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Annotation of kernel/machdep/i386/libc/memcmp.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
        !             3:  *
        !             4:  * @APPLE_LICENSE_HEADER_START@
        !             5:  * 
        !             6:  * Portions Copyright (c) 1999 Apple Computer, Inc.  All Rights
        !             7:  * Reserved.  This file contains Original Code and/or Modifications of
        !             8:  * Original Code as defined in and that are subject to the Apple Public
        !             9:  * Source License Version 1.1 (the "License").  You may not use this file
        !            10:  * except in compliance with the License.  Please obtain a copy of the
        !            11:  * License at http://www.apple.com/publicsource and read it before using
        !            12:  * this file.
        !            13:  * 
        !            14:  * The Original Code and all software distributed under the License are
        !            15:  * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
        !            16:  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
        !            17:  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
        !            18:  * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
        !            19:  * License for the specific language governing rights and limitations
        !            20:  * under the License.
        !            21:  * 
        !            22:  * @APPLE_LICENSE_HEADER_END@
        !            23:  */
        !            24: 
        !            25: /* Copyright (c) 1991 NeXT Computer, Inc.  All rights reserved.
        !            26:  *
        !            27:  *      File:   libc/i386/ansi/memcmp.c
        !            28:  *      Author: Bruce Martin, NeXT Computer, Inc.
        !            29:  *
        !            30:  *      This file contains machine dependent code for block compares
        !            31:  *      on NeXT i386-based products.  Currently tuned for the i486.
        !            32:  *
        !            33:  * HISTORY
        !            34:  * 12-Aug-92  Bruce Martin ([email protected])
        !            35:  *     Created.
        !            36:  */
        !            37: 
        !            38: /*
        !            39:  * 486 factoids:
        !            40:  *     - Using 'repe cmp' is a very marginal win.  You can easily beat it
        !            41:  *     with a aggressively unrolled loop, but that typically has much more
        !            42:  *     setup time.  So, we go with less setup, assuming shorter comparisons
        !            43:  *     will be the rule.
        !            44:  */
        !            45: 
        !            46: 
        !            47: #define MIN_TO_ALIGN   16
        !            48: 
        !            49: /*
        !            50:  * Convert a void * into a unsigned int so arithmetic can be done
        !            51:  * (Technically, the gnu C compiler is tolerant of arithmetic
        !            52:  * on void *, but ansi isn't; so we do this.)
        !            53:  */
        !            54: #define UNS(voidp)      ((unsigned int)(voidp))
        !            55: 
        !            56: /*
        !            57:  * Number of bytes addr is past an integer alignment
        !            58:  */
        !            59: #define BYTES_PAST_INT_ALIGNMENT(voidp)        (UNS(voidp) & (sizeof(int) - 1))
        !            60: 
        !            61: #if defined(NX_CURRENT_COMPILER_RELEASE) && (NX_CURRENT_COMPILER_RELEASE < 320)
        !            62: #define SIREG "e"
        !            63: #else
        !            64: #define SIREG "S"
        !            65: #endif
        !            66: 
        !            67: 
        !            68: static inline char
        !            69: simple_fwd_char_cmp(const char *s1, const char *s2, int len)
        !            70: {
        !            71:     int diff;
        !            72:     asm("      repe; cmpsb
        !            73:                jz 1f
        !            74:                movb -1(%2), %1
        !            75:                movb -1(%3), %2
        !            76:                subb %2, %1
        !            77:        1:      movl %1, %0
        !            78:        "
        !            79:        : "=r" (diff)
        !            80:        : "c" (len), "D" (s1), SIREG (s2)
        !            81:        : "ecx", "edi", "esi");
        !            82:     return diff;
        !            83: }
        !            84: 
        !            85: static inline int
        !            86: simple_fwd_int_cmp(const int *s1, const int *s2, int len)
        !            87: {
        !            88:     int diff;
        !            89:     len >>= 2;
        !            90:     asm("      repe; cmpsl
        !            91:                jz 1f
        !            92:                movl -4(%2), %1
        !            93:                movl -4(%3), %2
        !            94:                subl %2, %1
        !            95:        1:      movl %1, %0
        !            96:        "
        !            97:        : "=r" (diff)
        !            98:        : "c" (len), "D" (s1), SIREG (s2)
        !            99:        : "ecx", "edi", "esi");
        !           100:     return diff;
        !           101: }
        !           102: 
        !           103: 
        !           104: int memcmp(const void *, const void *, unsigned long);
        !           105: 
        !           106: int bcmp(const void *src1, const void *src2, unsigned long ulen)
        !           107: {
        !           108:     return memcmp(src1, src2, ulen);
        !           109: }
        !           110: 
        !           111: 
        !           112: int memcmp(const void *s1, const void *s2, unsigned long ulen)
        !           113: {
        !           114:     int len = ulen;
        !           115:     int need_to_cmp;
        !           116:     int res;
        !           117:     
        !           118:     if (len == 0)
        !           119:        return 0;
        !           120: 
        !           121:     /* Always do a forward compare */
        !           122: 
        !           123:     if (len < MIN_TO_ALIGN) {
        !           124:        return simple_fwd_char_cmp(s1, s2, len);
        !           125:     }
        !           126: 
        !           127:     if (need_to_cmp = BYTES_PAST_INT_ALIGNMENT(s2)) {
        !           128:        need_to_cmp = sizeof(int) - need_to_cmp;
        !           129:        if (res = simple_fwd_char_cmp(s1, s2, need_to_cmp))
        !           130:            return res;
        !           131:        len -= need_to_cmp;
        !           132:        UNS(s1) += need_to_cmp;
        !           133:        UNS(s2) += need_to_cmp;
        !           134:     }
        !           135: 
        !           136:     res = simple_fwd_int_cmp(s1, s2, len);
        !           137:        
        !           138:     if (!res && (need_to_cmp = (len & 3))) {
        !           139:        UNS(s2) += (len & ~3);
        !           140:        UNS(s1) += (len & ~3);
        !           141:        res = simple_fwd_char_cmp(s1, s2, need_to_cmp);
        !           142:     }
        !           143:     return res;
        !           144: }

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