github.com/q45/go@v0.0.0-20151101211701-a4fb8c13db3f/src/hash/crc32/crc32_amd64.go (about)

     1  // Copyright 2011 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package crc32
     6  
     7  // This file contains the code to call the SSE 4.2 version of the Castagnoli
     8  // and IEEE CRC.
     9  
    10  // haveSSE41/haveSSE42/haveCLMUL are defined in crc_amd64.s and use
    11  // CPUID to test for SSE 4.1, 4.2 and CLMUL support.
    12  func haveSSE41() bool
    13  func haveSSE42() bool
    14  func haveCLMUL() bool
    15  
    16  // castagnoliSSE42 is defined in crc_amd64.s and uses the SSE4.2 CRC32
    17  // instruction.
    18  func castagnoliSSE42(crc uint32, p []byte) uint32
    19  
    20  // ieeeCLMUL is defined in crc_amd64.s and uses the PCLMULQDQ
    21  // instruction as well as SSE 4.1.
    22  func ieeeCLMUL(crc uint32, p []byte) uint32
    23  
    24  var sse42 = haveSSE42()
    25  var useFastIEEE = haveCLMUL() && haveSSE41()
    26  
    27  func updateCastagnoli(crc uint32, p []byte) uint32 {
    28  	if sse42 {
    29  		return castagnoliSSE42(crc, p)
    30  	}
    31  	return update(crc, castagnoliTable, p)
    32  }
    33  
    34  func updateIEEE(crc uint32, p []byte) uint32 {
    35  	if useFastIEEE && len(p) >= 64 {
    36  		left := len(p) & 15
    37  		do := len(p) - left
    38  		crc = ^ieeeCLMUL(^crc, p[:do])
    39  		if left > 0 {
    40  			crc = update(crc, IEEETable, p[do:])
    41  		}
    42  		return crc
    43  	}
    44  
    45  	// only use slicing-by-8 when input is >= 4KB
    46  	if len(p) >= 4096 {
    47  		iEEETable8Once.Do(func() {
    48  			iEEETable8 = makeTable8(IEEE)
    49  		})
    50  		return updateSlicingBy8(crc, iEEETable8, p)
    51  	}
    52  
    53  	return update(crc, IEEETable, p)
    54  }