lab.nexedi.com/kirr/go123@v0.0.0-20240207185015-8299741fa871/xbytes/alloc.go (about)

     1  // Copyright (C) 2017-2018  Nexedi SA and Contributors.
     2  //                          Kirill Smelkov <kirr@nexedi.com>
     3  //
     4  // This program is free software: you can Use, Study, Modify and Redistribute
     5  // it under the terms of the GNU General Public License version 3, or (at your
     6  // option) any later version, as published by the Free Software Foundation.
     7  //
     8  // You can also Link and Combine this program with other software covered by
     9  // the terms of any of the Free Software licenses or any of the Open Source
    10  // Initiative approved licenses and Convey the resulting work. Corresponding
    11  // source of such a combination shall include the source code for all other
    12  // software used.
    13  //
    14  // This program is distributed WITHOUT ANY WARRANTY; without even the implied
    15  // warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
    16  //
    17  // See COPYING file for full licensing terms.
    18  // See https://www.nexedi.com/licensing for rationale and options.
    19  
    20  // (re)allocation routines for []byte.
    21  
    22  package xbytes
    23  
    24  import (
    25  	"lab.nexedi.com/kirr/go123/xmath"
    26  )
    27  
    28  // Grow increases length of byte slice by n elements.
    29  //
    30  // If there is not enough capacity the slice is reallocated and copied.
    31  // The memory for grown elements is not initialized.
    32  func Grow(b []byte, n int) []byte {
    33  	ln := len(b) + n
    34  	if ln <= cap(b) {
    35  		return b[:ln]
    36  	}
    37  
    38  	bb := make([]byte, ln, xmath.CeilPow2(uint64(ln)))
    39  	copy(bb, b)
    40  	return bb
    41  }
    42  
    43  // MakeRoom makes sure cap(b) - len(b) >= n.
    44  //
    45  // If there is not enough capacity the slice is reallocated and copied.
    46  // Length of the slice remains unchanged.
    47  func MakeRoom(b []byte, n int) []byte {
    48  	ln := len(b) + n
    49  	if ln <= cap(b) {
    50  		return b
    51  	}
    52  
    53  	bb := make([]byte, len(b), xmath.CeilPow2(uint64(ln)))
    54  	copy(bb, b)
    55  	return bb
    56  }
    57  
    58  // Resize resizes byte slice to be of length n.
    59  //
    60  // If slice length is increased and there is not enough capacity, the slice is reallocated and copied.
    61  // The memory for grown elements, if any, is not initialized.
    62  func Resize(b []byte, n int) []byte {
    63  	if cap(b) >= n {
    64  		return b[:n]
    65  	}
    66  
    67  	bb := make([]byte, n, xmath.CeilPow2(uint64(n)))
    68  	copy(bb, b)
    69  	return bb
    70  }
    71  
    72  
    73  // Realloc resizes byte slice to be of length n not preserving content.
    74  //
    75  // If slice length is increased and there is not enough capacity, the slice is reallocated but not copied.
    76  // The memory for all elements becomes uninitialized.
    77  //
    78  // NOTE semantic is different from C realloc(3) where content is preserved.
    79  // NOTE use Resize when you need to preserve slice content.
    80  func Realloc(b []byte, n int) []byte {
    81  	return Realloc64(b, int64(n))
    82  }
    83  
    84  // Realloc64 is the same as Realloc but for size typed as int64.
    85  func Realloc64(b []byte, n int64) []byte {
    86  	if int64(cap(b)) >= n {
    87  		return b[:n]
    88  	}
    89  
    90  	return make([]byte, n, xmath.CeilPow2(uint64(n)))
    91  }