github.com/ttpreport/gvisor-ligolo@v0.0.0-20240123134145-a858404967ba/pkg/sentry/time/muldiv_amd64.s (about)

     1  // Copyright 2018 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  #include "textflag.h"
    16  
    17  // Documentation is available in parameters.go.
    18  //
    19  // func muldiv64(value, multiplier, divisor uint64) (uint64, bool)
    20  TEXT ·muldiv64(SB),NOSPLIT|NOFRAME,$0-33
    21  	MOVQ value+0(FP), AX
    22  	MOVQ multiplier+8(FP), BX
    23  	MOVQ divisor+16(FP), CX
    24  
    25  	// Multiply AX*BX and store result in DX:AX.
    26  	MULQ BX
    27  
    28  	// If divisor <= (value*multiplier) / 2^64, then the division will overflow.
    29  	//
    30  	// (value*multiplier) / 2^64 is DX:AX >> 64, or simply DX.
    31  	CMPQ CX, DX
    32  	JLE overflow
    33  
    34  	// Divide DX:AX by CX.
    35  	DIVQ CX
    36  
    37  	MOVQ AX, ret+24(FP)
    38  	MOVB $1, ret1+32(FP)
    39  	RET
    40  
    41  overflow:
    42  	MOVQ $0, ret+24(FP)
    43  	MOVB $0, ret1+32(FP)
    44  	RET