github.com/mh-cbon/go@v0.0.0-20160603070303-9e112a3fe4c0/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  //go:noescape
    19  func castagnoliSSE42(crc uint32, p []byte) uint32
    20  
    21  // ieeeCLMUL is defined in crc_amd64.s and uses the PCLMULQDQ
    22  // instruction as well as SSE 4.1.
    23  //go:noescape
    24  func ieeeCLMUL(crc uint32, p []byte) uint32
    25  
    26  var sse42 = haveSSE42()
    27  var useFastIEEE = haveCLMUL() && haveSSE41()
    28  
    29  func updateCastagnoli(crc uint32, p []byte) uint32 {
    30  	if sse42 {
    31  		return castagnoliSSE42(crc, p)
    32  	}
    33  	// Use slicing-by-8 on larger inputs.
    34  	if len(p) >= sliceBy8Cutoff {
    35  		return updateSlicingBy8(crc, castagnoliTable8, p)
    36  	}
    37  	return update(crc, castagnoliTable, p)
    38  }
    39  
    40  func updateIEEE(crc uint32, p []byte) uint32 {
    41  	if useFastIEEE && len(p) >= 64 {
    42  		left := len(p) & 15
    43  		do := len(p) - left
    44  		crc = ^ieeeCLMUL(^crc, p[:do])
    45  		if left > 0 {
    46  			crc = update(crc, IEEETable, p[do:])
    47  		}
    48  		return crc
    49  	}
    50  
    51  	// Use slicing-by-8 on larger inputs.
    52  	if len(p) >= sliceBy8Cutoff {
    53  		ieeeTable8Once.Do(func() {
    54  			ieeeTable8 = makeTable8(IEEE)
    55  		})
    56  		return updateSlicingBy8(crc, ieeeTable8, p)
    57  	}
    58  
    59  	return update(crc, IEEETable, p)
    60  }