diff options
Diffstat (limited to 'vendor/github.com/golang/snappy/decode_arm64.s')
| -rw-r--r-- | vendor/github.com/golang/snappy/decode_arm64.s | 494 |
1 files changed, 0 insertions, 494 deletions
diff --git a/vendor/github.com/golang/snappy/decode_arm64.s b/vendor/github.com/golang/snappy/decode_arm64.s deleted file mode 100644 index 7a3ead17e..000000000 --- a/vendor/github.com/golang/snappy/decode_arm64.s +++ /dev/null @@ -1,494 +0,0 @@ -// Copyright 2020 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. - -// +build !appengine -// +build gc -// +build !noasm - -#include "textflag.h" - -// The asm code generally follows the pure Go code in decode_other.go, except -// where marked with a "!!!". - -// func decode(dst, src []byte) int -// -// All local variables fit into registers. The non-zero stack size is only to -// spill registers and push args when issuing a CALL. The register allocation: -// - R2 scratch -// - R3 scratch -// - R4 length or x -// - R5 offset -// - R6 &src[s] -// - R7 &dst[d] -// + R8 dst_base -// + R9 dst_len -// + R10 dst_base + dst_len -// + R11 src_base -// + R12 src_len -// + R13 src_base + src_len -// - R14 used by doCopy -// - R15 used by doCopy -// -// The registers R8-R13 (marked with a "+") are set at the start of the -// function, and after a CALL returns, and are not otherwise modified. -// -// The d variable is implicitly R7 - R8, and len(dst)-d is R10 - R7. -// The s variable is implicitly R6 - R11, and len(src)-s is R13 - R6. -TEXT ·decode(SB), NOSPLIT, $56-56 - // Initialize R6, R7 and R8-R13. - MOVD dst_base+0(FP), R8 - MOVD dst_len+8(FP), R9 - MOVD R8, R7 - MOVD R8, R10 - ADD R9, R10, R10 - MOVD src_base+24(FP), R11 - MOVD src_len+32(FP), R12 - MOVD R11, R6 - MOVD R11, R13 - ADD R12, R13, R13 - -loop: - // for s < len(src) - CMP R13, R6 - BEQ end - - // R4 = uint32(src[s]) - // - // switch src[s] & 0x03 - MOVBU (R6), R4 - MOVW R4, R3 - ANDW $3, R3 - MOVW $1, R1 - CMPW R1, R3 - BGE tagCopy - - // ---------------------------------------- - // The code below handles literal tags. - - // case tagLiteral: - // x := uint32(src[s] >> 2) - // switch - MOVW $60, R1 - LSRW $2, R4, R4 - CMPW R4, R1 - BLS tagLit60Plus - - // case x < 60: - // s++ - ADD $1, R6, R6 - -doLit: - // This is the end of the inner "switch", when we have a literal tag. - // - // We assume that R4 == x and x fits in a uint32, where x is the variable - // used in the pure Go decode_other.go code. - - // length = int(x) + 1 - // - // Unlike the pure Go code, we don't need to check if length <= 0 because - // R4 can hold 64 bits, so the increment cannot overflow. - ADD $1, R4, R4 - - // Prepare to check if copying length bytes will run past the end of dst or - // src. - // - // R2 = len(dst) - d - // R3 = len(src) - s - MOVD R10, R2 - SUB R7, R2, R2 - MOVD R13, R3 - SUB R6, R3, R3 - - // !!! Try a faster technique for short (16 or fewer bytes) copies. - // - // if length > 16 || len(dst)-d < 16 || len(src)-s < 16 { - // goto callMemmove // Fall back on calling runtime·memmove. - // } - // - // The C++ snappy code calls this TryFastAppend. It also checks len(src)-s - // against 21 instead of 16, because it cannot assume that all of its input - // is contiguous in memory and so