github.com/bhojpur/cache@v0.0.4/pkg/memory/unsafe.go (about)

     1  package memory
     2  
     3  // Copyright (c) 2018 Bhojpur Consulting Private Limited, India. All rights reserved.
     4  
     5  // Permission is hereby granted, free of charge, to any person obtaining a copy
     6  // of this software and associated documentation files (the "Software"), to deal
     7  // in the Software without restriction, including without limitation the rights
     8  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
     9  // copies of the Software, and to permit persons to whom the Software is
    10  // furnished to do so, subject to the following conditions:
    11  
    12  // The above copyright notice and this permission notice shall be included in
    13  // all copies or substantial portions of the Software.
    14  
    15  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    16  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    17  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    18  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    19  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    20  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    21  // THE SOFTWARE.
    22  
    23  import (
    24  	"reflect"
    25  	"unsafe"
    26  )
    27  
    28  func unsafeAdd(base unsafe.Pointer, offset uintptr) unsafe.Pointer {
    29  	return unsafe.Pointer(uintptr(base) + offset)
    30  }
    31  
    32  func unsafeIndex(base unsafe.Pointer, offset uintptr, elemsz uintptr, n int) unsafe.Pointer {
    33  	return unsafe.Pointer(uintptr(base) + offset + uintptr(n)*elemsz)
    34  }
    35  
    36  func unsafeByteSlice(base unsafe.Pointer, offset uintptr, i, j int) []byte {
    37  	// This memory is not allocated from C, but it is unmanaged by Go's
    38  	// garbage collector and should behave similarly, and the compiler
    39  	// should produce similar code.  Note that this conversion allows a
    40  	// subslice to begin after the base address, with an optional offset,
    41  	// while the URL above does not cover this case and only slices from
    42  	// index 0.  However, the wiki never says that the address must be to
    43  	// the beginning of a C allocation (or even that malloc was used at
    44  	// all), so this is believed to be correct.
    45  	return (*[maxAllocSize]byte)(unsafeAdd(base, offset))[i:j:j]
    46  }
    47  
    48  // unsafeSlice modifies the data, len, and cap of a slice variable pointed to by
    49  // the slice parameter.  This helper should be used over other direct
    50  // manipulation of reflect.SliceHeader to prevent misuse, namely, converting
    51  // from reflect.SliceHeader to a Go slice type.
    52  func unsafeSlice(slice, data unsafe.Pointer, len int) {
    53  	s := (*reflect.SliceHeader)(slice)
    54  	s.Data = uintptr(data)
    55  	s.Cap = len
    56  	s.Len = len
    57  }