lz4_decode_armv7NEON.s [plain text]
/*
* Copyright (c) 2017 Apple Inc. All rights reserved.
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*
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*/
#include <vm/lz4_assembly_select.h>
#if LZ4_ENABLE_ASSEMBLY_DECODE_ARMV7
/*
int64_t lz4_decode_asm(
uint8_t ** dst_ptr, *dst_ptr points to next output byte to write
uint8_t * dst_begin, points to first valid output byte we can access, dst_begin <= dst
uint8_t * dst_end, "relaxed" end of output buffer (see below)
const uint8_t ** src_ptr, *src_ptr points to next input byte to read
const uint8_t * src_end) "relaxed" end of input buffer (see below)
We test the position of the pointers only to ensure we don't access past src_end/dst_end + some fixed constant.
We never read before dst_begin.
Return 0 on success, -1 on failure
On output, (*src_ptr,*dst_ptr) receives the last position in both buffers corresponding to the beginning of a LZ4 instruction.
*/
.globl _lz4_decode_asm
#define dst r0 // arg0
#define dst_begin r1 // arg1
#define dst_end r2 // arg2
#define src r3 // arg3
#define src_end r4 // arg4
#define n_matches r5
#define n_literals r10
#define copy_src r11 // match/literal copy source
#define copy_dst r8 // match/literal copy destination
#define aux1 r9
#define match_distance r6
#define match_permtable r12
#define match_disttable lr
#define dst_good [sp, #0]
#define src_good [sp, #4]
.macro establish_frame
ldr ip, [sp, #0] // read src_end
push {r4-r7, lr} // Save registers
add r7, sp, #12 // Establish stack frame
push {r8-r11}
mov src_end, ip
push {r0, r3} // save dst/src
sub sp, sp, #4+16 // 4 for 16-byte stack alignment, extra 16-bytes for local
.endm
.macro clear_frame_and_return
add sp, sp, #12+16 // skip r0/r3
pop {r8-r11}
pop {r4-r7,pc}
.endm
// copy_1x16 SOURCE_ADDR DESTINATION_ADDR
// Copy 16 bytes, clobber: q0
.macro copy_1x16
vld1.8 {q0}, [$0]
vst1.8 {q0}, [$1]
.endm
// copy_1x16_and_increment SOURCE_ADDR DESTINATION_ADDR
// Copy 16 bytes, and increment both addresses by 16, clobber: q0
.macro copy_1x16_and_increment
vld1.8 {q0}, [$0]!
vst1.8 {q0}, [$1]!
.endm
// copy_2x16_and_increment SOURCE_ADDR DESTINATION_ADDR
// Copy 2 times 16 bytes, and increment both addresses by 32, clobber: q0
.macro copy_2x16_and_increment
vld1.8 {q0}, [$0]!
vst1.8 {q0}, [$1]!
vld1.8 {q0}, [$0]!
vst1.8 {q0}, [$1]!
.endm
// copy_1x32_and_increment SOURCE_ADDR DESTINATION_ADDR
// Copy 32 bytes, and increment both addresses by 32, clobber: q0,q1
.macro copy_1x32_and_increment
vld1.8 {q0,q1}, [$0]!
vst1.8 {q0,q1}, [$1]!
