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Annotation of sys/lib/libkern/arch/alpha/byte_swap_4.S, Revision 1.1.1.1

1.1       nbrk        1: /*     $OpenBSD: byte_swap_4.S,v 1.2 1996/10/31 00:43:15 niklas Exp $  */
                      2: /*     $NetBSD: byte_swap_4.S,v 1.2 1996/10/17 04:26:22 cgd Exp $      */
                      3:
                      4: /*
                      5:  * Copyright (c) 1996 Carnegie-Mellon University.
                      6:  * All rights reserved.
                      7:  *
                      8:  * Author: Chris G. Demetriou
                      9:  *
                     10:  * Permission to use, copy, modify and distribute this software and
                     11:  * its documentation is hereby granted, provided that both the copyright
                     12:  * notice and this permission notice appear in all copies of the
                     13:  * software, derivative works or modified versions, and any portions
                     14:  * thereof, and that both notices appear in supporting documentation.
                     15:  *
                     16:  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
                     17:  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
                     18:  * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
                     19:  *
                     20:  * Carnegie Mellon requests users of this software to return to
                     21:  *
                     22:  *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
                     23:  *  School of Computer Science
                     24:  *  Carnegie Mellon University
                     25:  *  Pittsburgh PA 15213-3890
                     26:  *
                     27:  * any improvements or extensions that they make and grant Carnegie the
                     28:  * rights to redistribute these changes.
                     29:  */
                     30:
                     31: #include <machine/asm.h>
                     32:
                     33: #ifndef NAME
                     34: #define        NAME byte_swap_4
                     35: #endif
                     36:
                     37: /*
                     38:  * Byte-swap a 4-byte quantity.  (Convert 0x01234567 to 0x67452301.)
                     39:  *
                     40:  * Argument is an unsigned 4-byte integer (u_int32_t).
                     41:  */
                     42: LEAF(NAME, 1)                  /* a0 contains 0x01234567 */
                     43:        extbl   a0, 0, t0       /* t0 = 0x      67 */
                     44:        extbl   a0, 1, t1       /* t1 = 0x      45 */
                     45:        extbl   a0, 2, t2       /* t2 = 0x      23 */
                     46:        extbl   a0, 3, t3       /* t3 = 0x      01 */
                     47:        sll     t0, 24, t0      /* t0 = 0x67       */
                     48:        sll     t1, 16, t1      /* t1 = 0x  45     */
                     49:        sll     t2, 8, t2       /* t2 = 0x    23   */
                     50:        or      t3, t0, v0      /* v0 = 0x67    01 */
                     51:        or      t1, t2, t1      /* t1 = 0x  4523   */
                     52:        or      t1, v0, v0      /* v0 = 0x67452301 */
                     53:        RET
                     54: END(NAME)