byte
        bz      %xcc,0f
         srlx   %o5, 8, %o5

        inc     %o1
        btst    %g1, %o5        ! Check 4th byte
        bz      %xcc,0f
         srlx   %o5, 8, %o5
                        
        inc     %o1
        btst    %g1, %o5        ! Check 5th byte
        bz      %xcc,0f
         srlx   %o5, 8, %o5
                        
        inc     %o1
        btst    %g1, %o5        ! Check 6th byte
        bz      %xcc,0f
         srlx   %o5, 8, %o5
                        
        inc     %o1
        btst    %g1, %o5        ! Check 7th byte
        bz      %xcc,0f
         nop

        inc     %o1
0:
        retl
         sub    %o1, %o0, %o0   ! return length (ptr - (origptr+1))