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/* Copyright (C) 1996 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by David Mosberger (davidm@cs.arizona.edu).

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

/* Finds characters in a memory area.  Optimized for the Alpha:

      - memory accessed as aligned quadwords only
      - uses cmpbge to compare 8 bytes in parallel
      - does binary search to find 0 byte in last
        quadword (HAKMEM needed 12 instructions to
        do this instead of the 9 instructions that
        binary search needs).

For correctness consider that:

      - only minimum number of quadwords may be accessed
      - the third argument is an unsigned long
*/

        .set noreorder
        .set noat

        .globl memchr
        .ent memchr
memchr:
        .frame $30,0,$26,0
        .prologue 0

        # Hack -- if someone passes in (size_t)-1, hoping to just
        # search til the end of the address space, we will overflow
        # below when we find the address of the last byte.  Given
        # that we will never have a 56-bit address space, cropping
        # the length is the easiest way to avoid trouble.
        zap     $18, 0x80, $5   #-e0    :

        beq     $18, $not_found # .. e1 :
        ldq_u   $1, 0($16)      # e1    : load first quadword
        insbl   $17, 1, $2      # .. e0 : $2 = 000000000000ch00
        and     $17, 0xff, $17  #-e0    : $17 = 00000000000000ch
        cmpult  $18, 9, $4      # .. e1 :
        or      $2, $17, $17    # e0    : $17 = 000000000000chch
        lda     $3, -1($31)     # .. e1 :
        sll     $17, 16, $2     #-e0    : $2 = 00000000chch0000
        addq    $16, $5, $5     # .. e1 :
        or      $2, $17, $17    # e1    : $17 = 00000000chchchch
        unop                    #       :
        sll     $17, 32, $2     #-e0    : $2 = chchchch00000000
        or      $2, $17, $17    # e1    : $17 = chchchchchchchch
        extql   $1, $16, $7     # e0    : 
        beq     $4, $first_quad # .. e1 :

        ldq_u   $6, -1($5)      #-e1    : eight or less bytes to search
        extqh   $6, $16, $6     # .. e0 :
        mov     $16, $0         # e0    :
        or      $7, $6, $1      # .. e1 : $1 = quadword starting at $16

        # Deal with the case where at most 8 bytes remain to be searched
        # in $1.  E.g.:
        #       $18 = 6
        #       $1 = ????c6c5c4c3c2c1
$last_quad:
        negq    $18, $6         #-e0    :
        xor     $17, $1, $1     # .. e1 :
        srl     $3, $6, $6      # e0    : $6 = mask of $18 bits set
        cmpbge  $31, $1, $2     # .. e1 :
        and     $2, $6, $2      #-e0    :
        beq     $2, $not_found  # .. e1 :

$found_it:
        # Now, determine which byte matched:
        negq    $2, $3          # e0    :
        and     $2, $3, $2      # e1    :

        and     $2, 0x0f, $1    #-e0    :
        addq    $0, 4, $3       # .. e1 :
        cmoveq  $1, $3, $0      # e0    :

        addq    $0, 2, $3       # .. e1 :
        and     $2, 0x33, $1    #-e0    :
        cmoveq  $1, $3, $0      # .. e1 :

        and     $2, 0x55, $1    # e0    :
        addq    $0, 1, $3       # .. e1 :
        cmoveq  $1, $3, $0      #-e0    :

$done:  ret                     # .. e1 :

        # Deal with the case where $18 > 8 bytes remain to be
        # searched.  $16 may not be aligned.
        .align 4
$first_quad:
        andnot  $16, 0x7, $0    #-e1    :
        insqh   $3, $16, $2     # .. e0 : $2 = 0000ffffffffffff ($16<0:2> ff)
        xor     $1, $17, $1     # e0    :
        or      $1, $2, $1      # e1    : $1 = ====ffffffffffff
        cmpbge  $31, $1, $2     #-e0    :
        bne     $2, $found_it   # .. e1 :

        # At least one byte left to process.

        ldq     $1, 8($0)       # e0    :
        subq    $5, 1, $18      # .. e1 :
        addq    $0, 8, $0       #-e0    :

        # Make $18 point to last quad to be accessed (the
        # last quad may or may not be partial).

        andnot  $18, 0x7, $18   # .. e1 :
        cmpult  $0, $18, $2     # e0    :
        beq     $2, $final      # .. e1 :

        # At least two quads remain to be accessed.

        subq    $18, $0, $4     #-e0    : $4 <- nr quads to be processed
        and     $4, 8, $4       # e1    : odd number of quads?
        bne     $4, $odd_quad_count # e1 :

        # At least three quads remain to be accessed

        mov     $1, $4          # e0    : move prefetched value to correct reg

        .align  4
$unrolled_loop:
        ldq     $1, 8($0)       #-e0    : prefetch $1
        xor     $17, $4, $2     # .. e1 :
        cmpbge  $31, $2, $2     # e0    :
        bne     $2, $found_it   # .. e1 :

        addq    $0, 8, $0       #-e0    :
$odd_quad_count:
        xor     $17, $1, $2     # .. e1 :
        ldq     $4, 8($0)       # e0    : prefetch $4
        cmpbge  $31, $2, $2     # .. e1 :
        addq    $0, 8, $6       #-e0    :
        bne     $2, $found_it   # .. e1 :

        cmpult  $6, $18, $6     # e0    :
        addq    $0, 8, $0       # .. e1 :
        bne     $6, $unrolled_loop #-e1 :

        mov     $4, $1          # e0    : move prefetched value into $1
$final: subq    $5, $0, $18     # .. e1 : $18 <- number of bytes left to do
        bne     $18, $last_quad # e1    :

$not_found:
        mov     $31, $0         #-e0    :
        ret                     # .. e1 :

        .end memchr