.endm
// If we don't branch, src < src_end after this
.macro check_src_end
cmp src,src_end
bhs L_done // extremely unlikely, DONE when src >= src_end
.endm
// If we don't branch, dst < dst_end after this
.macro check_dst_end
cmp dst,dst_end
bhs L_done // extremely unlikely, DONE when dst >= dst_end
.endm
.text
.syntax unified
.thumb
.thumb_func _lz4_decode_asm
.p2align 1
_lz4_decode_asm:
establish_frame
ldr src,[src] // src = *src_ptr
ldr dst,[dst] // dst = *dst_ptr
adr match_permtable,L_match_permtable
adr match_disttable,L_match_disttable
L_decode_command:
// Keep last known good positions in both streams
str dst, dst_good
str src, src_good
// Check limits
check_src_end
check_dst_end
// Decode 1-byte command
ldrb aux1,[src],#1 // read command byte LLLLMMMM
lsr n_literals,aux1,#4 // 0000LLLL. n_literals is now 0..15
and n_matches,aux1,#0xf // 0000MMMM. n_matches is now 0..15
add n_matches,n_matches,#4 // n_matches is now 4..19
// Test number of literals (do not test if n_literals==0, because branch prediction fails on it)
cmp n_literals,#14
bls L_copy_short_literal // 96% likely: n_literals in 0..14
// continue to decode_long_literal
// the number of literals is encoded on more bytes, we need to decode them
L_decode_long_literal:
check_src_end // required here, since we may loop an arbitrarily high number of times
ldrb aux1,[src],#1
add n_literals,n_literals,aux1
cmp aux1,#255
beq L_decode_long_literal // extremely unlikely
// continue to copy_long_literal
// Copy literals, n_literals >= 15
L_copy_long_literal:
mov copy_src,src // literal copy origin
mov copy_dst,dst // literal copy destination
add src,src,n_literals
add dst,dst,n_literals
check_src_end // required here, since n_literals can be arbitrarily high
check_dst_end
// fixed + loop
copy_1x32_and_increment copy_src,copy_dst
L_copy_long_literal_loop:
copy_1x32_and_increment copy_src,copy_dst
cmp dst,copy_dst
bhi L_copy_long_literal_loop // first test occurs after 64 bytes have been copied, and is unlikely to loop back
b L_expand_match
// Copy literals, n_literals <= 14: copy 16 bytes
L_copy_short_literal:
copy_1x16 src,dst
add src,src,n_literals
add dst,dst,n_literals
// continue to expand match
L_expand_match:
// Decode match distance
ldrh match_distance,[src],#2 // 16-bit distance
cbz match_distance,L_fail // distance == 0 is invalid
sub copy_src,dst,match_distance // copy_src is the match copy source
cmp copy_src,dst_begin
blo L_fail // copy_src < dst_begin: FAIL
mov copy_dst,dst // copy_dst is the match copy destination
add dst,dst,n_matches // dst is updated to be the byte after the match // Do we need to decode a long match?
cmp n_matches,#19
beq L_decode_long_match // unlikely, n_matches >= 19 encoded on more bytes
cmp n_matches,#16
bhi L_long_match // unlikely, n_matches == 17 or 18
// continue to short match (most probable case)
// Copy match, n_matches <= 16
L_short_match:
cmp match_distance,#15
bls L_copy_short_match_small_distance
// Copy match, n_matches <= 16, match_distance >= 16: copy 16 bytes
copy_1x16 copy_src,copy_dst
b L_decode_command
L_fail:
mov aux1,#-1 // FAIL
b L_exit
L_done:
mov aux1,#0 // OK
// continue to L_exit
L_exit:
ldr dst,[sp, #20] // get back src_ptr,dst_ptr from stack
ldr src,[sp, #24] // get back src_ptr,dst_ptr from stack
ldr ip, src_good
ldr lr, dst_good
str ip,[src] // *src_ptr = src_good
str lr,[dst] // *dst_ptr = dst_good
mov r0,aux1 // x0 = return value
clear_frame_and_return
// Copy match, n_matches <= 16, match_distance < 16:
// load shuffle table, and permute to replicate the pattern on 16 bytes
L_copy_short_match_small_distance:
vld1.8 {q0},[copy_src]
add aux1,match_permtable,match_distance,lsl #5 // index in table
vld1.8 {q1},[aux1] // load only permutation for the low 16 bytes
vtbl.8 d4, {q0}, d2 // low 16 bytes of pattern
vtbl.8 d5, {q0}, d3 // low 16 bytes of pattern
vst1.8 {q2},[copy_dst]
b L_decode_command
// n_matches == 19: the number of matches in encoded on more bytes, we need to decode them
