github.com/twelsh-aw/go/src@v0.0.0-20230516233729-a56fe86a7c81/runtime/memmove_plan9_amd64.s (about)

     1  // Derived from Inferno's libkern/memmove-386.s (adapted for amd64)
     2  // https://bitbucket.org/inferno-os/inferno-os/src/master/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  // See memmove Go doc for important implementation constraints.
    29  
    30  // func memmove(to, from unsafe.Pointer, n uintptr)
    31  TEXT runtime·memmove(SB), NOSPLIT, $0-24
    32  
    33  	MOVQ	to+0(FP), DI
    34  	MOVQ	from+8(FP), SI
    35  	MOVQ	n+16(FP), BX
    36  
    37  	// REP instructions have a high startup cost, so we handle small sizes
    38  	// with some straightline code. The REP MOVSQ instruction is really fast
    39  	// for large sizes. The cutover is approximately 1K.
    40  tail:
    41  	TESTQ	BX, BX
    42  	JEQ	move_0
    43  	CMPQ	BX, $2
    44  	JBE	move_1or2
    45  	CMPQ	BX, $4
    46  	JBE	move_3or4
    47  	CMPQ	BX, $8
    48  	JB	move_5through7
    49  	JE	move_8
    50  	CMPQ	BX, $16
    51  	JBE	move_9through16
    52  
    53  /*
    54   * check and set for backwards
    55   */
    56  	CMPQ	SI, DI
    57  	JLS	back
    58  
    59  /*
    60   * forward copy loop
    61   */
    62  forward:
    63  	MOVQ	BX, CX
    64  	SHRQ	$3, CX
    65  	ANDQ	$7, BX
    66  
    67  	REP;	MOVSQ
    68  	JMP	tail
    69  
    70  back:
    71  /*
    72   * check overlap
    73   */
    74  	MOVQ	SI, CX
    75  	ADDQ	BX, CX
    76  	CMPQ	CX, DI
    77  	JLS	forward
    78  
    79  /*
    80   * whole thing backwards has
    81   * adjusted addresses
    82   */
    83  	ADDQ	BX, DI
    84  	ADDQ	BX, SI
    85  	STD
    86  
    87  /*
    88   * copy
    89   */
    90  	MOVQ	BX, CX
    91  	SHRQ	$3, CX
    92  	ANDQ	$7, BX
    93  
    94  	SUBQ	$8, DI
    95  	SUBQ	$8, SI
    96  	REP;	MOVSQ
    97  
    98  	CLD
    99  	ADDQ	$8, DI
   100  	ADDQ	$8, SI
   101  	SUBQ	BX, DI
   102  	SUBQ	BX, SI
   103  	JMP	tail
   104  
   105  move_1or2:
   106  	MOVB	(SI), AX
   107  	MOVB	-1(SI)(BX*1), CX
   108  	MOVB	AX, (DI)
   109  	MOVB	CX, -1(DI)(BX*1)
   110  	RET
   111  move_0:
   112  	RET
   113  move_3or4:
   114  	MOVW	(SI), AX
   115  	MOVW	-2(SI)(BX*1), CX
   116  	MOVW	AX, (DI)
   117  	MOVW	CX, -2(DI)(BX*1)
   118  	RET
   119  move_5through7:
   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_8:
   126  	// We need a separate case for 8 to make sure we write pointers atomically.
   127  	MOVQ	(SI), AX
   128  	MOVQ	AX, (DI)
   129  	RET
   130  move_9through16:
   131  	MOVQ	(SI), AX
   132  	MOVQ	-8(SI)(BX*1), CX
   133  	MOVQ	AX, (DI)
   134  	MOVQ	CX, -8(DI)(BX*1)
   135  	RET