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/*
 * Implement fast CRC32C with PCLMULQDQ instructions. (x86_64)
 *
 * The white papers on CRC32C calculations with PCLMULQDQ instruction can be
 * downloaded from:
 * http://www.intel.com/content/dam/www/public/us/en/documents/white-papers/crc-iscsi-polynomial-crc32-instruction-paper.pdf
 * http://www.intel.com/content/dam/www/public/us/en/documents/white-papers/fast-crc-computation-paper.pdf
 *
 * Copyright (C) 2012 Intel Corporation.
 *
 * Authors:
 *	Wajdi Feghali <wajdi.k.feghali@intel.com>
 *	James Guilford <james.guilford@intel.com>
 *	David Cote <david.m.cote@intel.com>
 *	Tim Chen <tim.c.chen@linux.intel.com>
 *
 * This software is available to you under a choice of one of two
 * licenses.  You may choose to be licensed under the terms of the GNU
 * General Public License (GPL) Version 2, available from the file
 * COPYING in the main directory of this source tree, or the
 * OpenIB.org BSD license below:
 *
 *     Redistribution and use in source and binary forms, with or
 *     without modification, are permitted provided that the following
 *     conditions are met:
 *
 *      - Redistributions of source code must retain the above
 *        copyright notice, this list of conditions and the following
 *        disclaimer.
 *
 *      - Redistributions in binary form must reproduce the above
 *        copyright notice, this list of conditions and the following
 *        disclaimer in the documentation and/or other materials
 *        provided with the distribution.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#include <asm/inst.h>
#include <linux/linkage.h>
#include <asm/nospec-branch.h>

## ISCSI CRC 32 Implementation with crc32 and pclmulqdq Instruction

.macro LABEL prefix n
\prefix\n\():
.endm

.macro JMPTBL_ENTRY i
.word crc_\i - crc_array
.endm

.macro JNC_LESS_THAN j
	jnc less_than_\j
.endm

# Define threshold where buffers are considered "small" and routed to more
# efficient "by-1" code. This "by-1" code only handles up to 255 bytes, so
# SMALL_SIZE can be no larger than 255.

#define SMALL_SIZE 200

.if (SMALL_SIZE > 255)
.error "SMALL_ SIZE must be < 256"
.endif

# unsigned int crc_pcl(u8 *buffer, int len, unsigned int crc_init);

.text
ENTRY(crc_pcl)
#define    bufp		%rdi
#define    bufp_dw	%edi
#define    bufp_w	%di
#define    bufp_b	%dil
#define    bufptmp	%rcx
#define    block_0	%rcx
#define    block_1	%rdx
#define    block_2	%r11
#define    len		%rsi
#define    len_dw	%esi
#define    len_w	%si
#define    len_b	%sil
#define    crc_init_arg %rdx
#define    tmp		%rbx
#define    crc_init	%r8
#define    crc_init_dw	%r8d
#define    crc1		%r9
#define    crc2		%r10

	pushq   %rbx
	pushq   %rdi
	pushq   %rsi

	## Move crc_init for Linux to a different
	mov     crc_init_arg, crc_init

	################################################################
	## 1) ALIGN:
	################################################################

	mov     bufp, bufptmp		# rdi = *buf
	neg     bufp
	and     $7, bufp		# calculate the unalignment amount of
					# the address
	je      proc_block		# Skip if aligned

	## If len is less than 8 and we're unaligned, we need to jump
	## to special code to avoid reading beyond the end of the buffer
	cmp     $8, len
	jae     do_align
	# less_than_8 expects length in upper 3 bits of len_dw
	# less_than_8_post_shl1 expects length = carryflag * 8 + len_dw[31:30]
	shl     $32-3+1, len_dw
	jmp     less_than_8_post_shl1

do_align:
	#### Calculate CRC of unaligned bytes of the buffer (if any)
	movq    (bufptmp), tmp		# load a quadward from the buffer
	add     bufp, bufptmp		# align buffer pointer for quadword
					# processing
	sub     bufp, len		# update buffer length
align_loop:
	crc32b  %bl, crc_init_dw 	# compute crc32 of 1-byte
	shr     $8, tmp			# get next byte
	dec     bufp
	jne     align_loop

proc_block:

	################################################################
	## 2) PROCESS  BLOCKS:
	################################################################

	## compute num of bytes to be processed
	movq    len, tmp		# save num bytes in tmp

	cmpq    $128*24, len
	jae     full_block

continue_block:
	cmpq    $SMALL_SIZE, len
	jb      small

	## len < 128*24
	movq    $2731, %rax		# 2731 = ceil(2^16 / 24)
	mul     len_dw
	shrq    $16, %rax

	## eax contains floor(bytes / 24) = num 24-byte chunks to do

	## process rax 24-byte chunks (128 >= rax >= 0)

	## compute end address of each block
	## block 0 (base addr + RAX * 8)
	## block 1 (base addr + RAX * 16)
	## block 2 (base addr + RAX * 24)
	lea     (bufptmp, %rax, 8), block_0
	lea     (block_0, %rax, 8), block_1
	lea     (block_1, %rax, 8), block_2

	xor     crc1, crc1
	xor     crc2, crc2

	## branch into array
	lea	jump_table(%rip), bufp
	movzxw  (bufp, %rax, 2), len
	lea	crc_array(%rip), bufp
	lea     (bufp, len, 1), bufp
	JMP_NOSPEC bufp

