github.com/zebozhuang/go@v0.0.0-20200207033046-f8a98f6f5c5d/src/crypto/rc4/rc4_arm.s (about)

     1  // Copyright 2013 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // +build !nacl
     6  
     7  #include "textflag.h"
     8  
     9  // Registers
    10  #define Rdst	R0
    11  #define Rsrc	R1
    12  #define Rn	R2
    13  #define Rstate	R3
    14  #define Rpi	R4
    15  #define Rpj	R5
    16  #define Ri	R6
    17  #define Rj	R7
    18  #define Rk	R8
    19  #define Rt	R11
    20  #define Rt2	R12
    21  
    22  // func xorKeyStream(dst, src *byte, n int, state *[256]byte, i, j *uint8)
    23  TEXT ·xorKeyStream(SB),NOSPLIT,$0
    24  	MOVW dst+0(FP), Rdst
    25  	MOVW src+4(FP), Rsrc
    26  	MOVW n+8(FP), Rn
    27  	MOVW state+12(FP), Rstate
    28  	MOVW i+16(FP), Rpi
    29  	MOVW j+20(FP), Rpj
    30  	MOVBU (Rpi), Ri
    31  	MOVBU (Rpj), Rj
    32  	MOVW $0, Rk
    33  
    34  loop:
    35  	// i += 1; j += state[i]
    36  	ADD $1, Ri
    37  	AND $0xff, Ri
    38  	MOVBU Ri<<2(Rstate), Rt
    39  	ADD Rt, Rj
    40  	AND $0xff, Rj
    41  
    42  	// swap state[i] <-> state[j]
    43  	MOVBU Rj<<2(Rstate), Rt2
    44  	MOVB Rt2, Ri<<2(Rstate)
    45  	MOVB Rt, Rj<<2(Rstate)
    46  
    47  	// dst[k] = src[k] ^ state[state[i] + state[j]]
    48  	ADD Rt2, Rt
    49  	AND $0xff, Rt
    50  	MOVBU Rt<<2(Rstate), Rt
    51  	MOVBU Rk<<0(Rsrc), Rt2
    52  	EOR Rt, Rt2
    53  	MOVB Rt2, Rk<<0(Rdst)
    54  
    55  	ADD $1, Rk
    56  	CMP Rk, Rn
    57  	BNE loop
    58  
    59  done:
    60  	MOVB Ri, (Rpi)
    61  	MOVB Rj, (Rpj)
    62  	RET