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compare_amd64.s
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// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
#include "go_asm.h"
#include "asm_amd64.h"
#include "textflag.h"
TEXT ·Compare<ABIInternal>(SB),NOSPLIT,$0-56
// AX = a_base (want in SI)
// BX = a_len (want in BX)
// CX = a_cap (unused)
// DI = b_base (want in DI)
// SI = b_len (want in DX)
// R8 = b_cap (unused)
MOVQ SI, DX
MOVQ AX, SI
JMP cmpbody<>(SB)
TEXT runtime·cmpstring<ABIInternal>(SB),NOSPLIT,$0-40
// AX = a_base (want in SI)
// BX = a_len (want in BX)
// CX = b_base (want in DI)
// DI = b_len (want in DX)
MOVQ AX, SI
MOVQ DI, DX
MOVQ CX, DI
JMP cmpbody<>(SB)
// input:
// SI = a
// DI = b
// BX = alen
// DX = blen
// output:
// AX = output (-1/0/1)
TEXT cmpbody<>(SB),NOSPLIT,$0-0
CMPQ SI, DI
JEQ allsame
CMPQ BX, DX
MOVQ DX, R8
CMOVQLT BX, R8 // R8 = min(alen, blen) = # of bytes to compare
CMPQ R8, $8
JB small
CMPQ R8, $63
JBE loop
#ifndef hasAVX2
CMPB internal∕cpu·X86+const_offsetX86HasAVX2(SB), $1
JEQ big_loop_avx2
JMP big_loop
#else
JMP big_loop_avx2
#endif
loop:
CMPQ R8, $16
JBE _0through16
MOVOU (SI), X0
MOVOU (DI), X1
PCMPEQB X0, X1
PMOVMSKB X1, AX
XORQ $0xffff, AX // convert EQ to NE
JNE diff16 // branch if at least one byte is not equal
ADDQ $16, SI
ADDQ $16, DI
SUBQ $16, R8
JMP loop
diff64:
ADDQ $48, SI
ADDQ $48, DI
JMP diff16
diff48:
ADDQ $32, SI
ADDQ $32, DI
JMP diff16
diff32:
ADDQ $16, SI
ADDQ $16, DI
// AX = bit mask of differences
diff16:
BSFQ AX, BX // index of first byte that differs
XORQ AX, AX
MOVB (SI)(BX*1), CX
CMPB CX, (DI)(BX*1)
SETHI AX
LEAQ -1(AX*2), AX // convert 1/0 to +1/-1
RET
// 0 through 16 bytes left, alen>=8, blen>=8
_0through16:
CMPQ R8, $8
JBE _0through8
MOVQ (SI), AX
MOVQ (DI), CX
CMPQ AX, CX
JNE diff8
_0through8:
MOVQ -8(SI)(R8*1), AX
MOVQ -8(DI)(R8*1), CX
CMPQ AX, CX
JEQ allsame
// AX and CX contain parts of a and b that differ.
diff8:
BSWAPQ AX // reverse order of bytes
BSWAPQ CX
XORQ AX, CX
BSRQ CX, CX // index of highest bit difference
SHRQ CX, AX // move a's bit to bottom
ANDQ $1, AX // mask bit
LEAQ -1(AX*2), AX // 1/0 => +1/-1
RET
// 0-7 bytes in common
small:
LEAQ (R8*8), CX // bytes left -> bits left
NEGQ CX // - bits lift (== 64 - bits left mod 64)
JEQ allsame
// load bytes of a into high bytes of AX
CMPB SI, $0xf8
JA si_high
MOVQ (SI), SI
JMP si_finish
si_high:
MOVQ -8(SI)(R8*1), SI
SHRQ CX, SI
si_finish:
SHLQ CX, SI
// load bytes of b in to high bytes of BX
CMPB DI, $0xf8
JA di_high
MOVQ (DI), DI
JMP di_finish
di_high:
MOVQ -8(DI)(R8*1), DI
SHRQ CX, DI
di_finish:
SHLQ CX, DI
BSWAPQ SI // reverse order of bytes
BSWAPQ DI
XORQ SI, DI // find bit differences
JEQ allsame
BSRQ DI, CX // index of highest bit difference
SHRQ CX, SI // move a's bit to bottom
ANDQ $1, SI // mask bit
LEAQ -1(SI*2), AX // 1/0 => +1/-1
RET
allsame:
XORQ AX, AX
XORQ CX, CX
CMPQ BX, DX
SETGT AX // 1 if alen > blen
SETEQ CX // 1 if alen == blen
LEAQ -1(CX)(AX*2), AX // 1,0,-1 result
RET
// this works for >= 64 bytes of data.
#ifndef hasAVX2
big_loop:
MOVOU (SI), X0
MOVOU (DI), X1
PCMPEQB X0, X1
PMOVMSKB X1, AX
XORQ $0xffff, AX
JNE diff16
MOVOU 16(SI), X0
MOVOU 16(DI), X1
PCMPEQB X0, X1
PMOVMSKB X1, AX
XORQ $0xffff, AX
JNE diff32
MOVOU 32(SI), X0
MOVOU 32(DI), X1
PCMPEQB X0, X1
PMOVMSKB X1, AX
XORQ $0xffff, AX
JNE diff48
MOVOU 48(SI), X0
MOVOU 48(DI), X1
PCMPEQB X0, X1
PMOVMSKB X1, AX
XORQ $0xffff, AX
JNE diff64
ADDQ $64, SI
ADDQ $64, DI
SUBQ $64, R8
CMPQ R8, $64
JBE loop
JMP big_loop
#endif
// Compare 64-bytes per loop iteration.
// Loop is unrolled and uses AVX2.
big_loop_avx2:
VMOVDQU (SI), Y2
VMOVDQU (DI), Y3
VMOVDQU 32(SI), Y4
VMOVDQU 32(DI), Y5
VPCMPEQB Y2, Y3, Y0
VPMOVMSKB Y0, AX
XORL $0xffffffff, AX
JNE diff32_avx2
VPCMPEQB Y4, Y5, Y6
VPMOVMSKB Y6, AX
XORL $0xffffffff, AX
JNE diff64_avx2
ADDQ $64, SI
ADDQ $64, DI
SUBQ $64, R8
CMPQ R8, $64
JB big_loop_avx2_exit
JMP big_loop_avx2
// Avoid AVX->SSE transition penalty and search first 32 bytes of 64 byte chunk.
diff32_avx2:
VZEROUPPER
JMP diff16
// Same as diff32_avx2, but for last 32 bytes.
diff64_avx2:
VZEROUPPER
JMP diff48
// For <64 bytes remainder jump to normal loop.
big_loop_avx2_exit:
VZEROUPPER
JMP loop