github.com/sean-/go@v0.0.0-20151219100004-97f854cd7bb6/src/hash/crc32/crc32_amd64p32.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  // CRC.
     9  
    10  // haveSSE42 is defined in crc_amd64p32.s and uses CPUID to test for SSE 4.2
    11  // support.
    12  func haveSSE42() bool
    13  
    14  // castagnoliSSE42 is defined in crc_amd64.s and uses the SSE4.2 CRC32
    15  // instruction.
    16  //go:noescape
    17  func castagnoliSSE42(crc uint32, p []byte) uint32
    18  
    19  var sse42 = haveSSE42()
    20  
    21  func updateCastagnoli(crc uint32, p []byte) uint32 {
    22  	if sse42 {
    23  		return castagnoliSSE42(crc, p)
    24  	}
    25  	return update(crc, castagnoliTable, p)
    26  }
    27  
    28  func updateIEEE(crc uint32, p []byte) uint32 {
    29  	// only use slicing-by-8 when input is >= 4KB
    30  	if len(p) >= 4096 {
    31  		ieeeTable8Once.Do(func() {
    32  			ieeeTable8 = makeTable8(IEEE)
    33  		})
    34  		return updateSlicingBy8(crc, ieeeTable8, p)
    35  	}
    36  
    37  	return update(crc, IEEETable, p)
    38  }