L_decode_long_match:
check_src_end // required here, since we may loop an arbitrarily high number of times
ldrb aux1,[src],#1
add dst,dst,aux1
cmp aux1,#255
beq L_decode_long_match // very unlikely
check_dst_end // required here, since dst was incremented by a arbitrarily high value
// continue to long_match
// n_matches > 16
L_long_match:
cmp match_distance,#31
bhi L_copy_long_match_32
cmp match_distance,#15
bhi L_copy_long_match_16
// Copy match, n_matches >= 16, match_distance < 16:
// load shuffle table, and permute to replicate the pattern on 32 bytes
L_copy_long_match_small_distance:
vld1.8 {q1}, [copy_src] // 16 pattern bytes
add aux1,match_permtable,match_distance,lsl #5 // index in table
vld1.8 {q2-q3}, [aux1] // load 32-byte permutation
vtbl.8 d4, {q1}, d4 // low 16 bytes of pattern
vtbl.8 d5, {q1}, d5 // low 16 bytes of pattern
vtbl.8 d6, {q1}, d6 // low 16 bytes of pattern
vtbl.8 d7, {q1}, d7 // low 16 bytes of pattern
ldrb aux1,[match_disttable,match_distance] // valid pattern length in aux1
// fixed
vst1.8 {q2-q3},[copy_dst]
add copy_dst,copy_dst,aux1
L_copy_long_match_small_distance_loop:
// loop
vst1.8 {q2-q3},[copy_dst]
add copy_dst,copy_dst,aux1
vst1.8 {q2-q3},[copy_dst]
add copy_dst,copy_dst,aux1
cmp dst,copy_dst
bhi L_copy_long_match_small_distance_loop
b L_decode_command
// Copy match, n_matches >= 16, match_distance >= 32
L_copy_long_match_32:
// fixed + loop
copy_1x16_and_increment copy_src,copy_dst
L_copy_long_match_32_loop:
copy_1x32_and_increment copy_src,copy_dst
cmp dst,copy_dst
bhi L_copy_long_match_32_loop
b L_decode_command
// Copy match, n_matches >= 16, match_distance >= 16
L_copy_long_match_16:
// fixed + loop
copy_1x16_and_increment copy_src,copy_dst
L_copy_long_match_16_loop:
copy_2x16_and_increment copy_src,copy_dst
cmp dst,copy_dst
bhi L_copy_long_match_16_loop
b L_decode_command
// permutation tables for short distance matches, 32 byte result, for match_distance = 0 to 15
// value(d)[i] = i%d for i = 0..31
.p2align 6
L_match_permtable:
.byte 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 // 0
.byte 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 // 1
.byte 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1 // 2
.byte 0, 1, 2, 0, 1, 2, 0, 1, 2, 0, 1, 2, 0, 1, 2, 0, 1, 2, 0, 1, 2, 0, 1, 2, 0, 1, 2, 0, 1, 2, 0, 1 // 3
.byte 0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3 // 4
.byte 0, 1, 2, 3, 4, 0, 1, 2, 3, 4, 0, 1, 2, 3, 4, 0, 1, 2, 3, 4, 0, 1, 2, 3, 4, 0, 1, 2, 3, 4, 0, 1 // 5
.byte 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 0, 1 // 6
.byte 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3 // 7
.byte 0, 1, 2, 3, 4, 5, 6, 7, 0, 1, 2, 3, 4, 5, 6, 7, 0, 1, 2, 3, 4, 5, 6, 7, 0, 1, 2, 3, 4, 5, 6, 7 // 8
.byte 0, 1, 2, 3, 4, 5, 6, 7, 8, 0, 1, 2, 3, 4, 5, 6, 7, 8, 0, 1, 2, 3, 4, 5, 6, 7, 8, 0, 1, 2, 3, 4 // 9
.byte 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1 // 10
.byte 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 // 11
.byte 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,10,11, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,10,11, 0, 1, 2, 3, 4, 5, 6, 7 // 12
.byte 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,10,11,12, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,10,11,12, 0, 1, 2, 3, 4, 5 // 13
.byte 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,10,11,12,13, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,10,11,12,13, 0, 1, 2, 3 // 14
.byte 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,10,11,12,13,14, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,10,11,12,13,14, 0, 1 // 15
// valid repeating pattern size, for each match_distance = 0 to 15
// value(d) = 32 - (32%d), is the largest a multiple of d <= 32
.p2align 6
L_match_disttable:
.byte 32,32,32,30 // 0 .. 3
.byte 16,30,30,28 // 4 .. 7
.byte 16,27,30,22 // 8 .. 11
.byte 24,26,28,30 // 12 .. 15
#endif // LZ4_ENABLE_ASSEMBLY_DECODE_ARMV7