overdue

vendor/github.com/pierrec/lz4/decode_amd64.s

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