Implementation of strcmp with pcmpistri

fstrcmp.s

	.text
	.globl fstrcmp
	.type	fstrcmp, @function
fstrcmp:
	# If the address is already aligned, skip
	testb $15, %dil
	jz 1f

	# If the first string is empty, quit
	movsbl (%rdi), %edx
	testb %dl, %dl
	jnz 2f
	movsbl (%rsi), %eax
	negl %eax
	ret
2:
	movsbl (%rsi), %ecx
3:
	# Compare bytes until we get to an aligned address
	# If the difference is found, the function returns
	movl %edx, %eax
	subl %ecx, %eax
	jne 3f
	test $15, %dil
	jz 1f
	test %dl, %dl
	jnz 4f
	ret
4:
	# Fetch next chars
	addq $1, %rsi
	addq $1, %rdi
	movsbl (%rdi), %edx
	movsbl (%rsi), %ecx
	jmp 3b
3:
	# Unaligned end
	test $15, %dil
	jz 1f
	ret
1:
	xorl %eax, %eax
	xorq %rcx, %rcx

	movaps (%rdi), %xmm0
	pcmpistri $0x12, (%rsi), %xmm0
	ja 5f
	jc 7f
5:
	addq $16, %rsi
	addq $16, %rdi
	movaps (%rdi), %xmm0
	pcmpistri $0x12, (%rsi), %xmm0
	ja 5b
	jc 7f
6:
	xorl %eax, %eax
	ret
7:
	movsbl (%rdi,%rcx,1), %eax
	movsbl (%rsi,%rcx,1), %ecx
	subl %ecx, %eax
	ret