libkern/ppc/bcmp.s

   1 /*
   2  * Copyright (c) 2000-2001 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * Copyright (c) 1999-2003 Apple Computer, Inc.  All Rights Reserved.
   7  *
   8  * This file contains Original Code and/or Modifications of Original Code
   9  * as defined in and that are subject to the Apple Public Source License
  10  * Version 2.0 (the 'License'). You may not use this file except in
  11  * compliance with the License. Please obtain a copy of the License at
  12  * http://www.opensource.apple.com/apsl/ and read it before using this
  13  * file.
  14  *
  15  * The Original Code and all software distributed under the License are
  16  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  17  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  18  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  19  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  20  * Please see the License for the specific language governing rights and
  21  * limitations under the License.
  22  *
  23  * @APPLE_LICENSE_HEADER_END@
  24  */
  25 ;
  26 #include <ppc/asm.h>
  27 #include <ppc/proc_reg.h>
  28 ;
  29 ; int   bcmp(const void *LHS, const void *RHS, size_t len);
  30 ;
  31 ; Because bcmp returns zero if equal and nonzero otherwise, it is slightly
  32 ; faster than memcmp, which returns the difference between the first different
  33 ; bytes.
  34 ;       r3 - LHS
  35 ;       r4 - RHS
  36 ;       r5 - len
  37
  38         .align  5
  39         .globl  EXT(bcmp)
  40 LEXT(bcmp)
  41
  42         cmpwi   cr1,r5,6                ; six chars long?
  43         mr      r6,r3                   ; copy LHS ptr so we can use r3 as result
  44         mr.     r3,r5                   ; test length and move to r3
  45         bgt     cr1,Llong               ; more than 6 chars long
  46         blt     cr1,Lshort              ; less than 6
  47
  48         ; most common operand length is 6 chars (enet addrs)
  49
  50         lwz     r8,0(r6)                ; first 4 bytes of LHS
  51         lwz     r7,0(r4)                ; and RHS
  52         lhz     r9,4(r6)                ; next 2 of LHS
  53         sub.    r3,r8,r7                ; compare first 4
  54         bnelr                           ; first 4 differed (r3!=0)
  55         lhz     r10,4(r4)               ; next 2 of RHS
  56         sub     r3,r9,r10               ; compare last 2
  57         blr                             ; done, result in r3
  58
  59         ; handle long strings
  60 Llong:
  61         srwi    r0,r5,2                 ; r0 = word len
  62         mtctr   r0                      ; set up for loop
  63 Llongloop:
  64         lwz     r8,0(r6)                ; next 4 bytes from LHS
  65         addi    r6,r6,4
  66         lwz     r7,0(r4)                ; next 4 from RHS
  67         addi    r4,r4,4
  68         sub.    r3,r8,r7                ; compare next 4 bytes
  69         bdnzt+  eq,Llongloop            ; loop if ctr!=0 and cr0_eq
  70         bnelr                           ; done if not equal (r3!=0)
  71
  72         andi.   r5,r5,3                 ; more to go?
  73
  74         ; compare short strings (0-5 bytes long)
  75         ;       r5 = length remaining
  76         ;       cr0= set on length
  77         ;       r3 = zero if length is zero
  78 Lshort:
  79         beqlr                           ; done (r3=0)
  80         mtctr   r5
  81 Lshortloop:
  82         lbz     r8,0(r6)                ; get next byte from LHS
  83         addi    r6,r6,1
  84         lbz     r7,0(r4)                ; and next byte from RHS
  85         addi    r4,r4,1
  86         sub.    r3,r8,r7                ; compare
  87         bdnzt+  eq,Lshortloop           ; loop if ctr!=0 and cr0_eq
  88         blr                             ; done, r3 set correctly by the subtract
  89