github.com/hikaru7719/go@v0.0.0-20181025140707-c8b2ac68906a/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.
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    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  // func memmove(to, from unsafe.Pointer, n uintptr)
    29  TEXT runtime·memmove(SB), NOSPLIT, $0-12
    30  	MOVL	to+0(FP), DI
    31  	MOVL	from+4(FP), SI
    32  	MOVL	n+8(FP), BX
    33  
    34  	// REP instructions have a high startup cost, so we handle small sizes
    35  	// with some straightline code. The REP MOVSL instruction is really fast
    36  	// for large sizes. The cutover is approximately 1K.
    37  tail:
    38  	TESTL	BX, BX
    39  	JEQ	move_0
    40  	CMPL	BX, $2
    41  	JBE	move_1or2
    42  	CMPL	BX, $4
    43  	JB	move_3
    44  	JE	move_4
    45  	CMPL	BX, $8
    46  	JBE	move_5through8
    47  	CMPL	BX, $16
    48  	JBE	move_9through16
    49  
    50  /*
    51   * check and set for backwards
    52   */
    53  	CMPL	SI, DI
    54  	JLS	back
    55  
    56  /*
    57   * forward copy loop
    58   */
    59  forward:
    60  	MOVL	BX, CX
    61  	SHRL	$2, CX
    62  	ANDL	$3, BX
    63  
    64  	REP;	MOVSL
    65  	JMP	tail
    66  /*
    67   * check overlap
    68   */
    69  back:
    70  	MOVL	SI, CX
    71  	ADDL	BX, CX
    72  	CMPL	CX, DI
    73  	JLS	forward
    74  /*
    75   * whole thing backwards has
    76   * adjusted addresses
    77   */
    78  
    79  	ADDL	BX, DI
    80  	ADDL	BX, SI
    81  	STD
    82  
    83  /*
    84   * copy
    85   */
    86  	MOVL	BX, CX
    87  	SHRL	$2, CX
    88  	ANDL	$3, BX
    89  
    90  	SUBL	$4, DI
    91  	SUBL	$4, SI
    92  	REP;	MOVSL
    93  
    94  	CLD
    95  	ADDL	$4, DI
    96  	ADDL	$4, SI
    97  	SUBL	BX, DI
    98  	SUBL	BX, SI
    99  	JMP	tail
   100  
   101  move_1or2:
   102  	MOVB	(SI), AX
   103  	MOVB	-1(SI)(BX*1), CX
   104  	MOVB	AX, (DI)
   105  	MOVB	CX, -1(DI)(BX*1)
   106  	RET
   107  move_0:
   108  	RET
   109  move_3:
   110  	MOVW	(SI), AX
   111  	MOVB	2(SI), CX
   112  	MOVW	AX, (DI)
   113  	MOVB	CX, 2(DI)
   114  	RET
   115  move_4:
   116  	// We need a separate case for 4 to make sure we write pointers atomically.
   117  	MOVL	(SI), AX
   118  	MOVL	AX, (DI)
   119  	RET
   120  move_5through8:
   121  	MOVL	(SI), AX
   122  	MOVL	-4(SI)(BX*1), CX
   123  	MOVL	AX, (DI)
   124  	MOVL	CX, -4(DI)(BX*1)
   125  	RET
   126  move_9through16:
   127  	MOVL	(SI), AX
   128  	MOVL	4(SI), CX
   129  	MOVL	-8(SI)(BX*1), DX
   130  	MOVL	-4(SI)(BX*1), BP
   131  	MOVL	AX, (DI)
   132  	MOVL	CX, 4(DI)
   133  	MOVL	DX, -8(DI)(BX*1)
   134  	MOVL	BP, -4(DI)(BX*1)
   135  	RET