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375 lines
6.0 KiB
375 lines
6.0 KiB
// +build !appengine
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// +build gc
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// +build !noasm
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#include "textflag.h"
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// AX scratch
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// BX scratch
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// CX scratch
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// DX token
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//
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// DI &dst
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// SI &src
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// R8 &dst + len(dst)
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// R9 &src + len(src)
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// R11 &dst
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// R12 short output end
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// R13 short input end
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// func decodeBlock(dst, src []byte) int
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// using 50 bytes of stack currently
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TEXT ·decodeBlock(SB), NOSPLIT, $64-56
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MOVQ dst_base+0(FP), DI
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MOVQ DI, R11
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MOVQ dst_len+8(FP), R8
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ADDQ DI, R8
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MOVQ src_base+24(FP), SI
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MOVQ src_len+32(FP), R9
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ADDQ SI, R9
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// shortcut ends
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// short output end
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MOVQ R8, R12
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SUBQ $32, R12
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// short input end
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MOVQ R9, R13
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SUBQ $16, R13
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loop:
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// for si < len(src)
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CMPQ SI, R9
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JGE end
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// token := uint32(src[si])
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MOVBQZX (SI), DX
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INCQ SI
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// lit_len = token >> 4
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// if lit_len > 0
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// CX = lit_len
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MOVQ DX, CX
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SHRQ $4, CX
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// if lit_len != 0xF
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CMPQ CX, $0xF
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JEQ lit_len_loop_pre
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CMPQ DI, R12
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JGE lit_len_loop_pre
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CMPQ SI, R13
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JGE lit_len_loop_pre
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// copy shortcut
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// A two-stage shortcut for the most common case:
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// 1) If the literal length is 0..14, and there is enough space,
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// enter the shortcut and copy 16 bytes on behalf of the literals
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// (in the fast mode, only 8 bytes can be safely copied this way).
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// 2) Further if the match length is 4..18, copy 18 bytes in a similar
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// manner; but we ensure that there's enough space in the output for
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// those 18 bytes earlier, upon entering the shortcut (in other words,
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// there is a combined check for both stages).
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// copy literal
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MOVOU (SI), X0
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MOVOU X0, (DI)
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ADDQ CX, DI
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ADDQ CX, SI
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MOVQ DX, CX
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ANDQ $0xF, CX
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// The second stage: prepare for match copying, decode full info.
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// If it doesn't work out, the info won't be wasted.
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// offset := uint16(data[:2])
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MOVWQZX (SI), DX
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ADDQ $2, SI
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MOVQ DI, AX
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SUBQ DX, AX
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CMPQ AX, DI
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JGT err_short_buf
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// if we can't do the second stage then jump straight to read the
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// match length, we already have the offset.
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CMPQ CX, $0xF
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JEQ match_len_loop_pre
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CMPQ DX, $8
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JLT match_len_loop_pre
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CMPQ AX, R11
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JLT err_short_buf
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// memcpy(op + 0, match + 0, 8);
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MOVQ (AX), BX
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MOVQ BX, (DI)
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// memcpy(op + 8, match + 8, 8);
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MOVQ 8(AX), BX
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MOVQ BX, 8(DI)
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// memcpy(op +16, match +16, 2);
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MOVW 16(AX), BX
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MOVW BX, 16(DI)
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ADDQ $4, DI // minmatch
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ADDQ CX, DI
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// shortcut complete, load next token
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JMP loop
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lit_len_loop_pre:
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// if lit_len > 0
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CMPQ CX, $0
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JEQ offset
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CMPQ CX, $0xF
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JNE copy_literal
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lit_len_loop:
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// for src[si] == 0xFF
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CMPB (SI), $0xFF
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JNE lit_len_finalise
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// bounds check src[si+1]
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MOVQ SI, AX
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ADDQ $1, AX
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CMPQ AX, R9
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JGT err_short_buf
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// lit_len += 0xFF
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ADDQ $0xFF, CX
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INCQ SI
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JMP lit_len_loop
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lit_len_finalise:
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// lit_len += int(src[si])
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// si++
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MOVBQZX (SI), AX
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ADDQ AX, CX
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INCQ SI
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copy_literal:
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// bounds check src and dst
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MOVQ SI, AX
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ADDQ CX, AX
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CMPQ AX, R9
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JGT err_short_buf
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MOVQ DI, AX
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ADDQ CX, AX
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CMPQ AX, R8
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JGT err_short_buf
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// whats a good cut off to call memmove?
