The Tor Browser / file revision

 # This Source Code Form is subject to the terms of the Mozilla Public

 # License, v. 2.0. If a copy of the MPL was not distributed with this

 # file, You can obtain one at http://mozilla.org/MPL/2.0/.

 # ** ARCFOUR implementation optimized for AMD64.

 # **

 # ** The throughput achieved by this code is about 320 MBytes/sec, on

 # ** a 1.8 GHz AMD Opteron (rev C0) processor.

 .text

 .align 16

 .globl ARCFOUR

 .type ARCFOUR,@function

 ARCFOUR:

 	pushq	%rbp

 	pushq	%rbx

 	movq	%rdi,		%rbp	# key = ARG(key)

 	movq	%rsi,		%rbx	# rbx = ARG(len)

 	movq	%rdx,		%rsi	# in = ARG(in)

 	movq	%rcx,		%rdi	# out = ARG(out)

 	movq	(%rbp),		%rcx	# x = key->x

 	movq	8(%rbp),	%rdx	# y = key->y

 	addq	$16,		%rbp	# d = key->data

 	incq	%rcx			# x++

 	andq	$255,		%rcx	# x &= 0xff

 	leaq	-8(%rbx,%rsi),	%rbx	# rbx = in+len-8

 	movq	%rbx,		%r9	# tmp = in+len-8

 	movq	0(%rbp,%rcx,8),	%rax	# tx = d[x]

 	cmpq	%rsi,		%rbx	# cmp in with in+len-8

 	jl	.Lend			# jump if (in+len-8 < in)

 .Lstart:

 	addq	$8,		%rsi		# increment in

 	addq	$8,		%rdi		# increment out

 	# generate the next 8 bytes of the rc4 stream into %r8

 	movq	$8,		%r11		# byte counter

 1:	addb	%al,		%dl		# y += tx

 	movl	0(%rbp,%rdx,8),	%ebx		# ty = d[y]

 	movl	%ebx,		0(%rbp,%rcx,8)	# d[x] = ty

 	addb	%al,		%bl		# val = ty + tx

 	movl	%eax,		0(%rbp,%rdx,8)	# d[y] = tx

 	incb	%cl				# x++		(NEXT ROUND)

 	movl	0(%rbp,%rcx,8),	%eax		# tx = d[x]	(NEXT ROUND)

 	movb	0(%rbp,%rbx,8),	%r8b		# val = d[val]

 	decb	%r11b

 	rorq	$8,		%r8		# (ror does not change ZF)

 	jnz 	1b

 	# xor 8 bytes

 	xorq	-8(%rsi),	%r8

 	cmpq	%r9,		%rsi		# cmp in+len-8 with in

 	movq	%r8,		-8(%rdi)

 	jle	.Lstart				# jump if (in <= in+len-8)

 .Lend:

 	addq	$8,		%r9		# tmp = in+len

 	# handle the last bytes, one by one

 1:	cmpq	%rsi,		%r9		# cmp in with in+len

 	jle	.Lfinished			# jump if (in+len <= in)

 	addb	%al,		%dl		# y += tx

 	movl	0(%rbp,%rdx,8),	%ebx		# ty = d[y]

 	movl	%ebx,		0(%rbp,%rcx,8)	# d[x] = ty

 	addb	%al,		%bl		# val = ty + tx

 	movl	%eax,		0(%rbp,%rdx,8)	# d[y] = tx

 	incb	%cl				# x++		(NEXT ROUND)

 	movl	0(%rbp,%rcx,8),	%eax		# tx = d[x]	(NEXT ROUND)

 	movb	0(%rbp,%rbx,8),	%r8b		# val = d[val]

 	xorb	(%rsi),		%r8b		# xor 1 byte

 	movb	%r8b,		(%rdi)

 	incq	%rsi				# in++

 	incq	%rdi				# out++

 	jmp 1b

 .Lfinished:

 	decq	%rcx				# x--

 	movb	%dl,		-8(%rbp)	# key->y = y

 	movb	%cl,		-16(%rbp)	# key->x = x

 	popq	%rbx

 	popq	%rbp

 	ret

 .L_ARCFOUR_end:

 .size ARCFOUR,.L_ARCFOUR_end-ARCFOUR

 # Magic indicating no need for an executable stack

 .section .note.GNU-stack,"",@progbits

 .previous