	################################################################
	## 2a) PROCESS FULL BLOCKS:
	################################################################
full_block:
	movl    $128,%eax
	lea     128*8*2(block_0), block_1
	lea     128*8*3(block_0), block_2
	add     $128*8*1, block_0

	xor     crc1,crc1
	xor     crc2,crc2

	# Fall thruogh into top of crc array (crc_128)

	################################################################
	## 3) CRC Array:
	################################################################

crc_array:
	i=128
.rept 128-1
.altmacro
LABEL crc_ %i
.noaltmacro
	crc32q   -i*8(block_0), crc_init
	crc32q   -i*8(block_1), crc1
	crc32q   -i*8(block_2), crc2
	i=(i-1)
.endr

.altmacro
LABEL crc_ %i
.noaltmacro
	crc32q   -i*8(block_0), crc_init
	crc32q   -i*8(block_1), crc1
# SKIP  crc32  -i*8(block_2), crc2 ; Don't do this one yet

	mov     block_2, block_0

	################################################################
	## 4) Combine three results:
	################################################################

	lea	(K_table-8)(%rip), bufp		# first entry is for idx 1
	shlq    $3, %rax			# rax *= 8
	pmovzxdq (bufp,%rax), %xmm0		# 2 consts: K1:K2
	leal	(%eax,%eax,2), %eax		# rax *= 3 (total *24)
	subq    %rax, tmp			# tmp -= rax*24

	movq    crc_init, %xmm1			# CRC for block 1
	PCLMULQDQ 0x00,%xmm0,%xmm1		# Multiply by K2

	movq    crc1, %xmm2			# CRC for block 2
	PCLMULQDQ 0x10, %xmm0, %xmm2		# Multiply by K1

	pxor    %xmm2,%xmm1
	movq    %xmm1, %rax
	xor     -i*8(block_2), %rax
	mov     crc2, crc_init
	crc32   %rax, crc_init

	################################################################
	## 5) Check for end:
	################################################################

LABEL crc_ 0
	mov     tmp, len
	cmp     $128*24, tmp
	jae     full_block
	cmp     $24, tmp
	jae     continue_block

less_than_24:
	shl     $32-4, len_dw			# less_than_16 expects length
						# in upper 4 bits of len_dw
	jnc     less_than_16
	crc32q  (bufptmp), crc_init
	crc32q  8(bufptmp), crc_init
	jz      do_return
	add     $16, bufptmp
	# len is less than 8 if we got here
	# less_than_8 expects length in upper 3 bits of len_dw
	# less_than_8_post_shl1 expects length = carryflag * 8 + len_dw[31:30]
	shl     $2, len_dw
	jmp     less_than_8_post_shl1

	#######################################################################
	## 6) LESS THAN 256-bytes REMAIN AT THIS POINT (8-bits of len are full)
	#######################################################################
small:
	shl $32-8, len_dw		# Prepare len_dw for less_than_256
	j=256
.rept 5					# j = {256, 128, 64, 32, 16}
.altmacro
LABEL less_than_ %j			# less_than_j: Length should be in
					# upper lg(j) bits of len_dw
	j=(j/2)
	shl     $1, len_dw		# Get next MSB
	JNC_LESS_THAN %j
.noaltmacro
	i=0
.rept (j/8)
	crc32q  i(bufptmp), crc_init	# Compute crc32 of 8-byte data
	i=i+8
.endr
	jz      do_return		# Return if remaining length is zero
	add     $j, bufptmp		# Advance buf
.endr

less_than_8:				# Length should be stored in
					# upper 3 bits of len_dw
	shl     $1, len_dw
less_than_8_post_shl1:
	jnc     less_than_4
	crc32l  (bufptmp), crc_init_dw	# CRC of 4 bytes
	jz      do_return		# return if remaining data is zero
	add     $4, bufptmp
less_than_4:				# Length should be stored in
					# upper 2 bits of len_dw
	shl     $1, len_dw
	jnc     less_than_2
	crc32w  (bufptmp), crc_init_dw	# CRC of 2 bytes
	jz      do_return		# return if remaining data is zero
	add     $2, bufptmp
less_than_2:				# Length should be stored in the MSB
					# of len_dw
	shl     $1, len_dw
	jnc     less_than_1
	crc32b  (bufptmp), crc_init_dw	# CRC of 1 byte
less_than_1:				# Length should be zero
do_return:
	movq    crc_init, %rax
	popq    %rsi
	popq    %rdi
	popq    %rbx
        ret
ENDPROC(crc_pcl)

.section	.rodata, "a", @progbits
        ################################################################
        ## jump table        Table is 129 entries x 2 bytes each
        ################################################################
.align 4
jump_table:
	i=0
.rept 129
.altmacro
JMPTBL_ENTRY %i
.noaltmacro
	i=i+1
.endr


	################################################################
	## PCLMULQDQ tables
	## Table is 128 entries x 2 words (8 bytes) each
	################################################################
.align 8
K_table:
	.long 0x493c7d27, 0x00000001
	.long 0xba4fc28e, 0x493c7d27
	.long 0xddc0152b, 0xf20c0dfe
	.long 0x9e4addf8, 0xba4fc28e
	.long 0x39d3b296, 0x3da6d0cb
	.long 0x0715ce53, 0xddc0152b
	.long 0x47db8317, 0x1c291d04
	.long 0x0d3b6092, 0x9e4addf8
	.long 0xc96cfdc0, 0x740eef02
	.long 0x878a92a7, 0x39d3b296
	.long 0xdaece73e, 0x083a6eec
	.long 0xab7aff2a, 0x0715ce53
	.long 0x2162d385, 0xc49f4f67
	.long 0x83348832, 0x47db8317
	.long 0x299847d5, 0x2ad91c30
	.long 0xb9e02b86, 0x0d3b6092
	.long 0x18b33a4e, 0x6992cea2
	.long 0xb6dd949b, 0xc96cfdc0
	.long 0x78d9ccb7, 0x7e908048
	.long 0xbac2fd7b, 0x878a92a7
	.long</