// Copied from S2 implementation.

//go:build !appengine && !noasm && gc && !noasm

#include "textflag.h"

// func matchLen(a []byte, b []byte) int

TEXT ·matchLen(SB), NOSPLIT, $0-56

MOVQ a_base+0(FP), AX

MOVQ b_base+24(FP), CX

MOVQ a_len+8(FP), DX

// matchLen

XORL SI, SI

CMPL DX, $0x08

JB matchlen_match4_standalone

matchlen_loopback_standalone:

MOVQ (AX)(SI*1), BX

XORQ (CX)(SI*1), BX

JZ matchlen_loop_standalone

#ifdef GOAMD64_v3

TZCNTQ BX, BX

#else

BSFQ BX, BX

#endif

SHRL $0x03, BX

LEAL (SI)(BX*1), SI

JMP gen_match_len_end

matchlen_loop_standalone:

LEAL -8(DX), DX

LEAL 8(SI), SI

CMPL DX, $0x08

JAE matchlen_loopback_standalone

matchlen_match4_standalone:

CMPL DX, $0x04

JB matchlen_match2_standalone

MOVL (AX)(SI*1), BX

CMPL (CX)(SI*1), BX

JNE matchlen_match2_standalone

LEAL -4(DX), DX

LEAL 4(SI), SI

matchlen_match2_standalone:

CMPL DX, $0x02

JB matchlen_match1_standalone

MOVW (AX)(SI*1), BX

CMPW (CX)(SI*1), BX

JNE matchlen_match1_standalone

LEAL -2(DX), DX

LEAL 2(SI), SI

matchlen_match1_standalone:

CMPL DX, $0x01

JB gen_match_len_end

MOVB (AX)(SI*1), BL

CMPB (CX)(SI*1), BL

JNE gen_match_len_end

INCL SI

gen_match_len_end:

MOVQ SI, ret+48(FP)

RET