// Copyright 2011 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.

#define NOSPLIT 4
#define RODATA 8

// func castagnoliSSE42(crc uint32, p []byte) uint32
TEXT ·castagnoliSSE42(SB), NOSPLIT, $0
	MOVL crc+0(FP), AX    // CRC value
	MOVQ p+8(FP), SI      // data pointer
	MOVQ p_len+16(FP), CX // len(p)

	NOTL AX

	// If there's less than 8 bytes to process, we do it byte-by-byte.
	CMPQ CX, $8
	JL   cleanup

	// Process individual bytes until the input is 8-byte aligned.
startup:
	MOVQ SI, BX
	ANDQ $7, BX
	JZ   aligned

	CRC32B (SI), AX
	DECQ   CX
	INCQ   SI
	JMP    startup

aligned:
	// The input is now 8-byte aligned and we can process 8-byte chunks.
	CMPQ CX, $8
	JL   cleanup

	CRC32Q (SI), AX
	ADDQ   $8, SI
	SUBQ   $8, CX
	JMP    aligned

cleanup:
	// We may have some bytes left over that we process one at a time.
	CMPQ CX, $0
	JE   done

	CRC32B (SI), AX
	INCQ   SI
	DECQ   CX
	JMP    cleanup

done:
	NOTL AX
	MOVL AX, ret+32(FP)
	RET

// func haveSSE42() bool
TEXT ·haveSSE42(SB), NOSPLIT, $0
	XORQ AX, AX
	INCL AX
	CPUID
	SHRQ $20, CX
	ANDQ $1, CX
	MOVB CX, ret+0(FP)
	RET

// func haveCLMUL() bool
TEXT ·haveCLMUL(SB), NOSPLIT, $0
	XORQ AX, AX
	INCL AX
	CPUID
	SHRQ $1, CX
	ANDQ $1, CX
	MOVB CX, ret+0(FP)
	RET

// func haveSSE41() bool
TEXT ·haveSSE41(SB), NOSPLIT, $0
	XORQ AX, AX
	INCL AX
	CPUID
	SHRQ $19, CX
	ANDQ $1, CX
	MOVB CX, ret+0(FP)
	RET

// CRC32 polynomial data
//
// These constants are lifted from the
// Linux kernel, since they avoid the costly
// PSHUFB 16 byte reversal proposed in the
// original Intel paper.
DATA r2r1<>+0(SB)/8, $0x154442bd4
DATA r2r1<>+8(SB)/8, $0x1c6e41596
DATA r4r3<>+0(SB)/8, $0x1751997d0
DATA r4r3<>+8(SB)/8, $0x0ccaa009e
DATA rupoly<>+0(SB)/8, $0x1db710641
DATA rupoly<>+8(SB)/8, $0x1f7011641
DATA r5<>+0(SB)/8, $0x163cd6124

GLOBL r2r1<>(SB), RODATA, $16
GLOBL r4r3<>(SB), RODATA, $16
GLOBL rupoly<>(SB), RODATA, $16
GLOBL r5<>(SB), RODATA, $8

// Based on http://www.intel.com/content/dam/www/public/us/en/documents/white-papers/fast-crc-computation-generic-polynomials-pclmulqdq-paper.pdf
// len(p) must be at least 64, and must be a multiple of 16.

// func ieeeCLMUL(crc uint32, p []byte) uint32
TEXT ·ieeeCLMUL(SB), NOSPLIT, $0
	MOVL crc+0(FP), X0    // Initial CRC value
	MOVQ p+8(FP), SI      // data pointer
	MOVQ p_len+16(FP), CX // len(p)

	MOVOU (SI), X1
	MOVOU 16(SI), X2
	MOVOU 32(SI), X3
	MOVOU 48(SI), X4
	PXOR  X0, X1
	ADDQ  $64, SI    // buf+=64
	SUBQ  $64, CX    // len-=64
	CMPQ  CX, $64    // Less than 64 bytes left
	JB    remain64

	MOVOU r2r1<>+0(SB), X0

loopback64:
	MOVOA X1, X5
	MOVOA X2, X6
	MOVOA X3, X7
	MOVOA X4, X8

	PCLMULQDQ $0, X0, X1
	PCLMULQDQ $0, X0, X2
	PCLMULQDQ $0, X0, X3
	PCLMULQDQ $0, X0, X4

	// Load next early
	MOVOU (SI), X11
	MOVOU 16(SI), X12
	MOVOU 32(SI), X13
	MOVOU 48(SI), X14

	PCLMULQDQ $0x11, X0, X5
	PCLMULQDQ $0x11, X0, X6
	PCLMULQDQ $0x11, X0, X7
	PCLMULQDQ $0x11, X0, X8

	PXOR X5, X1
	PXOR X6, X2
	PXOR X7, X3
	PXOR X8, X4

	PXOR X11, X1
	PXOR X12, X2
	PXOR X13, X3
	PXOR X14, X4

	ADDQ $0x40, DI
	ADDQ $64, SI    // buf+=64
	SUBQ $64, CX    // len-=64
	CMPQ CX, $64    // Less than 64 bytes left?
	JGE  loopback64

	// Fold result into a single register (X1)
remain64:
	MOVOU r4r3<>+0(SB), X0

	MOVOA     X1, X5
	PCLMULQDQ $0, X0, X1
	PCLMULQDQ $0x11, X0, X5
	PXOR      X5, X1
	PXOR      X2, X1

	MOVOA     X1, X5
	PCLMULQDQ $0, X0, X1
	PCLMULQDQ $0x11, X0, X5
	PXOR      X5, X1
	PXOR      X3, X1

	MOVOA     X1, X5
	PCLMULQDQ $0, X0, X1
	PCLMULQDQ $0x11, X0, X5
	PXOR      X5, X1
	PXOR      X4, X1

	// More than 16 bytes left?
	CMPQ CX, $16
	JB   finish

	// Encode 16 bytes
remain16:
	MOVOU     (SI), X10
	MOVOA     X1, X5
	PCLMULQDQ $0, X0, X1
	PCLMULQDQ $0x11, X0, X5
	PXOR      X5, X1
	PXOR      X10, X1
	SUBQ      $16, CX
	ADDQ      $16, SI
	CMPQ      CX, $16
	JGE       remain16

finish:
	// Fold final result into 32 bits and return it
	PCMPEQB   X3, X3
	PCLMULQDQ $1, X1, X0
	PSRLDQ    $8, X1
	PXOR      X0, X1

	MOVOA X1, X2
	MOVQ  r5<>+0(SB), X0

	// Creates 32 bit mask. Note that we don't care about upper half.
	PSRLQ $32, X3

	PSRLDQ    $4, X2
	PAND      X3, X1
	PCLMULQDQ $0, X0, X1
	PXOR      X2, X1

	MOVOU rupoly<>+0(SB), X0

	MOVOA     X1, X2
	PAND      X3, X1
	PCLMULQDQ $0x10, X0, X1
	PAND      X3, X1
	PCLMULQDQ $0, X0, X1
	PXOR      X2, X1

	// PEXTRD   $1, X1, AX  (SSE 4.1)
	BYTE $0x66; BYTE $0x0f; BYTE $0x3a
	BYTE $0x16; BYTE $0xc8; BYTE $0x01
	MOVL AX, ret+32(FP)

	RET
