Line data    Source code

       1             : // Copyright 2024 The LevelDB-Go and Pebble Authors. All rights reserved. Use
       2             : // of this source code is governed by a BSD-style license that can be found in
       3             : // the LICENSE file.
       4             : 
       5             : package colblk
       6             : 
       7             : import "golang.org/x/exp/constraints"
       8             : 
       9             : // align returns the next value greater than or equal to offset that's divisible
      10             : // by val.
      11           1 : func align[T constraints.Integer](offset, val T) T {
      12           1 :         return (offset + val - 1) & ^(val - 1)
      13           1 : }
      14             : 
      15             : // alignWithZeroes aligns the provided offset to val, and writing zeroes to any
      16             : // bytes in buf between the old offset and new aligned offset. This provides
      17             : // determinism when reusing memory that has not been zeroed.
      18           1 : func alignWithZeroes[T constraints.Integer](buf []byte, offset, val T) T {
      19           1 :         aligned := align[T](offset, val)
      20           1 :         for i := offset; i < aligned; i++ {
      21           0 :                 buf[i] = 0
      22           0 :         }
      23           1 :         return aligned
      24             : }
      25             : 
      26             : const (
      27             :         align16 = 2
      28             :         align32 = 4
      29             :         align64 = 8
      30             : )
      31             : 
      32             : // When multiplying or dividing by align{16,32,64} using signed integers, it's
      33             : // faster to shift to the left to multiply or shift to the right to divide. (The
      34             : // compiler optimization is limited to unsigned integers.) The below constants
      35             : // define the shift amounts corresponding to the above align constants.  (eg,
      36             : // alignNShift = log(alignN)).
      37             : //
      38             : // TODO(jackson): Consider updating usages to use uints? They can be less
      39             : // ergonomic.
      40             : const (
      41             :         align16Shift = 1
      42             :         align32Shift = 2
      43             :         align64Shift = 3
      44             : )