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s2: Improve amd64 decompression speed. #436

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merged 2 commits into from Sep 6, 2021
Merged

s2: Improve amd64 decompression speed. #436

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s2: Improve amd64 decompression speed.
klauspost Sep 6, 2021
f81d808
Merge branch 'master' into s2-faster-decompression
klauspost Sep 6, 2021
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37 changes: 17 additions & 20 deletions s2/decode_amd64.s
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Expand Up @@ -227,11 +227,11 @@ tagLit62Plus:

// case x == 62:
// x = uint32(src[s-3]) | uint32(src[s-2])<<8 | uint32(src[s-1])<<16
MOVWLZX -3(R_SRC), R_LEN
MOVBLZX -1(R_SRC), R_TMP1
SHLL $16, R_TMP1
ORL R_TMP1, R_LEN
JMP doLit
// We read one byte, safe to read one back, since we are just reading tag.
// x = binary.LittleEndian.Uint32(src[s-1:]) >> 8
MOVL -4(R_SRC), R_LEN
SHRL $8, R_LEN
JMP doLit

tagLit63:
// case x == 63:
Expand Down Expand Up @@ -294,20 +294,18 @@ tagCopy:
JA errCorrupt

// offset = int(uint32(src[s-2])&0xe0<<3 | uint32(src[s-1]))
// length = 4 + int(src[s-2])>>2&0x7
MOVBQZX -1(R_SRC), R_TMP1
MOVQ R_LEN, R_TMP0
SHRQ $2, R_LEN
ANDQ $0xe0, R_TMP0
ANDQ $7, R_LEN
SHLQ $3, R_TMP0
MOVBQZX -1(R_SRC), R_TMP1
ADDQ $4, R_LEN
ORQ R_TMP1, R_TMP0

// length = 4 + int(src[s-2])>>2&0x7
SHRQ $2, R_LEN
ANDQ $7, R_LEN
ADDQ $4, R_LEN

// check if repeat code
CMPQ R_TMP0, $0
JE repeatCode
// check if repeat code, ZF set by ORQ.
JZ repeatCode

// This is a regular copy, transfer our temporary value to R_OFF (length)
MOVQ R_TMP0, R_OFF
Expand Down Expand Up @@ -363,12 +361,11 @@ repeatLen3:
JA errCorrupt

// length = uint32(src[s-3]) | (uint32(src[s-2])<<8) | (uint32(src[s-1])<<16) + (1 << 16)
MOVBLZX -1(R_SRC), R_TMP0
MOVWLZX -3(R_SRC), R_LEN
SHLL $16, R_TMP0
ORL R_TMP0, R_LEN
ADDL $65540, R_LEN
JMP doCopyRepeat
// Read one byte further back (just part of the tag, shifted out)
MOVL -4(R_SRC), R_LEN
SHRL $8, R_LEN
ADDL $65540, R_LEN
JMP doCopyRepeat

doCopy:
// This is the end of the outer "switch", when we have a copy tag.
Expand Down