it needs to leave enough source bytes to - // read the next tag without refilling buffers, but Go's Decode assumes - // contiguousness (the src argument is a []byte). - CMP $16, R4 - BGT callMemmove - CMP $16, R2 - BLT callMemmove - CMP $16, R3 - BLT callMemmove - - // !!! Implement the copy from src to dst as a 16-byte load and store. - // (Decode's documentation says that dst and src must not overlap.) - // - // This always copies 16 bytes, instead of only length bytes, but that's - // OK. If the input is a valid Snappy encoding then subsequent iterations - // will fix up the overrun. Otherwise, Decode returns a nil []byte (and a - // non-nil error), so the overrun will be ignored. - // - // Note that on arm64, it is legal and cheap to issue unaligned 8-byte or - // 16-byte loads and stores. This technique probably wouldn't be as - // effective on architectures that are fussier about alignment. - LDP 0(R6), (R14, R15) - STP (R14, R15), 0(R7) - - // d += length - // s += length - ADD R4, R7, R7 - ADD R4, R6, R6 - B loop - -callMemmove: - // if length > len(dst)-d || length > len(src)-s { etc } - CMP R2, R4 - BGT errCorrupt - CMP R3, R4 - BGT errCorrupt - - // copy(dst[d:], src[s:s+length]) - // - // This means calling runtime·memmove(&dst[d], &src[s], length), so we push - // R7, R6 and R4 as arguments. Coincidentally, we also need to spill those - // three registers to the stack, to save local variables across the CALL. - MOVD R7, 8(RSP) - MOVD R6, 16(RSP) - MOVD R4, 24(RSP) - MOVD R7, 32(RSP) - MOVD R6, 40(RSP) - MOVD R4, 48(RSP) - CALL runtime·memmove(SB) - - // Restore local variables: unspill registers from the stack and - // re-calculate R8-R13. - MOVD 32(RSP), R7 - MOVD 40(RSP), R6 - MOVD 48(RSP), R4 - MOVD dst_base+0(FP), R8 - MOVD dst_len+8(FP), R9 - MOVD R8, R10 - ADD R9, R10, R10 - MOVD src_base+24(FP), R11 - MOVD src_len+32(FP), R12 - MOVD R11, R13 - ADD R12, R13, R13 - - // d += length - // s += length - ADD R4, R7, R7 - ADD R4, R6, R6 - B loop - -tagLit60Plus: - // !!! This fragment does the - // - // s += x - 58; if uint(s) > uint(len(src)) { etc } - // - // checks. In the asm version, we code it once instead of once per switch case. - ADD R4, R6, R6 - SUB $58, R6, R6 - MOVD R6, R3 - SUB R11, R3, R3 - CMP R12, R3 - BGT errCorrupt - - // case x == 60: - MOVW $61, R1 - CMPW R1, R4 - BEQ tagLit61 - BGT tagLit62Plus - - // x = uint32(src[s-1]) - MOVBU -1(R6), R4 - B doLit - -tagLit61: - // case x == 61: - // x = uint32(src[s-2]) | uint32(src[s-1])<<8 - MOVHU -2(R6), R4 - B doLit - -tagLit62Plus: - CMPW $62, R4 - BHI tagLit63 - - // case x == 62: - // x = uint32(src[s-3]) | uint32(src[s-2])<<8 | uint32(src[s-1])<<16 - MOVHU -3(R6), R4 - MOVBU -1(R6), R3 - ORR R3<<16, R4 - B doLit - -tagLit63: - // case x == 63: - // x = uint32(src[s-4]) | uint32(src[s-3])<<8 | uint32(src[s-2])<<16 | uint32(src[s-1])<<24 - MOVWU -4(R6), R4 - B doLit - - // The code above handles literal tags. - // ---------------------------------------- - // The code below handles copy tags. - -tagCopy4: - // case tagCopy4: - // s += 5 - ADD $5, R6, R6 - - // if uint(s) > uint(len(src)) { etc } - MOVD R6, R3 - SUB R11, R3, R3 - CMP R12, R3 - BGT errCorrupt - - // length = 1 + int(src[s-5])>>2 - MOVD $1, R1 - ADD R4>>2, R1, R4 - - // offset = int(uint32(src[s-4]) | uint32(src[s-3])<<8 | uint32(src[s-2])<<16 | uint32(src[s-1])<<24) - MOVWU -4(R6), R5 - B doCopy - -tagCopy2: - // case tagCopy2: - // s += 3 - ADD $3, R6, R6 - - // if uint(s) > uint(len(src)) { etc } - MOVD R6, R3 - SUB R11, R3, R3 - CMP R12, R3 - BGT errCorrupt - - // length = 1 + int(src[s-3])>>2 - MOVD $1, R1 - ADD R4>>2, R1, R4 - - // offset = int(uint32(src[s-2]) | uint32(src[s-1])<<8) - MOVHU -2(R6), R5 - B doCopy - -tagCopy: - // We have a copy tag. We assume that: - // - R3 == src[s] & 0x03 - // - R4 == src[s] - CMP $2, R3 - BEQ tagCopy2 - BGT tagCopy4 - - // case tagCopy1: - // s += 2 - ADD $2, R6, R6 - - // if uint(s) > uint(len(src)) { etc } - MOVD R6, R3 - SUB R11, R3, R3 - CMP R12, R3 - BGT errCorrupt - - // offset = int(uint32(src[s-2])&0xe0<<3 | uint32(src[s-1])) - MOVD R4, R5 - AND $0xe0, R5 - MOVBU -1(R6), R3 - ORR R5<<3, R3, R5 - - // length = 4 + int(src[s-2])>>2&0x7 - MOVD $7, R1 - AND R4>>2, R1, R4 - ADD $4, R4, R4 - -doCopy: - // This is the end of the outer "switch", when we have a copy tag. - // - // We assume that: - // - R4 == length && R4 > 0 - // - R5 == offset - - // if offset <= 0 { etc } - MOVD $0, R1 - CMP R1, R5 - BLE errCorrupt - - // if d < offset { etc } - MOVD R7, R3 - SUB R8, R3, R3 - CMP R5, R3 - BLT errCorrupt - - // if length > len(dst)-d { etc } - MOVD R10, R3 - SUB R7, R3, R3 - CMP R3, R4 - BGT errCorrupt - - // forwardCopy(dst[d:d+length], dst[d-offset:]); d += length - // - // Set: - // - R14 = len(dst)-d - // - R15 = &dst[d-offset] - MOVD R10, R14 - SUB R7, R14, R14 - MOVD R7, R15 - SUB R5, R15, R15 - - // !!! Try a faster technique for short (16 or fewer bytes) forward copies. - // - // First, try using two 8-byte load/stores, similar to the doLit technique - // above. Even if dst[d:d+length] and dst[d-offset:] can overlap, this is - // still OK if offset >= 8. Note that this has to be two 8-byte load/stores - // and not one 16-byte load/store, and the first store has to be before the - // second load, due to the overlap if offset is in the range [8, 16). - // - // if length > 16 || offset < 8 || len(dst)-d < 16 { - // goto slowForwardCopy - // } - // copy 16 bytes - // d += length - CMP $16, R4 - BGT slowForwardCopy - CMP $8, R5 - BLT slowForwardCopy - CMP $16, R14 - BLT slowForwardCopy - MOVD 0(R15), R2 - MOVD R2, 0(R7) - MOVD 8(R15), R3 - MOVD R3, 8(R7) - ADD R4, R7, R7 - B loop - -slowForwardCopy: - // !!! If the forward copy is longer than 16 bytes, or if offset < 8, we - // can still try 8-byte load stores, provided we can overrun up to 10 extra - // bytes. As above, the overrun will be fixed up by subsequent iterations - // of the outermost loop. - // - // The C++ snappy code calls this technique IncrementalCopyFastPath. Its - // commentary says: - // - // ---- - // - // The main part of this loop is a simple copy of eight bytes at a time - // until we've copied (at least) the requested amount of bytes. However, - // if d and d-offset are less than eight bytes apart (indicating a - // repeating pattern of length < 8), we first need to expand the pattern in - // order to get the correct results. For instance, if the buffer looks like - // this, with the eight-byte <d-offset> and <d> patterns marked as - // intervals: - // - // abxxxxxxxxxxxx - // [------] d-offset - // [------] d - // - // a single eight-byte copy from <d-offset> to <d> will repeat the pattern - // once, after which we can move <d> two bytes without moving <d-offset>: - // - // ababxxxxxxxxxx - // [------] d-offset - // [------] d - // - // and repeat the exercise until the two no longer overlap. - // - // This allows us to do very well in the special case of one single byte - // repeated many times, without taking a big hit for more general cases. - // - // The worst case of extra writing past the end of the match occurs when - // offset == 1 and length == 1; the last copy will read from byte positions - // [0..7] and write to [4..11], whereas it was only supposed to write to - // position 1. Thus, ten excess bytes. - // - // ---- - // - // That "10 byte overrun" worst case is confirmed by Go's - // TestSlowForwardCopyOverrun, which also tests the fixUpSlowForwardCopy - // and finishSlowForwardCopy algorithm. - // - // if length > len(dst)-d-10 { - // goto verySlowForwardCopy - // } - SUB $10, R14, R14 - CMP R14, R4 - BGT verySlowForwardCopy - -makeOffsetAtLeast8: - // !!! As above, expand the pattern so that offset >= 8 and we can use - // 8-byte load/stores. - // - // for offset < 8 { - // copy 8 bytes from dst[d-offset:] to dst[d:] - // length -= offset - // d += offset - // offset += offset - // // The two previous lines together means that d-offset, and therefore - // // R15, is unchanged. - // } - CMP $8, R5 - BGE fixUpSlowForwardCopy - MOVD (R15), R3 - MOVD R3, (R7) - SUB R5, R4, R4 - ADD R5, R7, R7 - ADD R5, R5, R5 - B makeOffsetAtLeast8 - -fixUpSlowForwardCopy: - // !!! Add length (which might be negative now) to d (implied by R7 being - // &dst[d]) so that d ends up at the right place when we jump back to the - // top of the loop. Before we do that, though, we save R7 to R2 so that, if - // length is positive, copying the remaining length bytes will write to the - // right place. - MOVD R7, R2 - ADD R4, R7, R7 - -finishSlowForwardCopy: - // !!! Repeat 8-byte load/stores until length <= 0. Ending with a negative - // length means that we overrun, but as above, that will be fixed up by - // subsequent iterations of the outermost loop. - MOVD $0, R1 - CMP R1, R4 - BLE loop - MOVD (R15), R3 - MOVD R3, (R2) - ADD $8, R15, R15 - ADD $8, R2, R2 - SUB $8, R4, R4 - B finishSlowForwardCopy - -verySlowForwardCopy: - // verySlowForwardCopy is a simple implementation of forward copy. In C - // parlance, this is a do/while loop instead of a while loop, since we know - // that length > 0. In Go syntax: - // - // for { - // dst[d] = dst[d - offset] - // d++ - // length-- - // if length == 0 { - // break - // } - // } - MOVB (R15), R3 - MOVB R3, (R7) - ADD $1, R15, R15 - ADD $1, R7, R7 - SUB $1, R4, R4 - CBNZ R4, verySlowForwardCopy - B loop - - // The code above handles copy tags. - // ---------------------------------------- - -end: - // This is the end of the "for s < len(src)". - // - // if d != len(dst) { etc } - CMP R10, R7 - BNE errCorrupt - - // return 0 - MOVD $0, ret+48(FP) - RET - -errCorrupt: - // return decodeErrCodeCorrupt - MOVD $1, R2 - MOVD R2, ret+48(FP) - RET |