github.com/grailbio/base@v0.0.11/simd/multibyte_appengine.go (about)

     1  // Copyright 2018 GRAIL, Inc.  All rights reserved.
     2  // Use of this source code is governed by the Apache-2.0
     3  // license that can be found in the LICENSE file.
     4  
     5  // +build appengine
     6  
     7  package simd
     8  
     9  // This file contains functions which operate on slices of 2- or 4-byte
    10  // elements (typically small structs or integers) in ways that differ from the
    11  // corresponding operations on single-byte elements.
    12  // In this context, there is little point in making the interface based on
    13  // []byte, since the caller will need to unsafely cast to it.  Instead, most
    14  // functions take unsafe.Pointer(s) and a count, and have names ending in
    15  // 'Raw'; the caller should write safe wrappers around them when appropriate.
    16  // We provide sample wrappers for the int16 and uint16 cases.  (Originally did
    17  // this for int32/uint32, but turns out the compiler has hardcoded
    18  // optimizations for those cases which are currently missing for {u}int16.)
    19  
    20  // RepeatI16 fills dst[] with the given int16.
    21  func RepeatI16(dst []int16, val int16) {
    22  	for i := range dst {
    23  		dst[i] = val
    24  	}
    25  }
    26  
    27  // RepeatU16 fills dst[] with the given uint16.
    28  func RepeatU16(dst []uint16, val uint16) {
    29  	for i := range dst {
    30  		dst[i] = val
    31  	}
    32  }
    33  
    34  // ReverseI16Inplace reverses a []int16 in-place.
    35  func ReverseI16Inplace(main []int16) {
    36  	nElem := len(main)
    37  	nElemDiv2 := nElem >> 1
    38  	for i, j := 0, nElem-1; i != nElemDiv2; i, j = i+1, j-1 {
    39  		main[i], main[j] = main[j], main[i]
    40  	}
    41  }
    42  
    43  // ReverseU16Inplace reverses a []uint16 in-place.
    44  func ReverseU16Inplace(main []uint16) {
    45  	nElem := len(main)
    46  	nElemDiv2 := nElem >> 1
    47  	for i, j := 0, nElem-1; i != nElemDiv2; i, j = i+1, j-1 {
    48  		main[i], main[j] = main[j], main[i]
    49  	}
    50  }
    51  
    52  // ReverseI16 sets dst[len(src) - 1 - pos] := src[pos] for each position in
    53  // src.  It panics if len(src) != len(dst).
    54  func ReverseI16(dst, src []int16) {
    55  	if len(dst) != len(src) {
    56  		panic("ReverseI16() requires len(src) == len(dst).")
    57  	}
    58  	nElemMinus1 := len(dst) - 1
    59  	for i := range dst {
    60  		dst[i] = src[nElemMinus1-i]
    61  	}
    62  }
    63  
    64  // ReverseU16 sets dst[len(src) - 1 - pos] := src[pos] for each position in
    65  // src.  It panics if len(src) != len(dst).
    66  func ReverseU16(dst, src []uint16) {
    67  	if len(dst) != len(src) {
    68  		panic("ReverseU16() requires len(src) == len(dst).")
    69  	}
    70  	nElemMinus1 := len(dst) - 1
    71  	for i := range dst {
    72  		dst[i] = src[nElemMinus1-i]
    73  	}
    74  }
    75  
    76  // Benchmark results suggest that Reverse32Raw is unimportant.