github.com/tidwall/go@v0.0.0-20170415222209-6694a6888b7d/src/runtime/memmove_plan9_386.s (about)

     1  // Inferno's libkern/memmove-386.s
     2  // https://bitbucket.org/inferno-os/inferno-os/src/default/libkern/memmove-386.s
     3  //
     4  //         Copyright © 1994-1999 Lucent Technologies Inc. All rights reserved.
     5  //         Revisions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com).  All rights reserved.
     6  //         Portions Copyright 2009 The Go Authors. All rights reserved.
     7  //
     8  // Permission is hereby granted, free of charge, to any person obtaining a copy
     9  // of this software and associated documentation files (the "Software"), to deal
    10  // in the Software without restriction, including without limitation the rights
    11  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    12  // copies of the Software, and to permit persons to whom the Software is
    13  // furnished to do so, subject to the following conditions:
    14  //
    15  // The above copyright notice and this permission notice shall be included in
    16  // all copies or substantial portions of the Software.
    17  //
    18  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    19  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    20  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
    21  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    22  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    23  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    24  // THE SOFTWARE.
    25  
    26  #include "textflag.h"
    27  
    28  TEXT runtime·memmove(SB), NOSPLIT, $0-12
    29  	MOVL	to+0(FP), DI
    30  	MOVL	from+4(FP), SI
    31  	MOVL	n+8(FP), BX
    32  
    33  	// REP instructions have a high startup cost, so we handle small sizes
    34  	// with some straightline code. The REP MOVSL instruction is really fast
    35  	// for large sizes. The cutover is approximately 1K.
    36  tail:
    37  	TESTL	BX, BX
    38  	JEQ	move_0
    39  	CMPL	BX, $2
    40  	JBE	move_1or2
    41  	CMPL	BX, $4
    42  	JB	move_3
    43  	JE	move_4
    44  	CMPL	BX, $8
    45  	JBE	move_5through8
    46  	CMPL	BX, $16
    47  	JBE	move_9through16
    48  
    49  /*
    50   * check and set for backwards
    51   */
    52  	CMPL	SI, DI
    53  	JLS	back
    54  
    55  /*
    56   * forward copy loop
    57   */
    58  forward:	
    59  	MOVL	BX, CX
    60  	SHRL	$2, CX
    61  	ANDL	$3, BX
    62  
    63  	REP;	MOVSL
    64  	JMP	tail
    65  /*
    66   * check overlap
    67   */
    68  back:
    69  	MOVL	SI, CX
    70  	ADDL	BX, CX
    71  	CMPL	CX, DI
    72  	JLS	forward
    73  /*
    74   * whole thing backwards has
    75   * adjusted addresses
    76   */
    77  
    78  	ADDL	BX, DI
    79  	ADDL	BX, SI
    80  	STD
    81  
    82  /*
    83   * copy
    84   */
    85  	MOVL	BX, CX
    86  	SHRL	$2, CX
    87  	ANDL	$3, BX
    88  
    89  	SUBL	$4, DI
    90  	SUBL	$4, SI
    91  	REP;	MOVSL
    92  
    93  	CLD
    94  	ADDL	$4, DI
    95  	ADDL	$4, SI
    96  	SUBL	BX, DI
    97  	SUBL	BX, SI
    98  	JMP	tail
    99  
   100  move_1or2:
   101  	MOVB	(SI), AX
   102  	MOVB	-1(SI)(BX*1), CX
   103  	MOVB	AX, (DI)
   104  	MOVB	CX, -1(DI)(BX*1)
   105  	RET
   106  move_0:
   107  	RET
   108  move_3:
   109  	MOVW	(SI), AX
   110  	MOVB	2(SI), CX
   111  	MOVW	AX, (DI)
   112  	MOVB	CX, 2(DI)
   113  	RET
   114  move_4:
   115  	// We need a separate case for 4 to make sure we write pointers atomically.
   116  	MOVL	(SI), AX
   117  	MOVL	AX, (DI)
   118  	RET
   119  move_5through8:
   120  	MOVL	(SI), AX
   121  	MOVL	-4(SI)(BX*1), CX
   122  	MOVL	AX, (DI)
   123  	MOVL	CX, -4(DI)(BX*1)
   124  	RET
   125  move_9through16:
   126  	MOVL	(SI), AX
   127  	MOVL	4(SI), CX
   128  	MOVL	-8(SI)(BX*1), DX
   129  	MOVL	-4(SI)(BX*1), BP
   130  	MOVL	AX, (DI)
   131  	MOVL	CX, 4(DI)
   132  	MOVL	DX, -8(DI)(BX*1)
   133  	MOVL	BP, -4(DI)(BX*1)
   134  	RET