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CMPQ CX, $16
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JGT memmove_lit
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// if len(dst[di:]) < 16
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MOVQ R8, AX
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SUBQ DI, AX
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CMPQ AX, $16
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JLT memmove_lit
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// if len(src[si:]) < 16
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MOVQ R9, AX
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SUBQ SI, AX
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CMPQ AX, $16
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JLT memmove_lit
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MOVOU (SI), X0
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MOVOU X0, (DI)
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JMP finish_lit_copy
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memmove_lit:
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// memmove(to, from, len)
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MOVQ DI, 0(SP)
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MOVQ SI, 8(SP)
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MOVQ CX, 16(SP)
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// spill
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MOVQ DI, 24(SP)
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MOVQ SI, 32(SP)
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MOVQ CX, 40(SP) // need len to inc SI, DI after
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MOVB DX, 48(SP)
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CALL runtime·memmove(SB)
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// restore registers
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MOVQ 24(SP), DI
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MOVQ 32(SP), SI
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MOVQ 40(SP), CX
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MOVB 48(SP), DX
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// recalc initial values
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MOVQ dst_base+0(FP), R8
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MOVQ R8, R11
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ADDQ dst_len+8(FP), R8
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MOVQ src_base+24(FP), R9
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ADDQ src_len+32(FP), R9
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MOVQ R8, R12
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SUBQ $32, R12
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MOVQ R9, R13
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SUBQ $16, R13
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finish_lit_copy:
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ADDQ CX, SI
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ADDQ CX, DI
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CMPQ SI, R9
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JGE end
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offset:
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// CX := mLen
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// free up DX to use for offset
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MOVQ DX, CX
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MOVQ SI, AX
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ADDQ $2, AX
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CMPQ AX, R9
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JGT err_short_buf
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// offset
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// DX := int(src[si]) | int(src[si+1])<<8
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MOVWQZX (SI), DX
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ADDQ $2, SI
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// 0 offset is invalid
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CMPQ DX, $0
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JEQ err_corrupt
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ANDB $0xF, CX
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match_len_loop_pre:
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// if mlen != 0xF
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CMPB CX, $0xF
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JNE copy_match
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match_len_loop:
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// for src[si] == 0xFF
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// lit_len += 0xFF
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CMPB (SI), $0xFF
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JNE match_len_finalise
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// bounds check src[si+1]
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MOVQ SI, AX
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ADDQ $1, AX
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CMPQ AX, R9
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JGT err_short_buf
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ADDQ $0xFF, CX
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INCQ SI
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JMP match_len_loop
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match_len_finalise:
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// lit_len += int(src[si])
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// si++
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MOVBQZX (SI), AX
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ADDQ AX, CX
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INCQ SI
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copy_match:
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// mLen += minMatch
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ADDQ $4, CX
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// check we have match_len bytes left in dst
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// di+match_len < len(dst)
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MOVQ DI, AX
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ADDQ CX, AX
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CMPQ AX, R8
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JGT err_short_buf
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// DX = offset
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// CX = match_len
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// BX = &dst + (di - offset)
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MOVQ DI, BX
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SUBQ DX, BX
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// check BX is within dst
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// if BX < &dst
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CMPQ BX, R11
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JLT err_short_buf
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// if offset + match_len < di
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MOVQ BX, AX
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ADDQ CX, AX
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CMPQ DI, AX
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JGT copy_interior_match
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// AX := len(dst[:di])
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// MOVQ DI, AX
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// SUBQ R11, AX
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// copy 16 bytes at a time
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// if di-offset < 16 copy 16-(di-offset) bytes to di
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// then do the remaining
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copy_match_loop:
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// for match_len >= 0
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// dst[di] = dst[i]
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// di++
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// i++
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MOVB (BX), AX
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MOVB AX, (DI)
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INCQ DI
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INCQ BX
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DECQ CX
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CMPQ CX, $0
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JGT copy_match_loop
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JMP loop
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copy_interior_match:
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CMPQ CX, $16
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JGT memmove_match
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// if len(dst[di:]) < 16
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MOVQ R8, AX
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SUBQ DI, AX
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CMPQ AX, $16
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JLT memmove_match
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MOVOU (BX), X0
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MOVOU X0, (DI)
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ADDQ CX, DI
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JMP loop
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memmove_match:
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// memmove(to, from, len)
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MOVQ DI, 0(SP)
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MOVQ BX, 8(SP)
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MOVQ CX, 16(SP)
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// spill
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MOVQ DI, 24(SP)
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MOVQ SI, 32(SP)
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MOVQ CX, 40(SP) // need len to inc SI, DI after
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CALL runtime·memmove(SB)
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// restore registers
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MOVQ 24(SP), DI
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MOVQ 32(SP), SI
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MOVQ 40(SP), CX
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// recalc initial values
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MOVQ dst_base+0(FP), R8
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MOVQ R8, R11 // TODO: make these sensible numbers
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ADDQ dst_len+8(FP), R8
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MOVQ src_base+24(FP), R9
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ADDQ src_len+32(FP), R9
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MOVQ R8, R12
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SUBQ $32, R12
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MOVQ R9, R13
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SUBQ $16, R13
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ADDQ CX, DI
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JMP loop
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err_corrupt:
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MOVQ $-1, ret+48(FP)
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RET
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err_short_buf:
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MOVQ $-2, ret+48(FP)
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RET
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end:
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SUBQ R11, DI
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MOVQ DI, ret+48(FP)
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RET
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